Seychelles warbler  (Acrocephalus sechellensis)

The Seychelles warbler stands as an example of how, whilst humans may push a species to the verge of extinction, human intervention may also protect a species from this fate. Once believed to have just 26 individuals remaining on this planet, the Seychelles warbler, with its long, rather stout bill and long tail, is now thriving (2) (3). Its plumage is dull, yellowish olive-brown with a greenish wash, which fades to pale, faintly streaked, yellow on the underparts. The wing feathers are darker and browner and the tail feathers are also darker but with white tips (2). A whitish line runs above the eye, while an indistinct stripe extends from the bill to the reddish-brown eye and continues behind it. The Seychelles warbler's legs are grey-blue. Males and females are similar in appearance, while juveniles have grey-brown or grey-blue eyes (2). Seychelles warblers sing a short but rich and melodious song of simple whistled phrases, and they call in alarm with a brisk chatter (2).

The Seychelles warbler currently occurs on the islands of Cousin, Cousine, Aride and Denis in the Seychelles (2) (3) (4). Historically, this species is believed to have also existed on Marianne, possibly Praslin, and there were also occasional reports from Mahé and Félicité (3).

Thick scrub and dense, tall woodland dominated by the tree Pisonia grandis are the Seychelles warbler's preferred habitats (3), but it also occurs in scrub in old coconut plantations, and swamps and mangroves (2).

The Seychelles warbler feeds primarily on a variety of insects, including bugs and their eggs, beetles, bees and ants. It also feeds on spiders and, occasionally, small skins and geckos (2). It forages for its prey in trees, particularly Pisonia grandis, Morinda citrifolia (the Indian mulberry) and Ficus (fig) species, plucking insects from the undersides of leaves and twigs (2) (3) (5). Occasionally, aerial insects are plucked from the air whilst in flight and rarely the warbler will descend to the ground to feed (2) (3).

Being a monogamous bird, male and female Seychelles warblers form pairs and together defend a territory which they will remain in until one of the pair dies (2) (3). The peak breeding period occurs between June and August, with a smaller peak of breeding attempts occurring between December and February. The timing of breeding throughout the year seems to be dependent on rainfall, however, breeding may occur at any time of the year if insects are sufficiently abundant (3).

Seychelles warblers have a cooperative breeding system, meaning that helpers, usually the daughters from previous broods, assist with defending the territory, building the nest, incubating the eggs and feeding the young (6). Normally, a clutch of just one egg is laid each season, which is incubated for around 15 days, and the chick remains in the nest for a further 14 days (3). However, even after leaving the nest the young warbler will continue to solicit food from its parents and helpers for months afterwards (3).

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.

For further information on the Seychelles warbler and other Seychelles species see:

• Nature Protection Trust of Seychelles:
  http://members.aol.com/jstgerlach

• Nature Seychelles:
  www.natureseychelles.org

This information is awaiting authentication by a species expert, and will be updated as soon as possible. If you are able to help please contact:
arkive@wildscreen.org.uk