Seychelles warbler  (Acrocephalus sechellensis)

The reasons behind the Seychelles warblers past decline is a story that is echoed across many islands throughout the world. Following human colonisation, the natural habitat of the Seychelles was extensively modified, particularly between 1910 and 1920 when most of the islands were planted with coconut palms (Cocos nucifera). This left very little suitable natural habitat for the Seychelles warbler and as a result, and in combination with the effects of introduced predators, this species subsequently disappeared from all islands except for Cousin. Since that time, until around 1968, the global population of Seychelles warblers was restricted to just a one hectare patch of mangroves and numbered around only 26 individuals (3) (5). Thankfully, 1968 saw Cousin being purchased and managed as a nature reserve, and the regeneration of native vegetation allowed the warbler population to recover (3) (5). Subsequent human intervention also established new populations on Aride, Cousine and Denis (3).

Whilst this is a remarkable story of how the warbler's extinction was successfully averted, a number of threats remain to this vulnerable bird. Cousin Island has so far remained free of introduced predator species, such as cats and rats, and introduced competitors, but the accidental or intentional introduction of any of these species to Cousin undoubtedly poses a great threat to the future of the warbler (5). While Cousin Island is now a nature reserve, and thus the protection of its habitat remains secure, Cousine Island is privately owned and hence the future of the island remains uncertain (3). The decline of the warbler to such a tiny number in the past probably left the population with severely limited genetic variation and the negative effects of inbreeding poses a potential long-term threat (3). In addition, if predictions of global warming and sea level rise are correct, this may result in the loss significant areas of the warbler's habitat, which is found at sea-level (3).

The turning point for the Seychelles warbler, when it was on the brink of extinction, came with the purchase of Cousin Island in 1968 and its management as a nature reserve (3). Intense efforts to clear coconut trees allowed native vegetation to regenerate and by 1982 most of the island was covered with tropical, primarily native, forest (5). By this point, Cousin Island supported the largest Seychelles warbler population that was possible, and so new populations were established on Aride and Cousine Island (3), and later to Denis Island (4). Both Cousin and Aride are protected as Nature Reserves under Seychelles Law and management of the habitat continues, with efforts also aimed at keeping the islands rat-free (3). The establishment of five separate populations on five islands has been deemed necessary to improve the conservation status of this species and with four breeding populations already established (3) (4), it may not be long before this goal is achieved.