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Apapane and mosquito Š JACK JEFFREY Introduced mongoose, Jamaica Š LEO DOUGLAS Black-faced Spoonbill Š MARTIN HALE P. 45:

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Humans have been transporting animals from one part of the world to another for thousands of years, sometimes deliberately (e.g. livestock released by sailors onto islands as a source of food) and sometimes accidentally (e.g. rats escaping from boats). In most cases, such introductions are unsuccessful, but when they do become established as ‘alien invasive species’, the consequences 1

can be catastrophic. Invasives can affect native species by eating them, competing with them, hybridising with them, disrupting or destroying their habitat, or introducing pathogens or parasites that sicken or kill them. Over the last five hundred years, alien invasives have been partly or wholly responsible for the extinction of at least 65 bird species, making this the most common contributory factor in recent losses to the world’s avifauna (see box 1).

Invasive species have been implicated in nearly half of recent bird extinctions

In total, 129 bird species are classified as having gone extinct since 15001,2 (see pp. 12-13). The impacts of alien invasive species, over-exploitation by humans, and habitat destruction and degradation have been the major contributory factors (see figure)3. Invasive species are associated with the extinction of at least 65 species. Predation by introduced dogs, pigs and mongooses, and habitat destruction by sheep, rabbits and goats, have been implicated in some cases. However, it is predation by introduced rats and cats, and diseases The major threats contributing to bird extinctions since 15003 caused by introduced pathogens, that have been  the most deadly, contributing to the  extinction of some 30, 20  and 10 species respectively. SOURCES 1. Brooks (2000) Pp. 701– 708 in BirdLife International Threatened birds of the world. Barcelona and Cambridge, UK: Lynx Edicions and BirdLife International. 2. BirdLife International (2004) Threatened birds of the world 2004. CD-ROM. Cambridge, UK: BirdLife International. 3. Analysis of data held in BirdLife’s World Bird Database.

     Invasive OverHabitat Unknown species exploitation destruction/ degradation

Natural Persecution Changes disasters in native species

Invasive species are a particular threat on islands Currently, nearly 30% of Globally Threatened Birds (GTBs) are affected by alien invasive species, making this the third most important threat after habitat destruction and over-exploitation (see pp. 30–31). Island species are particularly susceptible because of their isolated evolutionary history, with 67% of oceanicisland GTBs affected by invasive 2

species (box 2). The arrival of new invasives in the near future is a very real threat for almost 50 island species. There is particular concern for bird species in Micronesia. The brown tree snake has already caused severe ecological, economic and health problems on Guam since it was accidentally introduced shortly after World War II (including the local and global extinction of several native bird, bat, and lizard species).

Small island species are most at risk from invasives

In total, 326 Globally Threatened Birds (GTBs, nearly 30% of the total) are currently threatened by alien invasive species1. The problem is especially acute on islands, particularly small ones (67% of GTBs on oceanic islands are threatened by invasives, see figure a)2, where long isolation has led to the (a) Sixty-seven percent of GTBs on oceanic islands are affected by invasive species, a much higher figure than on continental islands evolution of species that or continents2 often lack adequate defences against introduced Continental islands Continents Oceanic islands species. The majority of (190 GTBs) (620 GTBs) (432 GTBs) species (95%) are affected 8% 67% 17% by introduced predators, but many are subject to multiple impacts from a range of invasives (figure b)2. One such example is Galåpagos Petrel Pterodroma phaeopygia (Critically GTBs threatened by invasive species Endangered) which has GTBs not threatened by invasives undergone an extremely rapid decline since the early (b) Ninety-five percent of GTBs threatened by invasives are 1980s owing to a variety of affected by invasive predators2 threats, including predation  by introduced rats, cats and dogs, and the destruction  of breeding habitat by  introduced goats and  cattle1. SOURCES 1. BirdLife International (2004) Threatened birds of the world 2004. CD-ROM. Cambridge, UK: BirdLife International. 2. Analysis of data held in BirdLife’s World Bird Database.

Number of GTBs impacted

Invasive species of animals, plants and disease-causing microorganisms are a particular threat to birds on islands, and have already caused numerous extinctions. Global travel, trade and a changing climate are encouraging the spread of invasives world-wide, including damaging diseases.

Invasive species are the main cause of recent bird extinctions

Number of extinct species

Alien invasive species, including diseases, are spreading






  Pathogens/ parasites

Nature of alien invasive species


State of the world’s birds 2004  

State of the world’s birds provides information on how birds can be used to focus action and as indicators to monitor change. Using the most...

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