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White-breasted thrasher

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White-breasted thrasher
In Martinique
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Aves
Order: Passeriformes
Family: Mimidae
Genus: Ramphocinclus
Lafresnaye, 1843
Species:
R. brachyurus
Binomial name
Ramphocinclus brachyurus
(Vieillot, 1818)

The white-breasted thrasher (Ramphocinclus brachyurus) is a species of bird in the family Mimidae. Semper and Sclater (1872) describe the white-breasted thrasher as an "inquisitive and noisy bird" that would often "keep up a constant warning chatter, and throw itself about in all sorts of contortions" when being disturbed.[2] It is endemic to Martinique and Saint Lucia, found only on these two islands of the Lesser Antilles. This resident species is easy to find within its range; however, it is classified as endangered by the IUCN Red List of Threatened Species mainly due to its restricted habitat.[3]

Description

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The white-breasted thrasher is in average 23 to 25 cm long, and weight from 48 to 60 g depending on sex and subspecies.[4] An adult bird has a dark brown plumage with a white throat, breast, and belly. Its dark beak is long and slightly decurved towards the tip. Several dark bristles are located around the lores, between the red eyes and nostrils of the bird.[4] This medium-sized passerine has long and strong black legs and can live up to 7–8 years.[5] Males and females are sexually monomorphic, thus identical in size and coloration. This bird is difficultly sexed by hand or sight due to sexual monomorphism. Males and females have the same plumage and only breeding females can be identified during breading season by their brood patch.[6]

The plumage of an immature white-breasted thrasher is uniformly brown, with a brown throat and a greyish belly. The white patch on its breast will develop with age, around a month later. When the bird is in its first year, it can be differentiated to an adult bird by the rusty brown colour of its upper-parts, and its brownish eye color.[6]

Taxonomy

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The white-breasted thrasher belongs to a monophyletic group and is the only member of genus Ramphocinclus[7].

There are two known subspecies of white-breasted thrasher:[6]

  • Ramphocinclus brachyurus brachyurus,
  • Ramphocinclus brachyurus sanctaeluciae

Until now, the two subspecies are each restricted to their own habitat location, but they can also be differentiated by their size and coloration. Indeed, R. b. sanctaeluciae is larger, darker, and show a greater sexual dimorphism than R. b. brachyurus.[8]

Habitat and distribution

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Distribution

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Because the white-breasted thrasher is endemic to two islands of the Lesser Antilles, its range is dangerously small for species survival.

  • The nominal subspecies, R. b. brachyurus, is only found in Martinique, where its habitat is restricted to a 5 km^2, now protected, area called the Caravelle Peninsula.[9]
  • Whereas R. b. sanctaeluciae inhabits Saint Lucia, which is south of Martinique. Two different populations of this subspecies are distinguished by habitat location on the island: a northern population located in Iyanola municipality and a southern one in Mandelé municipality.

There is no evidence of white-breasted thrasher movement between the two islands.[10]

Habitat

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The white-breasted thrasher prefers deciduous tropical dry forests and shrub lands, although the northern population of R. b. sanctaeluciae lives along ravines and river-valleys.[4]

The semi wooded habitats carefully selected by this habitat specialist must be located within 2 km of the coast, and up to 200 m above sea level.[4] Low canopy shrubs and clear spaces are avoided by both subspecies because of predation, especially during breeding.[5] Soils with an abundant leaf-litter are also favoured for feeding.

Behaviour

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Diet

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The white-breasted thrasher's diet is adaptable and goes from animal proteins to fruits. Feeding habits depend on what's available to the bird according to environmental conditions. White-breasted thrashers are ground eaters. They forage mainly on leaf litter fauna, looking for insects or berries. They also have the ability to regurgitate a whole berry and spit out seeds to save it for a later meal.[4][6][11]

Predators

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Because white-breasted thrashers are ground eating birds, they are mostly vulnerable to small mammals attacks, but they are also often victim of egg predation. The predator list differs for each subspecies, as the two islands don't have the same fauna and introduced species. R.b.sanctaeluciae predators are the boa constrictor (Constrictor orophias), the common opossum (Didelphis marsupialis), and the broad-wing hawk (Buteo platypterus) whereas R.b.brachyrus predators are rats (Rattus rattus), the introduced small Indian mongoose and cats (Felis silverstris catus).[10][12]

Vocalization

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Vocalization repertoire of the white-breasted thrasher is limited which is surprising for a species that belongs to Mimids. The white-breasted thrashers often vocalize short and harsh calls, and sometimes a musical "tee-rou". Alarm calls are harsh "tschh" on Saint Lucia, and "grok grok" on Martinique. They are used between birds to warn each other when a threat is perceived. Juveniles are located by thin "tseep" calls.[3][11]

Reproduction

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The white-breasted thrasher's breeding season starts mid-April and lasts until the end of September. A breeding bird can have up to four successive broods in one breeding season and the average clutch size varies from 1 to 3 eggs.[11] Birds usually live in pairs and build voluminous nests in high trees from 1.5 to 5 m above the ground.[6] Before using a nest, a pair of birds usually build several of them. Each individual takes turn in nest-building tasks. For instance, each bird sits in the nest, in turns, to adjust the inside part of it. White-breasted thrashers are thus called cooperative breeders.[10][13]

Because of egg predation, nesting failure is relatively high and white-breasted thrashers use an anti-predatory strategy that consists of keeping their nests clean of eggshells and fecal sacs to reduce nest detection.[11]

Conservation status

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The white-breasted thrasher total population is estimated at 1900 individuals and is ranked as "endangered" according to the IUCN Red List.[3] The rate of decline of the population has largely increased due to habitat loss on both islands.[10][14] The white-breasted thrasher is able to coexist with some of its predators such as rats and mongooses. However, this predation places an additional burden on the already small thrasher population, especially in Martinique where rats and mongooses are more abundant. That is why organizations charged with environmental protection have started several programs such as rat extermination, a mongoose capture program, and also a program aimed at monitoring the reproduction success of the R. b. brachyurus (in which one of the tasks consists of fixing plastic bottles on nesting trees trunks, preventing predators from reaching the nest).[15]

References

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  1. ^ BirdLife International (2020). "Ramphocinclus brachyurus". IUCN Red List of Threatened Species. 2020: e.T22711137A179788434. doi:10.2305/IUCN.UK.2020-3.RLTS.T22711137A179788434.en. Retrieved 12 November 2021.
  2. ^ Semper JE, Sclater PL. 1872. Observation on the birds of St Lucia. Proceedings of the Zoological Society of London. 647-653.
  3. ^ a b c BirdLife International. 2012. Ramphocinclus brachyurus. TheIUCN RedList of Threatened Species. International Union for Conservation of Nature. Retrieved 29 September 2015.
  4. ^ a b c d e Benstead P, Isherwood I, Mahood S, Pople R, Sharpe C J, Temple H, Wege D. 2015. Species factsheet: Ramphocinclus brachyurus. BirdLife International; [cited 2015 Sept. 29]. Available from: http://www.birdlife.org
  5. ^ a b Gros-Désormeaux JR, Lesales T, Tayalay AG. 2012. Ethologie du moqueur gorge blanche Ramphocinclus brachyurus. Technical report. CIHENCE. Available from: http://www.pnr-martinique.com/wp-content/uploads/2012/11/rapport-ethologie_CIHENCE_11102012.pdf
  6. ^ a b c d e Mortensen J, Freeman K, Morton M. 2014. White-breasted Thrasher (Ramphocinclus brachyurus), Neotropical Birds Online. Ithaca: The Cornell Lab of Ornithology Neotropical Birds; [cited 2015 Sept. 29]. Available from: http://neotropical.birds.cornell.edu/portal/species/overview?p_p_spp=559116
  7. ^ Thomas M. Brooks; John D. Pilgrim; Ana S. L. Rodrigues & Gustavo A. B. Da Fonseca (2005). "Conservation status and geographic distribution of avian evolutionary history". In Andy Purvis; John L. Gittleman & Thomas Brooks (eds.). Phylogeny and Conservation. Conservation Biology. Vol. 8. Cambridge University Press. pp. 267–294. ISBN 978-0-521-82502-3.
  8. ^ John L. 1995. The St. Lucia White-breasted Thrasher Ramphocinclus brachyurus sanctaeluciae project report. Unpublished project report, St. Lucia Forestry Department, Castries, St. Lucia.
  9. ^ Caravelle peninsula [Internet]. 2007. Martinique (FWI): Life Cap Dom; [cited 2015 Sept. 29]. Available from: http://www.lifecapdom.org/sites-34/martinique-36/article/the-caravelle-peninsula?lang=en
  10. ^ a b c d Temple HJ, Hoffman JI, Amos W. 2006. Dispersal, philopatry and intergroup relatedness: fine-scale genetic structure in the White-breasted Thrasher, Ramphocinclus brachyurus. Molecular Ecology 15: 3449-3458.
  11. ^ a b c d Gros-Désormeaux JR, Lesales T, Tayalay AG. 2014. Behavioural Observations on the White-Breasted Thrasher (Ramphocinclus brachyurus brachyurus): conservation implications. ActaEthol. 18(2):197-208.
  12. ^ Gros-Désormeaux JR, Lesales T, Tayalay AG. 2007. Suivi du Moqueur Martinique (FWI): Parc Naturel Régional de la Martinique; [cited 2015 Sept. 29]. Available from: http://www.martinique.developpement-durable.gouv.fr/IMG/pdf/2007-2006_Suivi_Moqueur_Avifaune-RNCaravelle_2_clele2a75.pdf
  13. ^ Temple HJ, Hoffman JI, Amos W. 2009. Group structure, mating system and extra-group paternity in the co-operatively breeding White-breasted Thrasher Ramphocinclus brachyurus. Ibis 151(1):99-112.
  14. ^ Young RP, Baptiste TJN, Dornelly A, Temple H, Whitehead H, Young HG, Morton MN. 2010. Potential impacts of tourist developments in St Lucia on the Endangered White-breasted Thrasher Ramphocinclus brachyurus. Bird Conservation International 20(4): 354-364.
  15. ^ White-breasted Thrasher [Internet]. 2007. Martinique (FWI): Life Cap Dom; [cited 2015 Sept. 29]. Available from: http://www.lifecapdom.org
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