Data Zone
Justification of Red List category
This species has a very small range, which is continuing to decline as coastal dry woodland is cleared to make way for agriculture, housing and especially tourism developments. Consequently, the species warrants listing as Endangered.
Population justification
The population is estimated to number 200-400 individuals on Martinique (Temple 2005; AOMA 2008) (equivalent to 133-267 mature individuals) and 1,130 mature individuals on St Lucia (1,030 in Mandelé and 100 in Iyanola [M. Morton in litt. 2016]), giving a range of 1,293-1,397 mature individuals, rounded here to 1,300-1,400 mature individuals.
Trend justification
Recently, the rate of decline increased owing to the construction of a hotel resort that destroyed the habitat of 25% of the global population. Moderately rapid to rapid declines are therefore estimated. The largest subpopulation (on St Lucia) may be undergoing an even more rapid decline (M. Morton in litt. 2012), having decreased by 56% from 1,766 individuals in 2006 to 760 in 2011 (Morton 2012). Projecting the observed decline in this subpopulation into the future (up to 2024) suggests that the population could decline by 80% in less than ten years (Felix et al. 2014). A study modelled the Mandelé subpopulation on St Lucia (c.84% of the total population) and estimated a reduction in the number of birds from 1,637 to 1,440 between 2007 and 2015 (Morton et al. 2016). It also predicted a decline of 85% of this subpopulation and of 57-71% in the global population across the following 15 years, which equates to a ~52-66% decline over three generations (13.2 years). These predictions do not take into account the potential continuation of development at the hotel resort or the planned adjacent wind farm, or recently increased threats from timber extraction and feral pigs; so actual declines may be greater than those projected.
This species occurs as two subspecies which differ in plumage, measurements and vocalisations. The nominate race is restricted to the Caravelle Peninsula on Martinique (to France) (Bulens et al. 1994; P. Feldmann and P. Villard in litt. 1998; H. J. Temple in litt. 2003; Temple 2005), an area of c. 5 km2. Race sanctaeluciae occurs on the north-east coast of St Lucia between the Marquis River Valley and Frigate Island Refuge (Keith 1997; J. D. Gilardi in litt. 1999). Until 1993, the thrasher was thought to be restricted to the northern part of this area (Marquis-Dennery Knob), and population estimates and censuses in 1971, 1987, 1992 and 2003 suggested that the population in this northern area may be declining (J. D. Gilardi in litt. 1999; H. J. Temple in litt. 2003). In 1993, thrashers were discovered near the Frigate Island Refuge, and recent research suggests that this site (Mandelé) holds c.85% of the global population. A comprehensive programme of searches on Martinique found no new subpopulations anywhere else on the island and it is considered that R. brachyurus occupies virtually all suitable habitat on St Lucia (Sass et al. 2016). Surveys in 2003 and 2004 indicated a global population of 1,300-2,600 breeding adults, 1,100-2,400 on St Lucia and c.200 on Martinique (Temple 2005). In 2006 and 2007, the St Lucia population still numbered about 1,200-1,700 individuals (Young et al. 2010; Morton et al. 2016). By 2016, the population on Saint Lucia was estimated to be 1,130 mature birds, with 1,030 in the southern (Mandelé) population (Morton et al. 2016).
On both islands, the species inhabits dry and semi-dry woodland and scrub with abundant leaf-litter, often in areas with a clear understorey but sometimes in dense thickets. In the northern part of its range on St Lucia (Petite Anse-Dennery Knob), it tends to occur along ravines and river-valleys, but in the rest of its range on St Lucia and Martinique it also occurs on dry hillsides well away from streams. It tolerates a degree of habitat degradation and is often found in secondary woodland and scrub, but although it is occasionally seen in clearings and smallholders' crop-fields, it does not breed in these man-made habitats (Temple 2005). A habitat suitability model indicated in 2016 that the species occupies virtually all suitable habitat on St Lucia and that birds in the northern range occupy marginal habitat (Sass et al. 2016). It typically forages on the ground for invertebrates, small frogs and lizards, also taking berries (Keith 1997; Raffaele et al. 1998). Breeding apparently coincides with the onset of the rainy season, and the bulky open-cup nest is placed 0.5-3 m from the ground, usually in the fork of a thin sapling (Keith 1997; J. D. Gilardi in litt. 1999; H. J. Temple in litt. 2003). Eggs (usually two) are laid from May until August, and thrashers may rear more than one successful brood in a season (Keith 1997; J. D. Gilardi in litt. 1999; H. J. Temple in litt. 2003). The species sometimes breeds cooperatively; one-third to two-thirds of nests have helpers, which apparently retain offspring from previous years, and may be either male or female (Temple et al. 2009; H. J. Temple in litt. 2003; Mortensen 2016). Chicks leave the nest before fledging, and continue to be fed on the ground (J. D. Gilardi in litt. 1999). On St Lucia, nesting success was 44% in 1997, 55% in 2001, 74% in 2002 and 44% in 2003, suggesting normal levels of nest predation for a tropical passerine (J. D. Gilardi in litt. 1999; H. J. Temple in litt. 2003). The species is highly sedentary, and may reside permanently on or near breeding territories (J. D. Gilardi in litt. 1999). It occurs at high densities within its restricted range (Temple 2005), suggesting that it may be at carrying capacity, with population increases being unlikely to occur unless more habitat is created (H. J. Temple in litt. 2006).
The main threat to this species is habitat loss, perhaps compounded by the impact of predation by introduced mammals. On Martinique, habitat loss during the colonial era means that the species now has a tiny population restricted to a very small area (Temple 2005). Most of this is effectively protected, although some losses to agriculture, charcoal-burning and housing development continue (H. J. Temple in litt. 2006). On St Lucia, on-going habitat degradation and loss is caused by agriculture, charcoal-burning and wood-cutting, and there are potentially devastating plans to build a highway through the centre of the thrasher's range (J. D. Gilardi in litt. 1999). The Le Paradis Resort and Golf Course is being constructed on St Lucia on a site that is estimated to hold c. 25% of the global population (Temple 2005), and tourism development companies will soon own land equivalent to 35% of the global extent of occurrence (Young et al. 2010). By 2008, 84 ha (12% of the range of St Lucia's southern subpopulation) had been cleared for golf course/hotel construction (M. Morton in litt. 2012). Construction was then halted, but it still has planning permission; were it to be completed, a projected 248 ha (34% of the southern range) would be lost (M. Morton in litt. 2012; Felix et al. 2014). Currently, 20% of the species's habitat within its range has been lost through such development, a 16% loss of habitat on St Lucia in total (Mortensen and Reed 2016). In addition, in 2015 a wind farm development was proposed (with construction projected to start in December 2016), which will occupy another 16% of the southern range. The operational footprint will be lower than this percentage, but during the construction phase it seems likely there will heavy disturbance across this whole area (which includes the area of highest nesting density) (M. Morton in litt. 2016). In the northern part of the range on St Lucia, planning permission is being sought for two large estates, the development of which would result in approximately 1,000 ha (60%) of the northern range being lost (M. Morton in litt. 2012). Between 2006 and 2009, the encounter rate of this species declined by 55% within the Le Paradis tourist development site, whilst remaining comparatively stable (6% decline) outside the site for the southern subpopulation (White et al. 2012).
Small Indian Mongoose Herpestes auropunctatus and rats Rattus spp. have been present on both islands since before 1900, implying that the thrasher is able to coexist with these predators, but they may place an unwelcome additional burden on an already small population. Introduced opossums Didelphis marsupialis and domestic cats pose additional threats (Felix et al. 2014). Nest-monitoring on St Lucia suggests that levels of nest predation by introduced mammals are not excessive, but the situation could be different on Martinique, where rats and mongoose may be more abundant: further research is required. In recent years, informal agriculture has resulted in habitat conversion in the species's southern range in Saint Lucia and is also the putative cause of incursions by feral pigs from the adjacent forest reserve. Feral pigs (Sus scrofa) are degrading the habitat of the White-breasted Thrasher and may predate fledglings (M. Morton in litt. 2016). Other informal uses include the large scale removal of small stems used by White-breasted Thrashers for nesting, and increased dumping of garbage. Soil erosion after clearance of forest for golf course fairways (currently abandoned) has largely prevented forest regeneration. Because the thrasher is confined to narrow areas along the Windward coast, a major hurricane could have a severe impact (H. J. Temple in litt. 2003; Mortensen et al 2017). Additionally, studies have shown the species to be a poor disperser (Temple et al. 2006), and it is likely that movement between the two subpopulations on St Lucia is limited, restricting the potential for one population to "rescue" the other from a significant decline (Mortensen 2016).
Conservation and Research Actions Underway
The well-protected (albeit small) Caravelle Nature Reserve covers part of the species's range on Martinique. The white-breasted thrasher is legally protected on St Lucia (under Schedule 1 of the 1980 Wildlife Protection Act (revised 1980)), but very little of its St Lucian range falls within a protected area (just 4% [Mortensen et al. 2017]). Four small areas fall under the protection of the St Lucia Forest, Soil and Water Conservation Act which makes it an offence to remove or damage trees within the area or to clear the land (Felix et al. 2014). On both islands, studies have been carried out to assess the population and threats, and on Martinique a plan exists to control introduced predators (Bulens et al. 1994; Temple 2005; P. Feldmann and P. Villard in litt. 1998). Banding birds has facilitated detailed ecological and population research (Temple 2005; P. Feldmann and P. Villard in litt. 1998; J. D. Gilardi in litt. 1999; H. J. Temple in litt. 2003; Mortensen 2016). A demographic population projection model for the St Lucia southern population (Mortensen and Reed 2016) found that extinction risk increased when the habitat area expected to remain following planned resort construction is factored in. Improving survival estimates and determining the cause(s) of juvenile mortality were identified as research priorities. A genetic study has provided the first description of genetic diversity and population structure of the species (Mortensen 2016) and showed large differences between subspecies, concordant with plumage, biometric, and vocalization differences. A draft action plan for the species was released in 2014 (Felix et al. 2014). By 2020, the 7-year plan aims to have reversed declines so that the population is increasing and at least three sites in St Lucia are being managed for the species. In 2015, the Government of Saint Lucia started a project that proposes to effect forest restoration in the Iyanola area. An awareness-raising campaign on the white-breasted thrasher and its habitat in Saint Lucia was started in 2016.
Conservation and Research Actions Proposed
Monitor both island populations to assess trends. Establish protected areas and effectively protect coastal dry woodland and scrub within the thrasher's range on St Lucia, and prevent further habitat losses on Martinique. Allow adjacent farmland to regenerate into scrub woodland, providing additional habitat and allowing populations to expand. Conduct further research into the impact of predators on Martinique, and implement the predator control plan if deemed necessary. Control predators on St. Lucia (Young et al. 2010). Enact legislation on St Lucia to protect critical wildlife sites. Consult with the hotel developers and stakeholders on St Lucia to protect suitable areas of thrasher habitat in a private reserve (P. Cosgrove in litt. 2007). Safeguard patches of dry forest to the west and north of the Le Paradis tourism development site in Mandelé. Quantify the impact of the Le Paradis development. Preserve mature dry and riparian forest within the tourism development site in Mandelé (Young et al. 2010). Research the taxonomic status of the two subspecies. Improve mortality estimates and determine the cause(s) of juvenile mortality (Mortensen and Reed 2016).
23-25 cm. Dark brown-and-white bird with long bill. Dark brown upperparts. White underparts. Red iris. Long bill, decurved near tip. Immature, entirely brown and develops white breast-patch with age. Similar spp. Grey Trembler Cinclocerthia gutturalis is larger, less two-toned, grey above and has white iris. Voice Limited repertoire of short, harsh calls, occasionally a musical tee-rou. Alarm call a harsh tschhhh. Juveniles located on ground by thin tseep calls.
Text account compilers
Wheatley, H., Everest, J.
Contributors
Ashpole, J, Benstead, P., Cosgrove, P., Feldmann, P., Gilardi, J., Isherwood, I., Mahood, S., Morton, M., Pople, R., Sharpe, C.J., Temple, H., Villard, P., Wege, D. & Westrip, J.R.S.
Recommended citation
BirdLife International (2024) Species factsheet: White-breasted Thrasher Ramphocinclus brachyurus. Downloaded from
https://datazone.birdlife.org/species/factsheet/white-breasted-thrasher-ramphocinclus-brachyurus on 24/12/2024.
Recommended citation for factsheets for more than one species: BirdLife International (2024) IUCN Red List for birds. Downloaded from
https://datazone.birdlife.org/species/search on 24/12/2024.