The Seychelles Warbler (Acrocephalus sechellensis), also known as Seychelles Brush-warbler, is a small songbird found on four granitic and corraline islands in the Seychelles. It is a greenish-brown bird with long legs and a long slender bill. It is primarily found in forested areas on the islands. The Seychelles Warbler is a rarity in that it exhibits cooperative breeding, or alloparenting; which means that the monogamous pair is assisted by nonbreeding female helpers.
A few decades ago the Seychelles Warbler was on the verge of extinction, with only 50 birds surviving on Cousin Island in 1965. Due to conservation efforts there are more than 2500 of the species alive today with viable populations on Denis, Cousine and Aride Islands, as well as Cousin Island.
The Seychelles Warbler is a small, plain Acrocephalus warbler, between 13-14 cm in length and with a wingspan of 17 cm. It has long grey-blue legs, a long horn coloured bill, and a reddish eye. Adults show no sexual dimorphism in their plumage, the back, wings, flanks and head are greenish brown and the belly and breast are dirty white. The throat is a stronger white and there is a pale supercilium in front of the eye. Juvenile birds are darker with a more bluish eye.
The voice of the Seychelles Warbler is described as rich and melodious, similar to a human whistle. Its structure is simple and is composed of short song sequences delivered at a low frequency range. The lack of a wide frequency range sets it apart from other species in its genus, such as the Reed Warbler, its song is similar to its closest relatives in Africa such as the Greater Swamp Warbler. Some authors put the species, along with the Rodrigues Warbler, in the genus Bebrornis, although Bebrornis it is more usually considered a subclade or subgenus of Acrocephalus, and is not at any rate supported by molecular analysis.
The Seychelles Warbler naturally occur in dense shrubland and in tall forests of Pisonia grandis. It is almost exclusively an insectivore (99.8% of its diet is insects), and obtains 98% of its prey by gleaning small insects from the undersides of leaves. It does occasionally catch insects on the wing as well. Most of the foraging occus on Pisonia, Ficus luea[verification needed] and Morinda citrifolia. Studies of the foraging behaviour found that Seychelles Warblers favour Morinda and spend more time foraging there than in other trees and shrubs, the same study found that insect abundance is highest under the leaves of that shrub. The planting of Morinda on Cousin, and the associated improved foraging for the warbler, was an important part of the recovery of the species.