Seychelles warbler

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Seychelles warbler

Near Threatened  (IUCN 3.1)[1]
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Aves
Order: Passeriformes
Family: Acrocephalidae
Genus: Acrocephalus
Species:
A. sechellensis
Binomial name
Acrocephalus sechellensis
(Oustalet, 1877)
Synonyms

Bebrornis sechellensis[2]

The Seychelles warbler (Acrocephalus sechellensis), also known as Seychelles brush warbler,[2] is a small songbird found on five 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 26 birds surviving on Cousin Island in 1968. Due to conservation efforts there are more than 2500 of the species alive today with viable populations on Denis, Frégate, Cousine and Aride Islands, as well as Cousin Island.[3]

Taxonomy and systematics

The Seychelles warbler is closely related to the Rodrigues warbler (Acrocephalus rodericanus) and the two species have sometimes been placed in their own genus, Bebrornis. The two species have also been considered allied to the Malagasy genus Nesillas. A 1997 study confirmed, however, that the two species were part of a clade of Afrotropical warblers within Acrocephalus that also includes the Madagascar swamp warbler, the greater swamp warbler, the lesser swamp warbler and the Cape Verde warbler.[4][5][6]

Description

The Seychelles warbler is a small, plain Acrocephalus warbler, between 13 and 14 cm (5.1–5.5 in) in length and with a wingspan of 17 cm (6.7 in).[7] 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

reed warbler, its song is similar to its closest relatives in Africa such as the greater swamp warbler
.

Behaviour

The Seychelles warbler naturally occurs in dense

Morinda citrifolia.[10] 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.[11]
The planting of Morinda on Cousin Island, and the associated improved foraging for the warbler, was an important part of the recovery of the species.

Cooperative breeding habits

Seychelles warblers demonstrate cooperative breeding, a reproductive system in which adult male and female helpers assist the parents in providing care and feeding the young.[12] The helpers may also aid in territory defense, predator mobbing, nest building, and incubation (females only).[13] Breeding pairs with helpers have increased reproductive success and produced more offspring that survived per year than breeding pairs with the helpers removed.[14] Helpers only feed the young of their parents or close relatives and do not feed unrelated young. This is evidence for the kin-selected adaptation of providing food for the young. The indirect fitness benefits gained by helping close kin are greater than the direct fitness benefits gained as a breeder. This could be evidence for the kin-selected adaptation of providing food for the young.

On high-quality territories where there is more insect prey available, young birds were more likely to stay as helpers rather than moving to low-quality territories as breeders.[15] On low quality territories, having a helper is unfavorable because of increased resource competition. Females are more likely to become helpers,[16] which may explain the adaptive sex ratio bias seen in the Seychelles warblers. On high quality territories, females produce 90% daughters; on low quality territories, they produce 80% sons. Clutch sex ratio is skewed towards daughters overall.[17] When females are moved to higher quality territories, they produce two eggs in a clutch instead of a single egg, with both eggs skewed towards the production of females. This change suggests that Seychelles warblers may have pre-ovulation control of offspring sex ratio, although the exact mechanism is unknown.

References

  1. doi:10.2305/IUCN.UK.2016-3.RLTS.T22714882A94431883.en
    . Retrieved 12 November 2021.
  2. ^ a b Penny, M. (1974): The Birds of Seychelles and the Outlying Islands
  3. S2CID 4519848
    .
  4. S2CID 40665930
    .
  5. PMID 10191069
    .
  6. ISBN 978-84-96553-06-4
  7. ^
    ISBN 0-7136-3973-3
  8. doi:10.1111/j.1474-919X.1994.tb01127.x
    .
  9. ^ Richardson D. (2001) Species Conservation Assessment and Action Plan, Seychelles Warbler. Nature Seychelles.
  10. ^ "Seychelles Warbler Acrocephalus sechellensis". BirdLife International. Retrieved 24 August 2015.
  11. doi:10.1016/j.biocon.2004.12.009
    .
  12. S2CID 54796150
    .
  13. S2CID 54796150
    .
  14. S2CID 35183524
    .
  15. S2CID 4364419
    .
  16. ^ Davies, N. B., Krebs J. R., West, S. A. (2012). An Introduction to Behavioural Ecology. Fourth Edition. West Sussex, UK: Wiley-Blackwell.
  17. PMID 12028765
    .

External links

Wikimedia Commons has media related to Acrocephalus sechellensis.
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