TheSeychelles warbler(Acrocephalus sechellensis), also known asSeychelles brush warbler,[2]is a smallsongbirdfound on five granitic and corraline islands in theSeychelles.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, oralloparenting,which means that the monogamous pair is assisted by nonbreeding femalehelpers.
| Seychelles warbler | |
|---|---|
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Scientific classification
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| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Aves |
| Order: | Passeriformes |
| Family: | Acrocephalidae |
| Genus: | Acrocephalus |
| Species: | A. sechellensis
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| Binomial name | |
| Acrocephalus sechellensis (Oustalet,1877)
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| Synonyms | |
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Bebrornis sechellensis[2] | |
A few decades ago the Seychelles warbler was on the verge ofextinction,with only 26 birds surviving onCousin Islandin 1968. Due to conservation efforts there are more than 2500 of the species alive today with viable populations onDenis,Frégate,CousineandAride Islands,as well as Cousin Island.[3]
Taxonomy and systematics
editThe Seychelles warbler is closely related to theRodrigues 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 genusNesillas.A 1997 study confirmed, however, that the two species were part of a clade of Afrotropical warblers withinAcrocephalusthat also includes theMadagascar swamp warbler,thegreater swamp warbler,thelesser swamp warblerand theCape Verde warbler.[4][5][6]
Description
editThe Seychelles warbler is a small, plainAcrocephaluswarbler, 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-colouredbill,and a reddisheye.Adults show nosexual dimorphismin theirplumage.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.
Thevoiceof the Seychelles warbler is described asrich and melodious,[7]similar to a humanwhistle.Its structure is simple and is composed of short song sequences delivered at a low frequency range.[8]The lack of a wide frequency range sets it apart from other species in its genus, such as thereed warbler,its song is similar to its closest relatives in Africa such as thegreater swamp warbler.
Behaviour
editThe Seychelles warbler naturally occurs in denseshrublandand in tall forests ofPisonia grandis.It is almost exclusively aninsectivore(99.8% of its diet is insects), and obtains 98% of its prey bygleaningsmall insects from the undersides of leaves. It does occasionally catch insects on the wing as well.[9]Most of the foraging occurs onPisonia,Ficus reflexaandMorinda citrifolia.[10]Studies of the foraging behaviour found that Seychelles warblers favourMorindaand 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 ofMorindaon Cousin Island, and the associated improved foraging for the warbler, was an important part of the recovery of the species.
Cooperative breeding habits
editSeychelles warblers demonstratecooperative 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 thekin-selectedadaptation of providing food for the young. The indirectfitnessbenefits 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 adaptivesex ratiobias 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
edit- ^BirdLife International (2016)."Acrocephalus sechellensis".IUCN Red List of Threatened Species.2016:e.T22714882A94431883.doi:10.2305/IUCN.UK.2016-3.RLTS.T22714882A94431883.en.Retrieved12 November2021.
- ^abPenny, M.(1974):The Birds of Seychelles and the Outlying Islands
- ^Johnson, Thomas F.; Brown, Thomas J.; Richardson, David S.; Dugdale, Hannah L. (2018)."The importance of post-translocation monitoring of habitat use and population growth: Insights from a Seychelles Warbler (Acrocephalus sechellensis) translocation".Journal of Ornithology.159(2): 439–446.doi:10.1007/s10336-017-1518-8.S2CID4519848.
- ^Leisler, Bernd; Petra Heidrich; Karl Schulze-Hagen; Michael Wink (1997). "Taxonomy and phylogeny of reed warblers (genusAcrocephalus) based on mtDNA sequences and morphology ".Journal of Ornithology.138(4): 469–496.Bibcode:1997JOrni.138..469L.doi:10.1007/BF01651381.S2CID40665930.
- ^Helbig, Andreas; Ingrid Seibold (1999). "Molecular Phylogeny of Palearctic–AfricanAcrocephalusandHippolaisWarblers (Aves: Sylviidae ".Molecular Phylogenetics and Evolution.11(2): 246–260.Bibcode:1999MolPE..11..246H.doi:10.1006/mpev.1998.0571.PMID10191069.
- ^Bairlein, Franz; Alström, Per; Aymí, Raül; Clement, Peter; Dyrcz, Andrzej; Gargallo, Gabriel; Hawkins, Frank; Madge, Steve; Pearson, David; Svensson, Lars (2006), "Family Sylviidae (Old World Warblers)", in del Hoyo, Josep; Elliott, Andrew; Christie, David (eds.),Handbook of the Birds of the World. Volume 11, Old World Flycatchers to Old World Warblers,Barcelona: Lynx Edicions, p. 635,ISBN978-84-96553-06-4
- ^abSkerrett A, Bullock I & Disley T (2001)Birds of Seychelles.Helm Field GuidesISBN0-7136-3973-3
- ^Dowset-Lemaire, Francoise (1994). "The song of the Seychelles WarblerAcrocephalus sechellensisand its African relative ".Ibis.136(4): 489–491.doi:10.1111/j.1474-919X.1994.tb01127.x.
- ^Richardson D. (2001)Species Conservation Assessment and Action Plan, Seychelles Warbler.Nature Seychelles.
- ^"Seychelles WarblerAcrocephalus sechellensis".BirdLife International.Retrieved24 August2015.
- ^Komdeur J, Pels M (2005)."Rescue of the Seychelles warbler on Cousin Island, Seychelles: The role of habitat restoration".Biological Conservation.124(1): 15–26.Bibcode:2005BCons.124...15K.doi:10.1016/j.biocon.2004.12.009.
- ^Komdeur, Jan (1994)."The Effect of Kinship on Helping in the Cooperative Breeding Seychelles Warbler (Acrocephalus sechellensis)"(PDF).Proceedings: Biological Sciences.256(1345): 47–52.Bibcode:1994RSPSB.256...47K.doi:10.1098/rspb.1994.0047.JSTOR49592.S2CID54796150.
- ^Komdeur, J. (1994)."The Effect of Kinship on Helping in the Cooperative Breeding Seychelles Warbler"(PDF).Proceedings of the Royal Society.256(1345): 47–52.doi:10.1098/rspb.1994.0047.S2CID54796150.
- ^Komdeur, J. (1992)."Experimental Evidence for helping and hindering by previous offspring in the cooperative-breeding Seychelles warblerAcrocephalus sechellensis"(PDF).Behavioral Ecology and Sociobiology.34(3): 175–186.doi:10.1007/BF00167742.S2CID35183524.
- ^Komdeur, J. (1992). "Importance of habitat saturation and territory quality for evolution of cooperative breeding in the Seychelles warbler".Letters to Nature.358(6386): 493–495.Bibcode:1992Natur.358..493K.doi:10.1038/358493a0.S2CID4364419.
- ^Davies, N. B., Krebs J. R., West, S. A. (2012).An Introduction to Behavioural Ecology.Fourth Edition. West Sussex, UK: Wiley-Blackwell.
- ^Komdeur, J.; Magrath, M. J.; Krackow, S (2002)."Pre-ovulation control of hatchling sex ratio in the Seychelles warbler".Proceedings of the Royal Society.269(1495): 1067–1072.doi:10.1098/rspb.2002.1965.PMC1690984.PMID12028765.
External links
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