Our Captive Cousins: The Plight of Great Apes in Zoos

Published: July 2025

11 The Landscape of Captive Great Apes in European Zoos Gorillas

Case Study: Massa Chimpanzees Case Study: Santino

28 Captivity Related Injury, Illness, and Death of Great Apes

Diet and Obesity

Disease and Illness

Cardiovascular Disease

Infectious Diseases and Zoonoses

Conflict

Case Study: Austin and Bossou

Escapes

Case Study: Linda, Santino, Manda, Torsten, and Selma

Case Study: Bazoo

Case Study: Mike and Karibuna

33 Human Health and Safety

Case Study: Harambe Case Study: Malabo Case Study: Bako Case Study: Bokito

36 Primate Conservation and the Role (or otherwise) of Zoos

The Impact of Breeding Great Apes in Zoos on Conservation

Hybridisation of Apes in Zoos 38 Legislation EU Zoos Directive Zoo Licensing Act 1981 Standards of Modern Zoo Practice for Great Britain

40 Conclusion

42 References

F O R E WO R D :

G R E AT A P E S D O N ’ T B E L O N G I N ZO O S

Jimmy & Jenny Desmond, Liberia Chimpanzee Rescue & Protection

Keeping great apes in zoos is no longer et hically defensible. Zoos simply cannot meet t he psychological, physical, and social needs of cognitively and socially complex beings. Despite claiming conser vation and education benefits, zoos perpetuate harmful messaging, promote unnecessar y breeding and treat individuals as commodities.

Zoos often market great apes as conservation ‘ambassadors’, but the reality is that seeing great apes behind glass undermines public perception of their endangered status. People viewing great apes in zoos may believe the species are safe and plentiful, while wild populations are, in fact, rapidly declining. In a zoo setting, visitors can forget that these individuals deserve dignity and respect.

Captive-bred apes do not make good candidates for release into the wild - they are bred for display, not conservation Claims that coordinated zoo breeding programmes in Europe and Nor th America are key to the conservation of these species in the wild simply don’t withstand scrutiny Zoo-bred great apes may not have the behavioural skills or the appropriate genetic make-up to enable them to be integrated into existing wild populations, and may introduce or become victims of diseases The overwhelming majority of great apes in zoos will never be reintroduced to the wild

There are real consequences that result from the keeping and breeding of great apes in such ar tificial captive environments, including high rates of stillbir ths, maternal rejection, instances of infanticide, and infants who must be human-reared Imagine being a mother, living in a cage while pregnant, being stared at, subjected to testing and medical interventions you shouldn’t need at all, then giving bir th to a baby you don’t know how to care for and who may very well be taken from you. Imagine being an infant intentionally created by humans for enter tainment and observation, being rejected by your mother, passed around to multiple carers and frequently left alone. The breeding of great apes in zoos does not justify the decades of unnatural captivity that face newborn individuals, should they survive.

Life in captivity harms the health and wellbeing of great apes Captive chimpanzees suffer from hear t disease, obesity, and social dysfunction They lack the space and complexity of natural environments, and the frequent transfer of individuals between zoos, often driven by funding or logistics, disrupts the fragile social bonds within captive groups Apes in zoos are stripped of culture, autonomy, and dignity, and zoos cannot mimic or maintain great ape culture, knowledge, or generational learning Even in the best facilities, they are often moved or bred based on industry needs

By contrast, sanctuaries offer a more ethical and effective alternative True sanctuaries exist only out of necessity Sanctuaries avoid breeding and some - par ticularly those located in native ranges - offer access to forests and more natural social dynamics Genuine sanctuaries provide lifelong care for individuals rescued from labs, enter tainment, or private ownership and, frequently, profound physical and emotional transformations are witnessed when individuals are allowed to live in environments that better reflect their natural world. If reintroductions into the wild are to be under taken, apes in sanctuaries make far better candidates than zoo apes, especially those already living in native ranges and forest environments and holding local culture and knowledge

A practical and immediate step forward is to end the breeding of great apes in zoos, allowing for a gradual, responsible phase out of great ape captivity Zoos can continue to fund conservation, educate the public, and evolve their missions, without holding apes in ar tificial, restrictive conditions Zoos can be presented with a roadmap toward ethical reform In only one generation, great apes could be phased out of zoos, and the few remaining individuals transferred to appropriate genuine sanctuaries

Great apes do not belong in zoos It is time to reimagine how we perceive and interact with our closest cousins and put a stop to exploitation, deprivation, and suffering The way forward embraces respect for their intelligence, their emotional depth, and their right to a life of dignity!

E X E C U T I V E S U M M A RY

W ill Traver s OBE, Co-Founder and Executive President, Born Free Foundation

There isn ’t a single non-human great ape species t hat does not face a bleak and uncer tain future as a direc t result of t he ac tions of t heir closes t living relatives – us!

We destroy their forest homes, hunt them for 'bushmeat', steal their babies for ‘pets’, and confine them to a life in zoos and menageries with little-to-no chance of them ever experiencing their natural homes.

All great apes, including humans, are profoundly social animals who live in complex groups and have a high capacity for learning and passing cultural knowledge down through the generations In zoos, however, these complex structures which frequently express themselves across large social units are almost impossible to replicate in small groups in which individuals have no autonomy, little ability to choose who to associate with, and no option to disperse during times of conflict Who you reproduce with is selected by those who keep you captive Such limited cultural and social oppor tunities and choices could not be fur ther from the range and diversity experienced by their wild kin

Great apes in zoos are also, almost exclusively, kept in environmental and climatic conditions completely alien to those for which they have evolved As a result, in zoos they typically suffer from a range of captivity-related health issues and diseases. Sedentary lifestyles result in obesity; inadequate physical and psychological environments culminate in unnatural behaviours; stressed individuals may be administered antidepressant medication; females, lacking social learning oppor tunities, reject or are unable to care for their young; and breeding programmes ‘overstocked’ with males put the lives of those deemed ‘surplus’ to requirement in jeopardy

This repor t is published within weeks of the publication of new zoo standards for British zoos This is an oppor tunity for zoos to reevaluate their approach to the conservation and protection of great apes, a chance for them to redirect their effor ts to the safeguarding of wild great ape populations and their habitats, and a time for them to acknowledge that neither can they meet the complex societal and behavioural needs of great ape species, nor are their ex situ breeding effor ts truly contributing to securing the future of great ape species in the wild

Our Captive Cousins – The Plight of Great Apes in Zoos, concludes that the keeping of great apes in zoos can no longer be practicably or ethically justified. Great apes should no longer be kept in zoos. The breeding and impor tation of great apes into UK zoos should stop immediately.

In the shor t term, the welfare of great apes in UK zoos should be prioritised through the robust and thorough implementation of the Great Ape Appendix within the recently revised Standards of Modern Zoo Practice for Great Britain However, we should recognise that this is a temporary fix and that the standards fall woefully shor t of what might be regarded by many great ape exper ts as a basic minimum

In the medium term, whilst prioritising the welfare needs of the individual animals concerned, UK zoos and other stakeholders must work together to phase out the keeping of great apes in captivity and redirect their effor ts towards the genuine protection and conservation of wild great apes and their habitats

In the long term, we call on national governments, regulators, national and regional zoo associations and NGOs (non-governmental organisations) to completely recalibrate their approach to great ape conservation, and to work together, humanely, compassionately, and respectfully to phase out the keeping of great apes from zoological collections within Europe, and around the world

P R I M AT E S

The classification of primates has been subject to debate, conflict, and change over centuries – in par ticular as scientists considered evolutionary theory positioning humans as apes. For taxonomic purposes, the order of primates is divided into three distinct suborders, known in common language as Prosimians, New World monkeys, and Old World primates.

Great apes include chimpanzees, gorillas, bonobos, orangutans, and humans They are all par t of the Old World suborder of primates, which also include gibbons (which are usually separately classified as 'lesser apes ' or ‘small apes’), and over 130 species of monkey

All apes, including humans, share cer tain defining characteristics They are profoundly social animals who live in complex social groups and hierarchies They have large brains relative to their body size, making them par ticularly adept at problem-solving They have forward-facing eyes giving binocular vision, and the ability to grasp and manipulate objects, which they may use as tools, using opposable thumbs They have few offspring, long childhoods, and a high capacity for learning, passing cultural knowledge down through the generations They have hair rather than fur and lack tails Many of these characteristics are shared, to a greater or lesser extent, with other primates.

The fact that humans and other apes are closely related provides us with a unique oppor tunity to understand them and empathise with their suffering when they experience harm. It also allows us to predict what practices may cause them harm based on our own human experiences As such, when apes are held captive in zoos, denied the ability to express their wide range of natural behaviours, have their young taken from them for various captive management purposes (for example, to be hand-reared, or transferred to another zoo), or are prevented from choosing their friends and mates (and experience trauma as a result), we can arguably better appreciate their suffering at a personal level than might be the case for other species For these, and other reasons that will be explored in this repor t, we maintain that great apes cannot thrive in a zoo environment, and that the keeping of apes in captivity for public display should be phased out

1. P RO S I M I A N S

This group includes lemurs, tarsiers, lorises, and bushbabies

2. O L D WO R L D M O N K E YS

Those monkeys found across Africa and Asia consisting of bet ween 130 – 140 species, depending on the classification models employed.1

3. N E W WO R L D M O N K E YS

Those monkeys found across the Americas, consisting of around 160 species, depending on the classification models employed.

4. A P E S

Group consisting of chimpanzees, bonobos, gorillas, orangutans, humans, and gibbons

G R E AT A P E S O F A F R I C A

E AS T E R N G O R I L L A

Gorilla beringei

Subspecies: G b beringei (Mountain) and G b graueri (Grauer’s or Eastern Lowland)

Range: Democratic Republic of the Congo; Rwanda; Uganda

Habitat: Lowland to montane rainforest 600-2,900m (Grauer’s) and montane rainforest up to Afro-Alpine zone at 4,000m (Mountain)

Population: 2,600 – 5,000 (Grauer’s); 1,063 (Mountain) (2019)

Lifespan: 35-45 years

Major threats: Poaching for bushmeat and/or capture of infants; persecution for crop-raiding; disease; snares set for other animals; climate change

IUCN* status: Critically Endangered

W E S T E R N G O R I L L A

Gorilla gorilla

Subspecies: G g gorilla (Western Lowland) and G g diehli (Cross River)

Range: Angola; Cameroon; Central African Republic; Congo; Equatorial Guinea; Gabon; Nigeria

Habitat: Primary and secondary tropical rainforest

Population: 95,000 - 316,000 (2018); Cross River

Gorilla fewer than 250

Lifespan: 35-45 years

Major threats: Poaching for bushmeat, traditional medicine, and/or capture of infants; disease, especially Ebola; deforestation and forest fragmentation for logging, mining and plantations; climate change

IUCN status: Critically Endangered

B O N O B O Pan paniscus

Range: Democratic Republic of the Congo

Habitat: Tropical rainforest to forest savannah mosaic in the south of the range

Population: 15-20,000 (2015)

Lifespan: Approx 40 years

Major threats: Poaching for bushmeat, traditional medicine, or capture of live infants; disease; deforestation and forest fragmentation for logging and plantations; climate change

IUCN status: Endangered

C H I M PA N Z E E Pan troglodytes

Subspecies: P t troglodytes (Central); P t verus (Western); P t schweinfur thii (Eastern); P t ellioti (Nigeria-Cameroon)

Range: 21 countries across Africa from southern Senegal and Guinea to western Uganda down to western Tanzania

Habitat: Tropical rainforest, swamp forest, dry forest and gallery forest in savannah-woodland and edges of farmland

Population: 208,500 – 302,000 (2016)

Lifespan: Approx 40 years

Major threats: Poaching for bushmeat, traditional medicine and/or capture of infants; disease, especially Ebola; deforestation and forest fragmentation for logging, mining and plantations; retaliation for crop-raiding; climate change

IUCN status: Endangered

XO N A N D S O F G R E A I N 2

Paul Warneke, flickrcreativecommons

Tim Laman, Wikimediacommons

S

B O R N E A N O R A N G U TA N Pongo pygmaeus

Subspecies: P p pygmaeus (Nor thwest Bornean), P p morio (Nor theast) and P p wurmbii (Central)

Range: Indonesia (Kalimantan); Malaysia (Sabah, Sarawak)

Habitat: Lowland tropical rainforest and peat swamp forest, mostly below 500m

Population: 134,200 (2018)

Lifespan: 45-50 years

Major threats: Deforestation; bushfires; targeted for meat and/or live infants; persecution (often due to crop-raiding); climate change

IUCN status: Critically Endangered

Pongo abelii

Range: Indonesia

Habitat: Lowland rainforest, peatswamp forest and montane rainforest up to 1,500m

Population: 13,900 (2018)

Lifespan: Approx 45 years

Major threats: Deforestation for plantations; habitat fragmentation by roads; dams flooding habitat; illegal killing of adults and capture of infants for sale as pets; climate change

IUCN status: Critically Endangered TA PA N U L I O R A N G U TA N Pongo tapanuliensis

Range: Indonesia, found only in Batang Toru region

Habitat: Lowland rainforest, peat-swamp forest and montane rainforest up to 1,500m

Population: 800 (2017)

Lifespan: Approx 45 years

Major threats: Deforestation for plantations; habitat fragmentation by roads; dams flooding habitat; illegal killing of adults and capture of live infants for sale as pets; climate change

IUCN status: Critically Endangered

Data from Redmond (2018), updated where new figures are available 2 *International Union for the Conservation of Nature

T H E H I S T O RY O F G R E AT A P E S I N ZO O S

Great apes have been held captive in British zoos since at least 1835 Tommy the chimpanzee was the first great ape to live at a British zoo – Regent’s Park Zoo in London (also known as London Zoo) – ‘for any length of time’ Tommy was dressed in clothes to keep him warm and featured in an engraving by ar tist, George Scharf He died from tuberculosis in 1836, just six months after he arrived 3 He was soon replaced by orangutan, Jenny, who was said to be the inspiration for Charles Darwin’s interest in great apes She was one of the first of her species to be displayed in a zoo Jenny was purchased by the zoo for £150 from an animal trader. Ar tists’ impressions of her showed her dressed in clothing. She died some time before 1839, when she was replaced by a ’new‘ Jenny. London Zoo archives document the second Jenny being given cups of tea and having a cap put on her head, which visitors found ’laughable’.4

The first record of a gorilla held in a modern-day zoo dates back to 1876, when a two-year-old male called Mpungu was brought to Berlin Zoo in Germany It is believed that other zoos may have attempted to keep gorillas during the 1800s, however, they died in transpor t or a shor t time (sometimes just days) after their arrival Mpungu was passed from Berlin to London and to Hamburg and died within a year of being sold into the zoo trade 5

The first bir th of a gorilla in captivity did not take place until some 80 years later in 1956, when Colo was born in Columbus Zoo in the United States to wild-captured parents She lived until 2017

As with many wild animals captured from their wild homes for captive display, many – likely the majority – of these early zoo-bound great apes will have died in transit or very shor tly after their arrival Youngsters were preferred by traders as they were easier to handle, but the capture of one individual young primate would almost cer tainly have required the slaughter of several family members as they tried to protect their young from hunters. Youngsters may also have been captured as a ’byproduct’ of the trade in bushmeat, with adults being killed for their flesh, and the babies sold on as ‘pets’ or to zoos.6 Sadly, this scenario continues to play out today

T

L A N D S C A

It is estimated that over 1,500 great apes are currently kept in at least 140 zoos across 28 European countries (Table 1). Germany keeps the greatest number of great apes in zoos, followed by the UK and France, with five European countries keeping more than a hundred great apes in zoos.

Data from 2016, obtained from the Species360 database, provided the (conservative) figure of 3,063 great apes in zoos globally at that time, with 790 gorillas found in at least 122 zoos, 1,612 chimpanzees and bonobos in 188 zoos, and 661 orangutans in 143 zoos These figures only represent data from those zoos that subscribe to the Species360 zoo records database, which is generally limited to accredited zoos or those with greater financial resources 7 As such, this should be considered a minimum rather than a comprehensive inventory

It is likely that European and Nor th American zoos are responsible for keeping the vast majority of great apes 8 Within the UK and the Channel Islands, great apes are currently maintained in 21 licensed zoos, including traditional zoos, a ’rescue centre’ and a ’sanctuary‘ (there is currently no legal licensing distinction between zoos, rescue centres and sanctuaries in the UK) According to available data, in 2024 there were approximately 315 great apes in British zoos, 51 less than in 2014 (Table 2) Zoo surveys conducted by Born Free (previously known as Zoo Check) estimated that there were at least 298 great apes in 29 UK zoos in the early 1990s (chimpanzees ≈ 172, gorillas ≈ 84 and orangutans ≈ 42) Since 2014, the number of zoos keeping great apes has remained fairly constant, with two zoos having ended their keeping of great apes and one zoo acquiring great apes for the first time. 18 of the 23 zoos that have held great apes since 2014 now keep a smaller number.

Africa Alive

Belfast Zoological Gardens

Blackpool Zoo

Blair Drummond Safari Park

Bristol Zoo Project

Chessington World of Adventures

Chester Zoo

Colchester Zoo

Drayton Manor

Dudley Zoo

Edinburgh Zoo

Howletts Wild Animal Park

Jersey Zoo

Longleat Safari Park

Monkey World*

Paignton Zoo

Por t Lympne Wild Animal Park Twycross Zoo

Ape & Monkey

Zoo

Table 2: Overview of great apes in premises holding a zoo licence in the UK and the Channel Islands over time

‘Rescue Centre’

chimpanzee

however

is believed to par ticipate in orangutan

G O R I L L AS

The European Association of Zoos and Aquaria (EAZA) Ex situ Programme (EEP) for gorillas is managed at the subspecies level for the Western Lowland Gorilla (Gorilla gorilla gorilla) In 2021, a total of 485 gorillas were registered within the EEP, including animals in European zoos and zoos located in other regions Of those animals, 8% (approximately 39 individuals) are recorded as wild caught 10 It is only in the last 30 years that captive-born individuals have outnumbered those which are wild caught UK zoos currently keep more gorillas than any other country in Europe (Table 1)

Some published data suggests that improvements in husbandry over time have increased longevity for gorillas in zoos. Maximum longevity for gorillas in captivity repor tedly increased by 62% to 54 years in the 30 years to the end of the last century.11 However, this data is misleading While maximum longevity may be significantly higher, the average age at death for gorillas in zoos sits at around 26 (median) – 30 (mean) years old It has been

suggested that, while life expectancy for gorillas in the wild is between 30-40 years old, in human care some individuals may live into their 50s or 60s.12 While this may technically be true, it is impor tant to remember that 76% of the gorillas who died in zoos during the period covered by the study were less than 30 years old

Only seven individuals (0 8%) in the historic captive population of gorillas are repor ted to have lived beyond the age of 50 and only two (0 2%) beyond the age of 55 The oldest gorilla on record lived to be 64 years old Within the EEP, it is repor ted that only 40 females and 20 males have ever lived beyond the age of 40.10

The EEP currently aims to reduce breeding and maintain the current population level due to the lack of available space for additional individuals in zoos keeping gorillas, and the fact that many facilities are unwilling to house male gorillas 10

C AS E S T U DY: M ASS A

Massa, a male Wes tern Lowland Gorilla, was born in Central Africa in 1971. He was taken from his wild family as an infant and in 1975 was transpor ted over 3,000 miles to Krefeld Zoo in Germany, where he was incarcerated for t he next 45 years.

Massa was the first resident of Krefeld Zoo’s new tropical ape house, which was said, at the time, to be ‘state-of-the-ar t’ in its construction and how it would house the animals. However, it did not provide the animals with any outdoor space A few months later, Massa was joined by two young female gorillas named Boma and Tumba, who had also been taken from the wild

After being fed a mixture of baby food, vegetables and fruit, Massa repor tedly grew quickly He once managed to escape his enclosure when the zoo was closed to the public A keeper, Klaus Reymer, described finding Massa sitting by his enclosure trench, howling a ‘hear tbreaking cry’. Reymer used to cuddle and tickle Massa, dedicating time to play with him and be his ‘substitute family’. Several keepers would regularly enter the enclosure with the gorillas. However, in 1978, Massa blocked Reymer’s exit from the enclosure 13 Reymer said that ‘Massa didn’t move’ except to take a step towards him Reymer managed to get out, but the zoo changed its policy as a result of the incident, and thereafter nobody was permitted to enter the enclosures with the gorillas

Massa apparently developed a fear of people wearing masks, face paints or cer tain hats On seeing such visitors, he would apparently ‘flail his hands against the walls of the enclosure, tear out hair and bite his arms ’ This led to the zoo putting up a sign asking visitors adorned in this way not to visit the gorilla enclosure Zookeepers described Massa as having ‘quirks’ and was ‘choleric’ or irritable He would chase, beat and bite the females. He would also throw food and excrement at visitors 13

In 1978, at the age of seven, Massa impregnated Tumba, but she miscarried. After three fur ther miscarriages over the following two years, she was temporarily put on bir th control medication In 1981, Tumba gave bir th to the then 10-year-old Massa’s son, but he died 11 months later from a ‘skull injury’ In the same year, Boma also gave bir th to another son fathered by Massa and named Gorgo Over the next 11 years, Massa would go on to father six more babies with Boma, two of whom

were stillborn, and four more babies with Tumba, two of whom died within a year. In 1996, Massa fathered his last baby with captive-born Oya, who had been brought in from Zurich Zoo in 1994.14 This baby was stillborn (Figure 1)

Massa’s demeaner was said to have improved during this period He was described as being ‘like a different person’, lovingly interacting and playing with his offspring 13 Krefeld Zoo gradually transferred Massa’s surviving offspring to other zoos, whilst also creating a new breeding group of gorillas brought in from various other zoos, and constructing a new exhibit called ‘Gorilla Garden’ With Massa now infer tile, the zoo kept him in with Tumba and Boma, creating a separate senior group in the old ape house.15

In 2000, Massa’s appetite repor tedly deteriorated. He was found to have high inflammatory values in his blood. A variety of medication was administered, including penicillin Although his medical condition was said to improve, his bad temper returned He would throw things at visitors and in the evenings would repeatedly rub his forearms necessitating the administration of painkillers A glass screen was also constructed, which was eventually covered, so that he could no longer see out As he aged, Massa developed diarrhoea, pancreatic problems, and began losing muscle mass 13

In 2019, female Tumba died suddenly, aged 45 When announcing her death, Krefeld Zoo said that Massa and Boma were ‘mourning their companion’.16 On New Years Eve 2019, tragedy struck when a fire, star ted by a candle-lit sky lantern that had blown in from nearby, destroyed the old monkey and ape house With no outside enclosures to escape to, the animals were trapped inside Over 30 animals died, including five Bornean orangutans, one western chimpanzee, and gorillas Massa and Boma

As people mourned this tragic loss of life, more details began to emerge regarding the animals’ final moments Whilst it was repor ted that all animals had either burned to death or been killed by inhaling toxic smoke, it was later revealed that two chimpanzees had miraculously survived with only minor burns. Rescuers searching through the charred remains the next day found a badly injured orangutan, who was euthanised by a veterinarian. 49-year-old Massa was also found alive He was horrifically burned but the vet was unable to relieve his suffering due to the state of his skin and body Massa had to be shot by a police officer using a submachine gun 17

Following the fire, concerns were raised about how quickly the fire had spread and why there was no sprinkler or fire alarm systems in place Krefeld Zoo stated that these were not required when the building was built in the 1970s 18

Figure 1: The fate of Massa’s offspring with Tumba, Boma and Oya, as of June 2025

C H I M PA N Z E E S

There are more chimpanzees kept in European zoos, and more zoos keeping them, than any other great ape species UK zoos are believed to house more chimpanzees than any other European country, followed by Germany and France (Table 1) This is mainly due to 54 chimpanzees currently housed at a ‘ rescue centre’ who are managed as four independent groups 19

The life expectancy of chimpanzees in zoos has increased over time However, as for gorillas, the average age at death remains below best estimates of life expectancy in the wild. The average age at death in Nor th American zoos was found to be 21 years for captive-born male chimpanzees and 27 years for captive-born females 20 A Yale University study cited average life expectancy of free-living chimpanzees in “favourable ecological circumstances” to be 32 8 years 21 Given that free-living chimpanzees are subject to external pressures such as environmental degradation, competition for food, and hunting, as well as an absence of veterinary care in the case of illness or injury, one might expect life expectancy in zoos to be higher by comparison

The chimpanzee EEP focuses on two subspecies (P. t. verus and P. t. troglodytes).22 However, the current EAZA Best Practice Guidelines include a

long-term moratorium on breeding, which is likely due to limited space and a lack of clarity over the genetic ancestry of the European zoo population (see section on Hybridisation of Great Apes in Zoos) Zoos across Europe continue to breed chimpanzees, although whether these bir ths are intentional or accidental is unclear

Many female chimpanzees in European zoos were born in circuses, laboratories, private collections, zoos with small groups, or hand-reared 19 Older females, still in zoos today, were primarily wild-caught at a very young age. Zoo-bred chimpanzees frequently experience high levels of stillbir ths, neonatal deaths and maternal neglect as a result of a lack of alloparenting experience within zoo chimpanzee groups (i e looking after other parents’ young) when compared to wild chimpanzee troops (see section on Social Structure)

EAZA documents indicate that a number of zoos across Europe are ending their par ticipation in the breeding programme and are no longer keeping or wish to keep chimpanzees, resulting in significant rehoming challenges 19 In the ten years since 2014, the number of chimpanzees in UK zoos has decreased by over 25% from approximately 187 to 137.

C AS E S T U DY: S A N T I N O

Santino t he chimpanzee was born at Hellabrunn Zoo, Germany, in 1978, where he repor tedly didn ’t integrate well wit h ot her chimps.23

When he was four years old, Santino was transferred to Furuvik Zoo, Sweden, where he was later joined by Linda, a young female chimpanzee who had been orphaned in the wild in Liberia

They became ‘siblings’, developing a strong bond He was also joined by two chimpanzees transferred from Kolmården Zoo, Sweden: Manda, who was orphaned when her mother died, and Selma who had been rejected by her mother. Another female, 5-year-old Maria Magdalena, arrived in 2005 from Borås Zoo, Sweden.

Santino was described as ‘thoughtful’ and ‘levelheaded’ by his keeper 23 However, some of Santino’s observed behaviour over the years was unusual In 1994, soon after he became the dominant male chimp at Furuvik Zoo, Santino star ted angrily throwing stones at zoo visitors

Early in the morning, Santino would calmly collect stones and lumps of concrete from around his enclosure and cache them neatly in piles, so that he had them to hand ready for opening time and the arrival of visitors some hours later 24,25 This behaviour attracted the attention of Mathias Osvath, a cognitive zoologist and primatologist from Lund University, who studied Santino’s behaviour for over a decade and published a repor t in 2009 26 He stated that ‘such planning implies advanced consciousness and cognition traditionally not associated with animals Many animals plan, but this is planning for a future psychological state That is what is so advanced ’

Craig Stanford, co-director of the Jane Goodall Research Center at University of Southern

California, considered that Santino’s behaviour may have been as much ‘ a sign of boredom as intelligence’ , spending ‘his whole life in a small enclosure with very few outlets for his creativity ’ 26

In Autumn 2008, the zoo’s management took the decision to castrate 30-year-old Santino in a bid to try and stop his stone-throwing and agitated behaviour, hoping that the resulting reduction in hormones would calm him down. In 2015, in response to visitor concerns about Santino’s poor physical condition, the zoo’s Animal Manager stated that, since his castration, he has ‘gradually lost much of the significant musculature of a male chimpanzee’, but that he continued to be ’ a lively, happy and resourceful 37-year-old chimpanzee who shows leadership, tenderness, patience ’27 Four months earlier, a new 12-yearold male chimp named Tjobbe arrived at Furuvik Zoo At this time, Santino was living with Linda and Selma Tjobbe was placed in another section with Maria Magdalena and Manda 28 In 2019, Torsten was born to Maria Magdalena and Tjobbe, the zoo’s first chimp bir th in 25 years.23

In December 2022, tragedy struck when Santino, aged 44, along with Linda, Manda, and Torsten, were shot dead after they escaped from their enclosure at Furuvik Zoo (see Captivity Related Injury, Illness, and Death of Great Apes) The incident was described by national media as the “Massacre in Furuvik” and the “Furuvik Bloodbath” 29,30

In 2024, the global zoo population of orangutans was repor ted to be 875 individuals (577 Bornean and 298 Sumatran), with over 300 orangutans kept in European zoos (Table 1). In contrast to chimpanzees and gorillas, the number of orangutans in UK zoos has increased since 2014 (Table 2)

In the wild, orangutan lifespans average 35-40 years, although individuals can live into their 50s and females continue to breed into their mid-to-late 40s 31,32 A 2009 study repor ted that the median lifespan of captive-raised Sumatran orangutans was 24 6 years 33

Orangutans experience the longest interbir th interval of all mammals with infants not reaching independence until around the age of eight.34 This results in very high rates of survival in preweaned individuals. In contrast, zoo-housed orangutans experience higher infant mor tality despite being free from predation and being

provided with food and veterinary care.35 Zoo-housed females have shor ter interbir th intervals than would typically be experienced in the wild and commonly die at a younger age.36

In 2018, it was repor ted that 51% of the EEP orangutan population were Bornean, 44% were Sumatran and 5% (18 individuals) were hybrids 36 However, the number of hybrids may be an underestimate as knowledge gaps remain relating to the genetic ancestry of zoo-housed orangutans, par ticularly in relation to the degree of hybridisation since the reclassification of the Tapanuli orangutan as a separate subspecies in 2017 7

Molecular DNA analysis under taken to date has identified few captive orangutans of pure Tapanuli lineage, leading researchers to the conclusion that any zoo population is currently too small to suppor t a sustainable and genetically viable captive population for the species 7 O R A N G U TA N S

C AS E S T U DY:

M U J U R

In 2005, female Bornean orangutan, Mujur, was born at Dublin Zoo in Ireland to 22-year -old Maggie and 10-year -old Jorong. They lived toget her wit h t wo ot her females, Leonie and her daughter Riona. A mont h af ter t he bir t h, t he zoo said bot h youngs ters were t hriving and inseparable.37

In April 2008, Maggie managed to climb out of her enclosure, leaving infant Mujur behind. She spent an hour wandering around before zookeepers managed to shoot her with a tranquilliser dar t gun and recapture her 38

In July 2008, Maggie died unexpectedly from a respiratory infection At that time, Mujur was just shor t of her third bir thday In the wild, orangutan babies are usually dependant on the mothers for food and travel until they are two-and-a-half years old and usually stay with their mothers until the age of six to eight years, so the orphaning of Mujur at such a young age was a concern. She significantly increased the time she spent in close physical contact with Leonie, who became her foster mother. Leonie allowed Mujur to sleep in the same nest with her and to suckle from her, even though she was not lactating 39

Being par t of the orangutan EEP, Dublin Zoo said that they were hoping that Sibu, a male who arrived in 2008 from Rhenen Zoo in the Netherlands, would breed with Leonie They were also hopeful that Sibu would breed with Mujur 39 In 2019, and again in 2022, Mujur repor tedly gave bir th Both babies are believed to have died shor tly after bir th, most likely due to Mujur not having the ‘ necessary maternal qualities’ to successfully nurse her young.40

In February 2024, Sibu died aged 45, from a cardiac and respiratory condition However, before he died, he had impregnated Mujur for the third time and she gave bir th to a son on 31st

July 2024 who the zoo named Sibu Jr (’SJ’).41

Prior to the bir th, pregnant Mujur was shown videos of other orangutans nur turing and feeding their babies in an attempt to try and prevent another baby’s death The zoo also brought in 30 human mothers to show Mujur how to breastfeed However, despite appearing to be extremely interested in watching the women feed their babies through the glass and showing ‘good maternal care’ after bir th, she repor tedly did not hold SJ in the correct position 42

SJ was separated from Mujur, and the zoo took the decision to begin bottle-feeding him rather than ‘letting nature take its course’ as they had done previously. The zoo described the late Sibu’s genetic profile as extremely impor tant for the European breeding programme and were keen to see his legacy live on through SJ However, hand-rearing an infant orangutan until independence was not a long-term option at Dublin Zoo In October 2024, after months of hand-rearing, SJ was transferred to Monkey World in the UK, which has a nursery for captive infant orangutans who have been orphaned or rejected by their mothers 43

With the death of 28-year-old Riona at the end of June 2024, Mujur and Leonie became the only surviving orangutans at the zoo. In April 2025, 44-year-old Leonie also died. With Mujur now alone, the zoo stated that they were focusing on ‘carefully planned introductions to ensure Mujur has companionship in the months ahead’ 44

An international studbook for bonobos has been maintained at Antwerp Zoo, Belgium, since 1974

In 1989, in recognition of the ‘small’ population sizes within both the EEP and equivalent Nor th American Species Survival Plan (SSP) programme, the zoo industry decided to form a global breeding programme combining the regional programmes of Europe and Nor th America.45 This decision has resulted in individuals being transpor ted between continents over the subsequent decades. The

current global zoo population is believed to have descended from just 36 founder animals 46 There are estimated to be 11 zoos within six European countries keeping bonobos, including one in the UK (Table 1) German zoos currently keep almost 50% of the bonobos within European zoos Due to their low representation in European zoos there is less information on this species than for the other great ape species.

S U M M A RY

• Zoos are unable to replicate the dynamic social structures of great apes such as fission-fusion societies or the dispersal of individuals to form new families.

• Unnatural social structures result in increased conflict, neonatal deaths and still bir ths, as well as infant rejection and death.

• European breeding programmes acknowledge that zoos are struggling to house increasing numbers of male great apes, with ‘surplus’ individuals facing an uncer tain future

• Mental distress among captive great apes commonly manifests in stereotypic behaviours

• Zoo guidelines currently advocate the use of pharmacological treatments to alleviate signs of stress in great apes

• Unsuitable enclosures and climatic conditions can result in obesity, unnatural behaviours and health problems

All non-human great apes are considered to be highly intelligent. They are tool users, they have a concept of self, and there is evidence to suggest that they can plan ahead and thus conceptualise their future. These, among other attributes, present significant welfare challenges for those individual great apes forced to live in captivity Instead of the complex, dynamic, and ever-challenging physical, environmental and social conditions that great apes experience in their natural habitats, those kept in zoos experience limited, largely unchanging, and relatively small living conditions throughout the entirety of their lives and, most impor tantly, lack autonomy

S O C I A L S T R U C T U R E

Zoos necessarily impose on great apes a lack of social oppor tunities, unnatural and often forced mating experiences (including invasive ar tificial insemination), an inability to mimic the dynamic fission-fusion social groupings common to chimpanzees and bonobos, and an inability to escape conflicts, sometimes resulting in injury or death

Complex, fission-fusion societies simply cannot be replicated in zoos.

In their natural habitat, bonobos, chimpanzees and, to a lesser extent, orangutans, form what are known as fission-fusion societies.46 This means that, while they form par t of an overarching community, individuals split and merge into subgroups and move between them. The splitting and merging of groups will be influenced by various factors including personal relationships and hierarchies, family ties, conflicts, resource availability, and habitat fragmentation, among others Inherent to a fission-fusion society is individual choice

This dynamic social structure simply cannot be replicated in captivity, despite claims by zoos that it can Any suggestion that the daily organisation of a captive group of great apes into two or more sub-groups dictated by zoo staff is an example of fission-fusion is disingenuous and highlights the zoo industry’s inability to provide the great apes in their care with natural social oppor tunities Indeed, zoo industry guidelines acknowledge that the current keeping practices of orangutans in zoos do “not sufficiently reflect their social structure in the wild”, due to their inability to replicate fission-fusion social dynamics 36

In gorilla society, both sexes commonly disperse from their natal group At around the age of 11, males may leave their natal group and temporarily form a bachelor group with other young males until they can compete for females.47 From the age of eight, females may leave to join another group or a solitary silverback.48 Such transfers usually occur when groups or individuals come into close proximity. This natural dispersion cannot be replicated within a traditional zoo environment.

Rather than replicate natural social structures, the grouping of great apes in zoos will typically be dictated by space limitations and the zoo’s breeding programmes In practice, the ‘ one male’ approach is still predominantly adopted by zoos with chimpanzees despite recognition that wild chimpanzee troops consist of multiple males and females 22 As of November 2024, we estimate that at least 37 European zoos keep one male or no males at all In the wild, chimpanzee groups operate at a community level, which can exceed 100 individuals, and at the par ty level Multiple par ties make up a community, with par ties consisting of six individuals, on average 49 EAZA guidelines do not currently recommend a specific group size, whereas the Association of Zoos and Aquariums (AZA) in Nor th America, recommend a minimum group size of eight animals (three males, five females) 50 Just 34% of European zoos assessed as par t of this repor t house eight or more chimpanzees and only 18% have ≥8 individuals and a group consisting of an equal (± 2) number of individuals of each sex However, it is unclear if all individuals are maintained collectively or across more than one enclosure where they are physically isolated from each other. Many facilities simply do not have the space to accommodate groups with equal numbers of both sexes or in conditions which replicate par ty sizes in the wild or facilitate their collective formation into communities.

Concerningly, at least three European zoos are keeping a solitary chimpanzee, four zoos are keeping a single orangutan, and one zoo is keeping a gorilla on his own Such situations may have resulted from the deaths of other great apes or some other historical event, the zoo may intend phasing the species out of its collection, or veterinary and other considerations may deem it in the best interest of the health of that animal for he or she to be kept alone What is clear, however, is that such situations almost exclusively arise as a result of their perpetual confinement

Unnatural social structures can also have knock-on effects which may result in severe social disorders such as the rejection and/or mutilation of infants 22 The frequency of maternal neglect in zoo-housed gorillas is considered to be significantly higher than that in the wild Individuals who have not had the oppor tunity to observe or par ticipate in maternal behaviours, or those who have been hand-reared, have been found to be significantly more likely to reject or neglect their young.51 High numbers of stillbir ths and neonatal deaths are also seen in zoo-housed chimpanzees where younger mothers lack experience of maternal care and when tension within the group is high.22 The neglect of offspring by low-ranking females may be due to their lack of ability to separate themselves from higher ranking individuals, as they would in the wild due to fear of infanticide 52

‘S U R P L U S’ I N D I V I D UA LS

The social structures of great ape families and communities are complex and extensive as highlighted above In captivity however, social choices and the selection of mates are controlled, resulting in captive management methods which can be detrimental to individuals 53 Those who are determined to be less genetically desirable are often deemed ‘surplus’ This ignores the reality that in the wild there is constant competition between males, and in some cases females, for dominance Indeed, some males will never become the dominant individual and may not get the chance to pass on their genes Never theless, these individuals still play a fundamental par t in the function of great ape societies in the wild. Such social dynamics are severely limited in captive zoo environments. Zoos and zoo breeding programmes commonly place greater moral value on the species as a whole than on individual animals. By their very design, zoos are limited in the number of species or individual animals they can keep. Also, the species they keep varies from zoo to zoo This often results in some zoos having too many animals, some of whom face an uncer tain future

The EAZA orangutan EEP acknowledges that European zoos have a ‘male surplus problem’ ©

Current sex ratios in gorilla breeding programmes in Europe and Nor th America are close to equal, however natural groups consist of multiple females to one or a few males This creates significant issues when young males begin to mature and potentially challenge their father or the dominant male due to the potential risk of inbreeding if they were to become the alpha male The issue is exacerbated by the confines of zoo life as they are unable to disperse and find another group of females as they would in the wild Additionally, most zoos will already have a male within their collection, resulting in many male gorillas being deemed ‘surplus’ An alternative approach is to castrate male gorillas.

In 2021, leaked documents repor tedly revealed that EAZA were considering adopting a strategy of culling healthy male gorillas due to overcrowding.54 The gorilla action plan, released to stakeholders in zoos, repor tedly stated that culling would be “the most appropriate tool if strictly talking from the biological point of view,” but that the decision could be unpopular with the public EAZA later denied the existence of such plans However, they did later publish a generic position statement on culling in 2023 which relates to the captive management of all species kept in EAZA zoos,55 within which EAZA consider culling to be “standard operating procedure” where:

i The animal poses a serious and unavoidable threat to human safety

ii An animal’s pain and/or stress cannot be adequately alleviated

But culling is also deemed appropriate where:

i. The animal’s permanent relocation would be to a facility or accommodation which “cannot assure a proper level of welfare for the animal”.

ii. The animal’s presence is “unreasonably disruptive” to the dynamics of a social group.

iii. The animal’s presence puts the maintenance of a population’s “demographic or genetic viability” at risk.

Castration is currently recommended for gorillas considered by the zoo industry to be “genetically surplus” 10 Castrated young males do not develop secondary sexual characteristics Current EAZA Best Practice Guidelines state their desire to control the sex ratio of gorillas in zoos through “ ar tificial insemination with sex-sor ted sperm and selective abor tion of foetuses”

The EAZA orangutan EEP acknowledges within its Best Practice Guidelines that European zoos have a “male surplus problem” 36 This issue is also reflected in Nor th American zoos, where sex ratios are close to 50:50 Whilst bachelor groups have been established for captive gorillas and chimpanzees, attempts have been less successful in orangutans due to the aggressive behaviour of adolescent and sub-adult males This is despite unflanged males commonly being accepted in the wild home ranges of flanged males Flanged males are

recognised by large cheek pads on the sides of their face, plus a large throat sac, in contrast to unflanged males who, while also being sexually mature, lack these physical traits.

For chimpanzees, European zoo guidelines state that the EEP has to deal with large numbers of males which are deemed ‘surplus’ The reasons provided include limited space, a preponderance of male bir ths in some facilities, non-breeding males becoming dominant over a male selected by the zoo for breeding, and adolescent males becoming problematic at an earlier stage due to the lack of natural group dynamics where mature individuals would asser t authority and keep younger males in check 22

In species which have complex social structures, like great apes, “individuals are repositories of social and practical knowledge for their groups and they provide social and behavioural stability” 56 To consider any individual, the result of an intentional captive breeding programme, as ’surplus’ is ethically indefensible, highlights the unsuitability of keeping these species captive, and undermines one of the main claims made by zoos – that they provide the highest levels of animal welfare for their charges

S T E R E O T Y P I E S

Poor welfare frequently leads to mental distress in these complex animals, which can manifest in abnormal ‘zoochotic’ (stereotypical) behaviours Such behaviours may include excessive grooming and self-mutilation, food-based stereotypies (such as regurgitation and reingestion), coprophagy (eating their own faeces), pacing, rocking, digit sucking, self-grasping, and extreme aggression or submission Some of these behaviours are described as ‘natural’ by zoos since they are commonly observed in a zoo environment, but this is misleading as these behaviours are extremely uncommon - and often undocumented - in the wild 57 Where such behaviours have been observed in the wild, the frequency at which they occur in captivity is much higher

Research has suggested that “ a substantial number of great apes in captivity show behavioural abnormalities and measurable signs of distress ”58

Mental distress in captive great apes can manifest in ‘zoochotic’ behaviours, such as coprophagy (eating their own faeces).

In some situations, the presence and proximity of zoo visitors has been shown to have a negative effect on great apes, increasing stress and the frequency of stereotypic behaviours.59

In the most extreme cases, pharmacological treatments are used in an effor t to ameliorate captivity-related mental illness The use of anti-depressants within the zoo industry has increased markedly in recent years In the late 1990s, Dr Hayley Murphy, the Head Veterinarian of Franklin Park Zoo in Boston, Massachusetts, and Psychiatrist, Matthew Mufson, surveyed zoos with gorillas to better understand their use of psychopharmaceuticals Half of the 31 zoos that responded to their survey confirmed that they had provided psychopharmaceuticals to their gorillas 60

EAZA veterinary guidelines for great apes outline and advocate the use of neuroleptics and antipsychotics in great apes who are demonstrating signs of aggression or stress, and par ticularly in gorillas The medications used are the same as those used as antidepressants in humans e g citalopram, fluoxetine (Prozac) and clomipramine 61

In their natural environment, the home range, daily travelling distance and habitat use of great apes vary significantly between and amongst groups in response to food availability or scarcity, competition, and seasonal changes to their habitats (Table 3) This is par ticularly the case for chimpanzees who are the most widely distributed great ape and therefore inhabit the greatest variety of habitat types 62 African great apes also employ dietary switching behaviour in response to staple dietary foods becoming depleted or unavailable 63

For great apes in the wild, the primary motivation for travel is food acquisition and territorial defence, with chimpanzees spending 30 – 40% of their time travelling 64

In zoos, the motivators for travel are either catered for or managed (scheduled feeding) or removed (no territorial disputes due to enclosure boundaries) Additionally, the size and quality of the captive environment may obviate the need for, severely restrict or nullify travel. This creates significant gaps in the natural activity budgets of great apes in zoos which can result in the manifestation of stereotypies (see above) or health conditions (see below).

Home Range

Bonobo

Chimpanzee

Gorilla

Orangutan

2 – 22km2 64

2 8 – 62 2km2 64

7 – 14km2 (Western lowland) 67

Females

Bornean: 3 5 – 6km2

Sumatran: 8 5km2

Males, less studied, but believed to be larger

Sumatran: 25km2 69

Comparative Size

City of London: 2 9km2

Isles of Scilly: 16km2

Bournemouth: 46 2km2

Heathrow Airpor t: 12 3km2

Gibraltar: 6 8km2

Avg 1 2km

Range 1 – 4 2km 65

2 – 4km 66

Avg 0 5 – 2km 5km+ observed 68

Avg 0 79km

Watford: 21 5km2 Daily Travel Dis tance

Range 0 09 – 3 1km 69

Zoo enclosures are many magnitudes smaller than the natural home ranges for great apes and lack the environmental complexity that these species have evolved to live with The wild ranges of great apes are estimated to typically exceed the size of great ape zoo enclosures by a factor of 20,000 64 This can have serious detrimental consequences for the health of great apes held in zoos Zoo industry guidelines recognise that it is “difficult to encourage gorillas to exercise in a confined area such as a zoo enclosure”, which can result in individuals becoming obese.10 Even those facilities built in recent years, or still under construction at the time of writing, fail to provide for the par ticular requirements of these complex animals.

Taxa

Table 3: Home ranges and the daily travel distances of each great ape taxa

©

The average monthly temperature at most zoos across Europe is less than 10°C for at least half the year, resulting in limited outdoor access.

A new orangutan house that opened at Dresden Zoo, Germany, in 2024 has a building volume of approximately 21,173m³ and a useable area of approximately 2,095m², or less than half a hockey pitch (5,000m2) 70 While a significant improvement on their previous out-dated orangutan enclosure, the new useable space is still over 1,660 times smaller than the smallest recorded wild orangutan home range The construction cost approximately €22 million (£18 5 million) In contrast, in 2023/24, Wildlife Conservation International’s Orangutan Project protected 12,502 orangutans and 7,720km2 of rainforest, employed 218 wildlife protection rangers, rescued a fur ther 52 orangutans and released or relocated another 40, for less than a quar ter of the cost of Dresden’s orangutan enclosure ($5 6 million (£4 2 million)) 71

In 2021, Prague Zoo, Czechia, opened their new gorilla exhibit.72 According to their website, the breeding group has an indoor area of 465m2 and an outdoor area of 2,570m2, while the non-breeding group has an indoor area of 120m2 and an outdoor area of 356m2. For the non-breeding group, the combined space is over 14,000 times smaller than the smallest home range of free-living western lowland gorillas. The construction cost 267 22 million Czech Koruna (approximately £9 million) 73 In contrast, in 2024, the Gorilla Rehabilitation and Conservation Education Centre (GRACE) protected 2,000km2, operated the only sanctuary for Grauer’s gorillas in the world in the Democratic Republic of Congo, and later successfully returned four sanctuary housed females back to the wild, at a cost of $2 3 million (£1 7 million) 74

The building and renovation of zoo enclosures housing great apes in the UK are estimated to have collectively cost approximately £63 million since 2007 This includes the £18 million funding Twycross Zoo received from the government in 2023 for a National Science and Conservation Centre housing great apes, which will cost £25 million in total Despite this expenditure, as recently as 2022 a zoo inspection repor t for Blackpool Zoo, UK, stated that the “orang[utan] outside enclosure and the primate house are small and outdated ”

Gorilla conservationists have expressed frustration over the inordinate amounts of money invested by zoos in holding great apes captive. In 2007, when London Zoo invested £5.3 million on a new gorilla exhibit, gorilla exper t and United Nations’ Chief Consultant on Great Apes Ian Redmond OBE said: “£5m for three gorillas [seems a huge amount] when national parks are seeing [three gorillas] killed every day for want of some Land Rovers, trained [people] and anti-poaching patrols It must be very frustrating for the warden of a national park to see” 75 In 2024, London Zoo submitted a new planning application to extend the two outdoor enclosures and reconfigure the internal housing of the gorillas, as the existing enclosures were no longer compliant with EAZA standards or the anticipated revised British zoo standards (see Legislation) 76

Enclosure size and construction has a direct impact on ape welfare in zoos In 2012, Tatu, a five-year-old gorilla at Prague Zoo, Czechia, accidentally hung himself from a rope in his enclosure 77 The oldest female, Kamba, refused to leave Tatu, which prevented the timely intervention of zoo staff Other negative impacts include the inability of great apes to demonstrate natural behaviours, and the prevention of adequate physical movement resulting in obesity and other health issues Being forced to live in close proximity with conspecifics can create social tension and increase the chance of conflict and resulting injuries, as well as exacerbating the potential for disease spread between individuals. All of these factors negatively impact the mental and physical health and welfare of animals.

Great ape housing in zoos, which are, after all, public display facilities, is designed to ensure that the public can see the animals, often both when they are inside and outside, offering zoo apes little or no respite from public gaze

In addition to size limitations, great ape housing in zoos is often designed primarily for the convenience of the zoo’s management For example, in a 2021 study of AZA-accredited zoos in Nor th America, 29 of the 42 surveyed zoos (69 05%) were found to exclusively house their apes on hardscape floors such as concrete 78 This is likely because concrete is easier to clean than more complex, natural substrates In contrast, deep-litter bedding or ‘biofloors’ (which are higher maintenance) are considered by some zoo professionals to be more naturalistic, and to promote species-typical behaviour, minimise impacts on joints, reduce the likelihood of bacterial survival and disease transmission and reduce respiratory issues due to greater control over humidity.78 Despite apparent health and welfare benefits of biofloors, many zoos still utilise hardscape floors.

Although gorillas live primarily on the ground, they are still repor ted to spend 5-20% of their day in trees. For chimpanzees this increases to approximately 50% of the day off the ground, while orangutans are almost 100% arboreal 10 Zoos often argue that less space and complexity is required for their animals as the resources they need are provided within their captive environment However, it is impor tant to consider how the captive environment alters an individual’s behavioural reper toire in ways that could potentially negatively impact their health and promote maladaptive behaviours that would have implications if they were to ever be reintroduced to the wild For example, arboreal travel oppor tunities for orangutans are severely limited in captivity, which not only reduces their spatial abilities, but has also likely resulted in morphological differences between the musculoskeletal systems of captive and wild orangutans 79 It is commonplace to see an orangutan on the floor of its enclosure within a zoo, which represents an unnatural state Zoo environments also typically lack appropriate oppor tunities for great apes to learn how to build nests, recognise and extract wild edible food, and assess danger 80 Captivity is also likely to increase familiarity with humans.

The cooler climates experienced by many zoos across Europe may also limit the willingness of great apes to access their, often larger, outdoor enclosures. The average monthly ambient temperature at more than half of the institutions across Europe keeping great apes is less than 10°C for at least half the year

A survey of zoos keeping gorillas as par t of the EEP found that 50% of zoos were keeping their gorillas inside without outdoor access for an average of 15 hours per day from Spring to Autumn 10 This time period is likely increased over winter when it is colder Less than half of the zoos surveyed provided their gorillas with 24-hour outdoor access

This lack of outdoor access can have knock-on effects for the health of captive great apes Climatic conditions which severely limit outdoor access, par ticularly in nor thern European countries, can result in insufficient exposure to UV light, potentially resulting in vitamin D3 deficiency 10 Ar tificial UV lighting may address this deficiency to an extent However, it was stated at a 2022 EAZA conference that 90% of a subset of European zoos were found not to be providing UV to their great apes, apparently due to financial constraints.81

C A P T I V I T Y R E L AT E D I N J U RY, I L L N E SS , A N D D E AT H O F G R E AT A P E S

S U M M A RY

• Zoo diets are incomparable to those in the wild, with animals lacking natural foraging and behavioural oppor tunities, which can result in obesity and other nutritional diseases

• Hear t disease is a leading cause of death in captive great apes and is linked to obesity and chronic stress.

• Captive great apes are highly susceptible to various infectious diseases in zoos, with some being fatal, due to their close genetic relationship with humans

• An inability to escape conflict due to the confines of captivity has resulted in the serious injury or death of many great apes in zoos

• Where great apes have escaped their zoo enclosure, human injury and the killing of the animal(s) are common outcomes

D I E T A N D O B E S I T Y

In the wild, great apes predominantly consume a diet consisting of low-fat, high-fibre, and very-low cholesterol browse and forage.82 Diets in zoos frequently struggle to replicate these requirements and often include higher quantities of cultivated fruits which are typically higher in sugar and lower in dietary fibre compared to wild fruits. Such diets can have negative impacts on the physical health and behaviour of captive primates 83 Not only are zoo diets often incomparable to diets in the wild; but foraging (selecting from a wide variety of plant species) and feeding behavioural oppor tunities (preparing the edible par ts and discarding the rest) are also lacking in captive environments

Zoo industry guidelines acknowledge that providing adequate quantities of browse for gorillas and replicating the feeding ecology of orangutans is difficult for most zoos to achieve A survey of European zoos published in 2024 found that just 53% provided browse for their gorillas 10 The zoo industry also recognises that many zoo-housed gorillas are overweight, while 54% of orangutans within the European breeding programme were found to be overweight or obese 10 Type II diabetes is associated with obesity and is the most common form of diabetes seen in captive chimpanzees and orangutans 84 Obesity in captive orangutans can contribute to fatal acute respiratory distress syndrome during anaesthesia 36

As with humans, all apes can suffer from various forms of ar thritis, although chimpanzees and gorillas are par ticularly vulnerable. Factors which contribute to osteoar thritis in humans, such as injury, obesity, and a sedentary lifestyle, may also result in similar outcomes for captive apes.85

D I S E AS E A N D I L L N E SS

Cardiovascular Disease

Hear t disease is a leading cause of death among captive apes in both zoos and laboratories One study found that 45% of bonobo, 41% of gorilla, 38% of chimpanzee, and 20% of orangutan deaths in captivity resulted from cardiovascular disease 86 Correlations have been found between hear t disease and obesity, as well as chronic stress in captive apes 45 Hear t disease is repor ted to be “nearly absent in wild populations”, with cardiovascular diseases being identified during post-mor tems in 3% of wild mountain gorillas (Gorilla beringei beringei ) and 18% of wild chimpanzees (Pan troglodytes schweinfur thii ) suggesting that captivity is a defining factor in its development in great apes held in zoos 87,88 In March 2025, a male chimpanzee called Tombe died of a suspected hear t attack at the age of 28, less than a month after being transferred from Colchester Zoo in England to Belfast Zoo in Nor thern Ireland.89

Infectious Diseases and Zoonoses

Because of their close genetic relationship with humans, their complex social structures and behaviours, and the stress they endure in captivity, captive great apes are highly susceptible to various infectious diseases in zoos

Notwithstanding any effor ts by zoo management and staff to maintain good hygiene and sanitation, the inherent problem of having different species in close proximity, in small unnatural environments and under stressful situations, is a recipe for disease transmission between those species and humans.

Respiratory infections are common, and upper respiratory tract infections can spread quickly between animals and can lead to serious secondary complications such as pneumonia, which can be extremely challenging to treat successfully Human respiratory viruses such as influenza, respiratory syncytial virus (RSV), and coronaviruses such as Covid-19, can all affect great apes 90 Upper respiratory tract disease is a significant cause of morbidity in captive orangutans, which can be fatal, par ticularly if it affects the laryngeal air sacs which play a role in vocalisation, although the pathogenesis (i e the way the disease develops) is poorly understood 91,92

Severe cases of human metapneumovirus (HMPV) outbreaks causing illness and deaths among great apes in zoos have been repor ted In 2013, an HMPV infection that spread from humans to chimpanzees and back to humans was repor ted at a zoo in Slovenia 93 Four members of a group of six chimpanzees at the zoo developed bronchopneumonia, two of whom died. Their keeper also became ill with the same virus. In June 2024, a group of bonobos at Cincinnati Zoo, USA, contracted HMPV. The zoo stated that the virus may have originated in food thrown into the apes’ enclosure by visitors. The virus caused flu-like symptoms in the bonobos.94 In 2023, a young bonobo at the zoo had died from RSV, a virus in the same family.95 Bonobos are par ticularly susceptible to human RSV The zoo made no statement regarding the source of the outbreak

Tuberculosis, caused by the bacterium Mycobacterium tuberculosis, another zoonotic disease, can also be transmitted between humans and apes, resulting in respiratory distress and potential fatalities 96

During the Covid-19 pandemic, instances of SARS-CoV-2 infections among great apes in European zoos were documented, highlighting the susceptibility of these species to the virus In November 2021, an outbreak at Blijdorp Zoo in Rotterdam, the Netherlands involved seven western lowland gorillas and four Asiatic lions Investigations suggested that zookeepers were the probable source of the infections, although the precise transmission routes remained undetermined This incident underscored the potential for interspecies transmission within zoological settings 97 Additional cases were identified in gorillas in zoos in Spain and the United States.98

An outbreak of SARS-CoV-2 at Blijdorp Zoo infected seven western lowland gorillas

However, it is not just zoo staff who may pose a risk to great apes in captivity, and vice versa, but also visitors who attend zoos, including volunteers, contractors, media, and the general public. In 2009, a respiratory disease, which was likely to have been transmitted from zoo visitors to a group of chimpanzees at Chester Zoo, UK, resulted in the death of three of the apes 99 Measles caused by Morbillivirus hominis, can also be fatal in great apes 100

Gastrointestinal conditions, such as colitis and gastritis, are also prevalent in captive great apes These conditions can be caused by bacterial infections such as Escherichia coli and Salmonella, parasites such as Giardia and Entamoeba histolytica, or diet-related issues 101

Gorillas are par ticularly susceptible to gastro-intestinal diseases which are exacerbated by stress and can often result in death According to EAZA, chronic inflammation of the large intestines, including diseases mimicking human ulcerative colitis and Crohn’s disease, are very common in gorillas and can lead to bleeding into the gut and severe anaemia, perforation, and gut “leakage” into the abdominal cavity Peritonitis and death can result 10 Despite its relatively common occurrence, this issue remains poorly understood

Helicobacter infections have been linked to chronic gastritis in captive gorillas and chimpanzees, similar to their role in human ulcers.102

In the nor thern hemisphere, chimps and gorillas kept in zoos are par ticularly susceptible to the dog tapeworm Echinococcus multilocularis 100 During times of stress in the host, Balantidium coli parasites, which are commonly found in pigs and other farm animals, have been found to multiply in captive gorillas causing bowel inflammation which can result in dysentery and death 103 In August 2024, a gorilla at Jacksonville Zoo, USA, contracted and died from Shigella, a bacterial gastrointestinal infection typically spread through infected faeces Her death was swiftly followed by the death of two bonobos at the zoo While apes can be asymptomatic carriers of Shigella, the zoo admitted that the infection may have originated in zoo staff 104

Current EAZA best practice guidelines highlight the need for staff working with animals to be in good health, but also that zoos should under take pre-employment and subsequent, regular screening of staff to reduce the possibility of disease transmission to primates in their care EAZA guidelines also emphasise that “Under no circumstances should children be allowed to have direct contact with juvenile apes.”10

CO N F L I C T

When fights break out between great apes or when individuals are attacked in zoos, the inability to escape contributes to injuries or even deaths In 2024, a chimpanzee at Edinburgh Zoo died because of injuries sustained in a fight 105 31-year-old Rene was killed despite attempts by staff to intervene A second chimp required surgery for his injuries but made a full recovery The chimp exhibit at Edinburgh Zoo, which opened in 2008, has an enclosure measuring approximately 1,500m2 which is over 1,300 times smaller than the smallest recorded chimpanzee home range in the wild

In January 2025, a 50-year-old male chimpanzee named Dingo died at Safari Park Dvůr Králové in Czechia 106 He was found dead in his enclosure by keepers in the morning A veterinary autopsy revealed that the cause of death was serious internal organ injury, probably due to a fall or a fight Keepers believed that the incident was triggered by the chimpanzees being star tled and frightened by the noise of New Year fireworks.107

In 2022, a 47-year-old male chimpanzee named Rober t died at Leipzig Zoo in Germany, after his son usurped him as alpha male.108 With nowhere to escape, the other chimpanzees chased Rober t to the edge of his enclosure, where he fell into the surrounding moat and drowned Moats are often utilised in zoos to keep chimpanzees, who can’t swim, in their enclosures However, this can come at a fatal cost to captive animals should they enter the water

In 2011, Tiny, the first gorilla to be born at London Zoo for 22 years, suffered a broken arm and later died of internal injuries at just seven months of age, after he and his mother were attacked when they were introduced to a new male silverback, Kesho A leading evolutionary anthropologist and advisor to the International Union for Conservation of Nature (IUCN) on great apes, Professor Volker Sommer, accused the zoo of being “incompetent” and stated the zoo should not keep apes anymore 109 Current zoo industry guidelines recognise the risk of infanticide when introducing a silverback to a new group where juveniles are present and stipulate that such introductions should not occur if infants are less than four years old 10

C AS E S T U DY: AU S T I N A N D B O SS O U

At Dublin Zoo in 2013, t wo male chimpanzees, Aus tin and his son Bossou, were cas trated and under went dental procedures to remove t heir canines af ter t hey were identified as hybrids who could no longer par ticipate in t he captive breeding programme for chimpanzees.

Leaked veterinary records suggest that the dental surgery initially carried out on Austin was inappropriate as the surgeons were provided with an incorrect age at the time of procedure 110

In 2014, a former laboratory chimp, Marlon, was introduced to the same group despite lacking “ cer tain social skills” 111 Austin retained dominance over the group until a female named Florin died in 2020, at which point Marlon assumed dominance over the group. Two months later, Bossou is repor ted to have suffered significant injuries to his fingers as a result of an altercation with Marlon Dublin Zoo only under took the first surgical amputation of his damaged digits two months later Over a period of seven months, Bossou underwent four surgeries and had six digits amputated following repeated aggressive altercations

A 2022 investigation into the zoo revealed a zoo keeper testimony stating, “It was felt that Marlon would either kill Bossou or leave him in a state that required euthanasia This ultimately led to the decision to split the troop as they currently are

now During the last six months or so we effectively managed two troops living in the same house which improved Bossou’s welfare considerably but in turn created welfare issues for the rest of the troop ”

With their enclosure ill-equipped to provide for fission-fusion dynamics, or to allow Austin and Bossou to disperse as they would in the wild, Austin and Bossou along with an elderly female, Betty, were relocated to the zoo’s old gorilla house in February 2022. Betty died in July 2024 aged 62.112

In May 2025, the zoo publicly acknowledged that Bossou was overweight and both individuals were inactive when announcing the zoo was introducing additional items into their enclosure to encourage “exercise and locomotory behaviour” 113 At the time of writing, the welfare of Austin and Bossou remains unclear, with their access to the outdoors believed to be severely limited, despite continued pressure by campaigners

C AS E S T U DY: L I N DA , S A N T I N O , M A N DA ,

R S T E N , A N D S E L M A

In December 2022, four chimpanzees were shot dead at Furuvik Zoo, Sweden, after escaping from their enclosure through a door that was accidentally left open, following a combination of poor routines and human error.116 Female chimp Linda, 42, born in the wild in Liberia, and her three-year-old adopted son Torsten, who she was carrying, were shot and killed in the park’s snow covered fairground 23 Male chimp Santino, 44, and female Manda, 19, were shot inside the chimpanzee house Santino was repor tedly killed

C AS E S T U DY: B A ZO O

In June 2022, a 27-year-old chimpanzee named Bazoo was shot dead after he escaped from his enclosure at Attica Park Zoo in Greece. Bazoo had lived at Attica for 15 years and was the alpha male of the zoo’s nine chimpanzees.118 The zoo repor ted that staff had discovered Bazoo’s escape at 9:40am, following a repor ted incident or altercation between the chimpanzee group that resulted in him climbing over an electrified fence and the ditch around the enclosure, and

quickly but Manda was mor tally wounded Both chimpanzees were climbing in and out of the building through the window and it could not be guaranteed that they would stay inside the enclosure. Selma, 14, was shot and severely injured outside the chimpanzee house, suffering blindness in one eye, shrapnel in her body, and a fractured arm.117 The other two surviving chimpanzees were Torsten’s biological parents, Maria Magdalena, 22, and Tjobbe, 19, who remained inside the building

exiting the zoo to the car park The police were informed, visitors isolated and the security staff located Bazoo at the perimeter of the zoo where he was shot.119 People questioned why the animal was killed rather than tranquilised, but the zoo stated that the extremely high levels of adrenaline in Bazoo’s system meant that sedation was not possible, as it could take around twenty minutes for the drugs to take effect 120

C AS E S T U DY: M I K E A N D K A R I B U N A

In November 2020, two male chimpanzees were shot and killed after they escaped from their enclosure at Dierenpark Amersfoor t, the Netherlands 121 At around 10 30am officials evacuated the zoo after several chimpanzees got out of their enclosure, following the apparent failure by a keeper to shut or lock the enclosure

door properly 122 Some were repor tedly lured back with food but Mike, 55, and alpha chimp Karibuna, 20, were keen to explore fur ther afield 123 The zoo stated that the decision to shoot them was taken because the chimps were demonstrating dominant behaviour, which could have led to a dangerous situation.122

There have been at least 11 repor ted incidents of great ape escapes at European zoos since 2015

E S C A P E S

When great apes escape from their enclosures, the health and safety of those working within and visiting the zoo are put at risk, and it can also prove fatal for the animals involved Within the UK, under Appendix 12 of the Secretary of State’s Standards of Modern Zoo Practice, all great ape species are categorised as “Category ‘1’ (greater risk)” 114 This hazardous animal categorisation means that any contact between the public and such animals is “likely to cause serious injury or be a serious threat to life” For several Category ‘1’ species, zoos often adopt a ‘shoot-to-kill’ approach if they escape from their enclosure due to the inherent dangers the species can pose to zoo staff and the wider public Within Appendix B of the Standards of Modern Zoo Practice for Great Britain, which come into force in May 2027, great apes are categorised as “Category 1A (highest risk)”, a new category, which means “Contact between the public and any individual animals in Category 1A is highly likely to cause severe injury or be a serious threat to life”.115

Since 2015, there have been at least 11 repor ted incidents in European zoos where great apes have escaped from their enclosures. Six have involved chimpanzees; three have involved gorillas; and one involved an orangutan This is likely to be a considerable underestimate since escapes that do not end in tragedy may go unrepor ted

H U M A N H E A LT H A N D S A F E T Y

The risks of disease spreading from humans to apes, and vice versa (zoonoses) are detailed above Great apes also pose a serious safety risk when they are kept in unnaturally close proximity to humans in zoos Despite closing its doors in September 2022, the former Bristol Zoo site in the UK has continued to house western lowland gorillas while work on their enclosure at the new Bristol Zoo Project awaits completion. Since the old site’s closure, there have been a series of public break-ins, putting the health and safety of both the intruders and the gorillas at risk. The repeated disturbances and loud alarms have repor tedly had “really distressing” impacts in the gorillas.124 Fur ther afield, the tragic incident of a child falling into Harambe’s enclosure at Cincinnati Zoo, USA, in 2016 (see below) made international news; sadly, it is far from an isolated incident

C AS E S T U DY: H A R A M B E

Perhaps the most infamous great ape death in captivity is that of Harambe, a male gorilla shot dead at Cincinnati Zoo, USA, in 2016 A three-yearold boy fell into Harambe’s enclosure after crawling under fencing Zoo staff were able to call two of the three gorillas in the exhibit into an indoor space, but Harambe would not move inside Instead, he dragged the little boy around the enclosure’s moat, guarded him, and moved, pulled and pushed him around The terrified, screaming crowd of onlookers appeared to exacerbate Harambe’s behaviour. Ultimately, fearing that a tranquilliser dar t would take too long to take effect, zoo staff shot Harambe in the head, killing him. The little boy was rescued from the enclosure; he suffered serious but not life-threatening, injuries 125

C AS E S T U DY: M A L A B O

In 2020, 29-year-old male gorilla, Malabo, attacked a female zookeeper at Madrid Zoo, Spain She was repor tedly carrying out daily duties in an area of the enclosure that was supposed to be protected by a ‘triple door system’ but managed to come face to face with Malabo who then attacked her.

C AS E S T U DY: B A KO

In 2006, a female zookeeper, Lena Engström, at Borås Zoo, Sweden was attacked by an escaped orangutan. Bako, a 19-year-old male orangutan had managed to get out of his enclosure through a food hatch.128 Bako repor tedly came face to face with Lena as he roamed around.129 After managing to radio for help, her colleagues found 100kg Bako

C AS E S T U DY: B O K I T O

In 2007, 11-year-old male gorilla Bokito escaped his enclosure and ran amok through crowds of visitors at Blijdorp Zoo in Rotterdam, the Netherlands, injuring several people Bokito had repor tedly climbed over a high wall and across the water-filled moat to escape his enclosure.130 Four people were repor tedly injured in the panic. He grabbed one woman and dragged her to the

Repor ts stated that the boy was able to crawl under the inadequate zoo fencing, then fell into the moat of the gorilla’s enclosure 126

Harambe’s death sparked a global conversation, with many people outraged that the endangered gorilla was killed following the zoo’s failure to provide a safe environment for visitors The family of the little boy were also repor ted to have “ gone into hiding” due to backlash and accusations of child endangerment. Ultimately, Harambe’s tragic death sparked questions over whether or not gorillas should be in captivity at all.

The incident resulted in the keeper suffering serious injuries, including open fractures to both arms, chest trauma, and a head injury Staff managed to move Malabo away and he was anesthetised with a tranquilliser dar t and taken to his interior enclosure.127

sitting on top of Lena He had bitten her fingers and toes resulting in serious injuries and leaving Lena bleeding profusely.128 Bako only released his grip after workers hosed him with cold water, and he returned to his enclosure without a fight.129

ground, biting her and breaking her arm 131 Bokito was eventually barricaded inside the zoo’s restaurant, where he was sedated with a tranquilliser dar t In 2004, Bokito had previously escaped from his enclosure when he was at Berlin Zoo, Germany.130

Malabo attacked and seriously injured a zookeeper at Madrid Zoo

Harambe was shot dead at Cincinnati Zoo

Bokito escaped his enclosure at Bliijdorp Zoo, injuring several people

Bako escaped his enclosure at Borås Zoo and attacked a zookeeper

P R I M AT

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N A N D T H E RO L E ( O R O T H E RW I S E ) O F ZO O S

All great apes in regionally accredited zoos are managed as par t of global breeding programmes Many more are also likely being kept in non-accredited zoos Breeding programmes are ostensibly established by the zoo industry for the betterment of the species However, they are often operated without due consideration of what is best for the individual animals involved

The stated aim of breeding programmes is to achieve “population goals” by “managing a healthy, genetically diverse, and demographically varied population” in captivity 132 This somewhat vague mission does not explain how population goals are set and establishes the maintenance of captive populations as an end in itself, with little consideration of how this might contribute to species survival in natural habitats. This is par ticularly impor tant to note given that animals bred in captivity are rarely released into the wild.

Despite the lack of clarity around the purpose of EEPs, zoos make strong claims that breeding in captivity serves an impor tant conservation purpose and is endorsed by the IUCN However, it is disingenuous to suggest the IUCN endorses captive breeding programmes for the conservation of all species, especially given its Primate Specialist Group’s stance on the ex situ management of great apes (see below) 133 It is impor tant to note that captive breeding is not included in the IUCN’s recommended conservation actions for any species of great or lesser ape

In 2024, the IUCN Primate Specialist Group issued a statement expressly opposing the translocation of great apes from ex situ zoo breeding programmes outside of the species’ range States The statement says: “translocating great apes from ex situ zoo populations into wild great ape habitats poses risks with potentially serious negative consequences to wild great apes (conspecifics and other great ape species) that exceed potential conservation benefits” 134 The statement poses serious questions about the purpose of the continued captive breeding of great apes. We were unable to find any response from members of the zoo industry to the statement.

Since the IUCN Primate Specialist Group’s statement was released, zoos have continued to claim that great ape breeding programmes benefit conservation, including Colchester Zoo, UK, following the arrival of Napolean, a male chimpanzee, from Bioparc Fuengirola, Spain 135

It is notable that during a 2024 population management workshop for orangutans, more non-conservation related roles were suggested for ex situ zoo populations than direct conservation roles.8 Current EAZA Best Practice Guidelines for orangutans list a number of actions zoos can take including raising awareness of orangutans in the wild, the damaging impacts of unsustainable palm oil production, and the need for funding for field conservation work 36 All of these actions could be achieved without keeping and breeding orangutans in European zoos

In contrast to species and subspecies of great apes kept in zoos, the mountain gorilla (Gorilla beringei beringei ) is, at the time of writing, the only great ape subspecies which is increasing in number in the wild This is despite no individuals of this subspecies being currently kept in zoos 136

While the breeding and release of captive-born great apes to the wild from zoos is incredibly rare, there are a tiny number of examples where this has been achieved Since 1999, the Aspinall Foundation has continued with its stated rewilding mission and has returned 26 captive-born western lowland gorillas to areas of the Congo and Gabon on five separate occasions 137 Such an approach appears to be at odds with the IUCN’s recommendations, and it is unclear how this will impact any future releases.

H Y B R I D I S AT I O N O F A P E S I N ZO O S

The taxonomy of species is in constant flux as scientific data on genetics has grown and improved Animals once deemed to belong to a single species may be reclassified over time, often being split into either subspecies or into entirely separate species For example, bonobos were initially classified, in 1929, as a subspecies of chimpanzee but were later elevated to species status in 1933 More recently, in 2001, gorillas were reclassified from one species to two, each with two subspecies Orangutans were reclassified from one species with two subspecies, to two distinct species (Bornean and Sumatran) In 2017, a third species – the Tapanuli orangutan – was identified The Bornean orangutan has been fur ther split into three distinct subspecies

In light of the foregoing, hybridisation in zoos is inevitable as zoos have allowed animals belonging to what they believed to be the same species (or subspecies) to breed over time. Information regarding hybridisation is not often publicised but the 2015 Nor th American orangutan studbook provides some data on this subject. It suggests that, of the historic orangutan population in Nor th America, 28% (n=266) are either hybrids or their species is unknown. Similarly, recent DNA analysis of chimpanzees within the EEP identified that at least 46 individuals were hybrids 138 Overall, there were individuals belonging to each of the four recognised subspecies of chimpanzee within the EEP, despite the EEP being only intended for the western chimpanzee (P t verus) and the central chimpanzee (P t troglodytes) thus raising questions over the programme’s suitability to act as an effective insurance population for any of the currently recognised subspecies

While animals in zoos do not get released to the wild except in extremely rare cases, zoos argue that breeding animals allows them to maintain “insurance populations” in the event of the extinction or critical decline of species in the wild 139 The implication – if not the practice – is that animals from these insurance populations could be released to repopulate or reinforce existing wild populations in their natural habitats. This future potential is significantly compromised when hybridisation occurs in captivity The potential risks to existing populations when the ’wrong’ species or subspecies is released into a home range that is not their own, is difficult to quantify as there are limited data available, but there are concerns among exper ts that the resulting “genetic translocation” may harm the viability of already threatened species 140

Risks posed by the hybridisation of great apes, along with the emphatic statement released by the IUCN SSC Primate Specialist Group Section on Great Apes that breeding in zoos is not a valid conservation action for great apes, begs the question: how can the continued breeding of great apes in captivity be justified?

IUCN Primate Specialist Group stated that breeding great apes in zoos is not a valid conservation action

L E G I S L AT I O N

S U M M A RY

• Only just over half (27/50) of European sovereign States are members of the European Union and are therefore obligated to meet the requirements of the EU Zoos Directive.

• Within the UK, zoos must provide an environment well adapted to meet the physical, psychological and social needs of great apes.

• New British zoo standards entering into force in May 2027 contain a specific appendix related to great apes

• If implemented stringently and effectively, it is questionable whether any British zoo will be able to meet the revised standards for great apes in their entirety

Legislation regulating the keeping and management of great apes in zoos across Europe varies considerably between countries However, regardless of an individual animal’s location, the legislation which covers their welfare and management is typically broad and non-specific, if it exists at all

E U ZO O S D I R E C T I V E

Zoos situated within European Union (EU) Member States must comply with Directive 1999/22/EC, also known as the EU Zoos Directive. Most notably, Ar ticle 3 states that amongst other measures, zoos must, “[Accommodate] their animals under conditions which aim to satisfy the biological and conservation requirements of the individual species, inter alia, by providing species specific enrichment of the enclosures; and maintaining a high standard of animal husbandry with a developed programme of preventive and curative veterinary care and nutrition” Additionally, Ar ticle 4 of the Directive states that, “Member States shall adopt measures for licensing and inspection of existing and new zoos in order to ensure that the requirements of Ar ticle 3 are met”

Only just over half (27/50) of European sovereign States are members of the European Union Those that aren’t are not obligated to meet the requirements of the EU Zoos Directive, and the majority of these States are believed to have at least one zoo While some of these States may have adopted national regulations relating to zoos, often ar ticulated within the nation’s animal welfare legislation, others simply require a zoo to obtain a licence with no mandatory welfare criteria, and some have no provisions whatsoever

Overall, within Europe, there are concerns regarding the specificity of regulations which outline minimum welfare standards, and the mechanisms to identify welfare issues and effectively correct them.

For fur ther assessment of European zoo legislation see Born Free’s publication: Clawing at the Cages: The problem with keeping big cats in zoos (https://www bornfree org uk/resource/clawing-at-the-cages/)

ZO O L I C E N S I N G AC T 1981

Within the UK, facilities other than pet shops that keep wild animals and are open to the public for seven or more days within a calendar year require a licence under the Zoo Licensing Act 1981 (as amended) The Act outlines broad conditions which a zoo must meet in order to obtain and retain its operating licence

Section 1A of the Zoo Licensing Act states that zoos must be:

“(c) accommodating their animals under conditions which aim to satisfy the biological and conservation requirements of the species to which they belong, including

(i) providing each animal with an environment well adapted to meet the physical, psychological and social needs of the species to which it belongs ”

The content of this repor t challenges whether any zoo in the UK can meet the physical, psychological, and social needs of great apes as required by section 1A (c) of the Zoo Licensing Act

Fur ther guidance on the standards which zoos should meet in order to fulfil their licensing conditions are provided within published standards (see below).

Standards of Modern Zoo Practice for Great Britain

In May 2025, The UK government’s Depar tment for Environment, Food and Rural Affairs (DEFRA) published revisions of the Secretary of State’s Standards of Modern Zoo Practice, renamed the Standards of Modern Zoo Practice for Great Britain, which will come into effect in May 2027 115

While, overall, the revised standards are disappointing and represent a missed oppor tunity for transformational change, encouragingly they contain a new section of species-specific requirements for great apes within Appendix A9 The Standards acknowledge that great apes are socially and cognitively complex Under these revised standards, British zoos will be required to develop long-term management plans (LTMP) for each great ape in their care which should cover the following 25 years and should be reviewed annually Additionally, zoos must review enclosures every five years to make sure they meet the welfare needs of great apes Zoos are also required to produce a Welfare Management Plan for each great ape species they keep.

In the revised standards, zoos are explicitly directed to keep chimpanzees, bonobos and orangutans in fission-fusion social groups. Zoos must also ensure great apes have continuous 24-hour access to outdoor, indoor and off-show areas of their enclosure, which are constructed in a manner which meets their terrestrial or arboreal lifestyle

However, the standards contain loopholes which provide oppor tunities for zoos to justify why their enclosures do not meet the requirements, rather than being obliged to improve the enclosures or accept that they are no longer legally compliant and phase out their great apes

Despite the requirement for zoos to provide 24-hour outdoor access, as highlighted in this repor t many great apes in Britain will likely spend the majority of their winter months indoors Following the consultation on the standards, Born Free raised the impor tance of additional UV lighting in indoor areas for great apes who may experience limited natural light, par ticularly in winter months This requirement was added to the finalised standards and is now contained within Section A9.17.

There are also concerns that for zoos breeding great apes who are not being maintained in stable, multigenerational groups, the final decision on whether this is appropriate seems to rest with the zoo’s own ethics committee rather than the inspectorate and local licensing authority whose responsibility it will be to enforce the revised standards (Section A9 3(c)) However, it is encouraging that the standards also state zoos that “cannot achieve stable, multi-generational groups in diverse and environmentally stimulating, expansive environments must proactively review and implement changes to their LTMP or divest themselves of their great apes ” The latter of the two options was put forward by Born Free during the consultation period

The revised standards also stipulate that zoos will be required to provide appropriate planting in the outdoor enclosures of great apes Due to the sometimes destructive nature of captive great apes, there are concerns that although natural planting may be included, great apes may be prevented from accessing the plants via the use of hot wires or other deterrents, rendering them largely cosmetic and having little beneficial impact on great ape welfare, and fur ther highlighting how zoos cannot provide a suitable environment for great apes.

Although concerns remain with respect to the language within the great ape appendix, its inclusion within the overall standards, and its reference to zoos potentially needing to divest of their great apes should they not meet the standards, is cautiously welcomed, and reflects the complex social, physical and cognitive needs of great apes If implemented stringently and effectively, it is questionable whether any British zoo will be able to meet these revised standards in their entirety

CO N C L U S I O N

In t his repor t, we have laid out compelling evidence to challenge t he continued keeping of great apes in zoos.

Suffering from poor health and welfare, unnatural social groupings, poor longevity, and other negative impacts, life in zoos for our closest cousins is bleak. Some may argue that the purpose of keeping apes captive is to protect their species from extinction. But as we have set out, captive great apes are hardly ever released into the wild, nor are such releases currently recommended by international conservation organisations In addition, hybridisation in zoos creates potential risks to wild populations even if release were possible Moreover, exper ts emphatically state that breeding apes in zoos is not a valid conservation action, yet breeding continues with zoos publicly claiming the impor tance of each captive bir th

Great apes in zoos pose risks to humans, and vice versa Even trained members of staff have been severely injured in attacks, either during escape incidents or when going about their normal daily routines, for example during feeding When humans are attacked by captive apes –often because of human error or infrastructure failure – the animals often pay with their lives. Harambe the gorilla’s death is the most infamous, but he is just one of the many great apes who have died in zoos following dangerous incidents arising from their confinement.

Similarities between humans and great apes make for increased risk of disease spread, placing apes in an unusually vulnerable position when it comes to the spread of zoonotic disease

Overall, the litany of concerns clearly evidenced in this repor t makes the phasing-out of great apes in zoos the kindest, safest, and most ethical solution Indeed, based on the evidence, this approach is also the most logical To continue to keep these complex beings in captivity for our enter tainment can no longer be justified on the basis of science, welfare, or animal and public safety

In the shor t term, we call on the UK Government to:

• Introduce an immediate moratorium on the breeding and impor tation of great apes into UK zoos

• Ensure the welfare of existing great apes in UK zoos is prioritised through the robust and thorough implementation of the Great Ape Appendix within the Standards of Modern Zoo Practice for Great Britain

• Work with zoos and other stakeholders to assist those zoos that cannot meet the new Standards to end their keeping of great apes whilst prioritising the welfare needs of the individual great apes concerned

In the long term, we call on national governments, regulators, national and regional zoo associations and NGOs to work together, humanely, compassionately, and respectfully, to phase out the keeping of great apes in zoological collections.

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F E R E N C E S

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