GETTING MARSUPIAL HUSBANDRY OFF THE GROUND

The care and keeping of the little-known ground cuscus.

The ground cuscus (Phalanger gymnotis) is a species of marsupial endemic to New Guinea and the Aru Islands. Although thought to be common across its range, little is known about this cryptic animal. Recent studies suggest population numbers are decreasing and already, it has been extirpated from parts of its former distribution because of excessive hunting. As a species which is rarely exhibited in zoos and is only maintained in a handful of collections, there is a significant gap in our knowledge of ‘best practice’ husbandry guidelines for the ground cuscus. This has prompted staff and students at Hadlow College to lead the charge in developing our understanding of these unique animals.

Getting things off the ground

There are 13 species belonging to the Phalanger genus, which are colloquially named: cuscuses. These nocturnal marsupials can be found from the Cape York Peninsula in North Queensland to Papua New Guinea and the neighbouring islands. They are closely related to possums and live primarily arboreal lives in a diverse range of habitats from tropical forests to urban areas. The ground cuscus is found in the northern half of Papua New Guinea and the neighbouring islands and despite being first kept in the early 20th Century, has been studied by reasonably few institutions. Although the species is currently categorised as "least concern" by the IUCN, there is reason to believe that population numbers are declining at an alarming rate.

Paige Conneely, BSc Student and Animal Management Assistant at Hadlow College told Exotics Keeper Magazine: “The ground cuscus has a history of being collected for the illegal pet trade and hunted for traditional medicines. Their body parts are thought to preserve the health of local people, making them more of a commodity in their home ranges. Because of this, unfortunately, it is more socially acceptable for them to be hunted and collected illegally from the wild.”

“The first record of these guys in captivity dates to 1933, so they have been kept for a while. In the UK there are around 13 collections housing them, but they are typically off-show and mostly in colleges. The UK has the most collections housing them on record, with just a few more dotted around Europe and the US. Currently, there is no studbook for this species, so it’s really important that we network with other collections on husbandry practices. EAZA has shown interest in their decline back in 2019 and again in 2020, so we’re waiting on this year’s report to see what further comments have been made for this species.”

The college began keeping ground cuscuses in 2016 and since then has invested a lot of time into understanding their husbandry needs and cognitive abilities. Now, the college keeps a pair; ‘Bulolo’ and ‘Morobe’. These animals are helping to inform other institutions on dietary requirements and enrichment strategies that could be applied to a range of taxa.

Enclosure design

Creating an appropriate enclosure for a rarely studied mammal can be a challenge. The college has created both an indoor climate-controlled area, as well as an outdoor exhibit for the cuscuses to utilise. The animals always have access to both parts of the enclosure (unless the hatch needs to be closed to maintain indoor temperatures).

“Although they are called the ‘ground’ cuscus, we’ve noticed that they will spend most of their time in elevated positions” explains students, Mia and Paige. “They are from a wide variety of habitats and in the wild, they will use hollowed-out trees and cave systems as shelter, so it isn’t surprising that they prefer their higher nest boxes.”

“Although they look slow, they can move extremely quick. They can lunge and jump quite easily. In our experience, they have a mixture of arboreal and terrestrial behaviours. They each have a favourite spot and very distinct personalities. We do find that in summer when the sun sets a bit later, they will come out a bit later. They have that slight change based on the natural cycle. When it’s a bit colder, they will also come out a little earlier. We’re lucky to be able to give them this natural fluctuation that they wouldn’t have in a red light, nocturnal zoo exhibit.”

To cater for the species’ mixed behaviours, BSc students Mia and Paige have utilised a range of climbing and burrowing opportunities by experimenting with different substrates, burrows, climbing apparatus and nest boxes. The students have also chosen to build most of the climbing apparatus out of modular items that can be

Indoor enclosure at Hadlow College

easily changed and replaced. Daniel Sutherland, Animal Management Unit Manager added: “Originally, they were on soil with a bit of bark. Over the years this has washed away. So, we experimented with different textures. At the minute we have some beech chips and some soil. We also have a stony area in the flower bed and there is a huge flowerpot in the exhibit that we maintain with loose soil so that they can dig into it if they want to. We sometimes hide some of their food in there too. In the wild, they are frequently found by rivers and streams and they will tend to burrow closer to bodies of water. We are in the process of upgrading the enclosure and will aim to give them a much larger water area, even though it’s not something you would typically associate with an arboreal mammal”.

Mia Birchall, BSc Animal Management Student at Hadlow College added: “I don’t think that working with a nocturnal species is a challenge. Obviously, we can’t be so hands-on with them, but we can record their behaviour using camera traps and they do still come out during the day. We still maintain the species and work on their husbandry even though we don’t have them set up in a ‘nocturnal’ exhibit. We have learnt a lot about the breeding side of things. For example, they will pull fur out, and exhibit ‘scent marking’ behaviours by secreting scents from their glands and urinating. There are also obvious faecal changes when they start to exhibit breeding behaviours. A lot of this has come from observations on the camera traps.”

Enrichment strategies

Enrichment is extremely important for all animals, but creative methods of cognitive enrichment are essential for most exotic mammals. Perhaps this is because we understand more about the mammalian brain, or because animals such as the ground cuscus have digits which they can use to solve puzzles. Either way, testing the boundaries of a species’ cognitive ability is crucial in understanding more about its natural history and behaviours. “We’re currently looking into unpredictive feeding as enrichment” Paige explained. “Sort of how you might have a cat feeder on a timer, we are going to fix one of these to the wall as a feeding method. That is the main challenge we face with nocturnal species - because we don’t see them during the night, we have to put all their food out in the morning and wait for them to come and get it.”

“We’re also testing their cognitive abilities with other enrichment techniques” added Mia. “We place their food onto wooden skewers and fix them into the ground or some mesh. We’ve also smeared honey onto pinecones which Bulolo really loves! We’ve smeared pellets into holes and logs. We’ve used paper bags and hay-filled boxes to hide foods. Sometimes we’ll cut up egg boxes, so they have to put their hands in to get the food. We have also created ball pits for them to forage through. Other places have used scent trails too.”

The staff and students have made several interesting observations through their enrichment strategies already. Mia continued: “Anecdotally, we’ve found that when they have to work for their food, they will eat much more of it. We’ve been stretching their cognitive abilities and I think that’s even more important for a nocturnal species. They come out at night and actually have to work for their food. They are very handsy. When they pick up a food item, they do manipulate it. They will peel bananas and take the skin off of any fruit that we give them.”

Dietary elements and ‘treats’ play a major role in cognitive enrichment techniques across most taxa. Generally, most insectivores or carnivores must hunt what they can to survive. Prey is scarce and therefore most feeds will have consistently suitable nutritional profiles. Omnivorous, herbivorous and frugivorous animals can afford to be slightly fussier. In the wild, this is mitigated by seasonality. For example, many high-sugar fruits and nuts will only be available during certain times of the year. In captivity, many exotic mammals with broad diets are susceptible to obesity because of the high sugar content in commercially farmed food. This is even more true for frugivorous mammals, which can present a real challenge to keepers. “To ensure we can still provide a healthy diet; we also tweak the food presentation too” added Dan. “So, one day they might get a whole sweet potato, other days it’ll be boiled and mashed and placed in different areas, and sometimes it’ll be cut into different-sized chunks. This provides enrichment, without the need to feed high-sugar items. They will also manipulate vegetables in the same way they will manipulate fruit, which provides some added enrichment. They will use their teeth to peel the skins from carrots and cucumbers, even though these are items they wouldn’t have access to in the wild.”

Diet

The dietary requirements of frugivorous/herbivorous mammals are an interesting topic. On the surface, most will eat a very broad range of plants and will generally exhibit signs of ill health much sooner than stoic reptiles, giving the impression that they are ‘easy’ to feed. On the other hand, their true wild diets are much less wellknown and perhaps more difficult to facilitate in UK-based collections (particularly the range of tropical fruits with specific nutrient profiles). Therefore, keepers must find a middle ground that provides all the essential nutrients to their animals, whilst also simulating wild forage as closely as possible.

“Over 98% of the flora found across their range is endemic to the area, so it’s difficult to pinpoint exactly what types of vegetation they would be eating in the wild” explained Paige. “Papua New Guinea is one of the most biodiverse places in the world. Also, very few collections have kept historical records of what they’ve successfully fed them on. Their main diet here is rooty vegetables, things like sweet potato and leaves such as chard, kale, spinach, that sort of thing. We only use the fruit for training, to make sure we don’t overdo it with the sugar. We have tried various browse, so things like willow, lime, hawthorn. They have a bit of bamboo growing in their enclosure, but they rarely eat it. Again, that’s why it’s so important to reach out to new collections. If it’s a universally accepted plant we’ll feed it, but then try new things as well.”

“We have to be very careful with sugar content. For example, our bananas are a lot more sugary than the ones they would eat in the wild. They do really like grapes, strawberries, pears and apples. Obviously, they are frugivores but we can simulate that sweet taste of fruit with lower sugar alternatives, which would be more akin to the nutrients they would receive from wild fruits. These are things like roses and coconuts which are naturally sweet. So far, we haven’t seen a big difference in weight, so we’re confident in what we’re doing but still perfecting the formula. Unfortunately, there’s just not that information out there.”

Mia also added that both animals have distinct tastes. Bulolo is particularly fond of peanut’s whereas Morobe is