Behavioral observations on the White-breasted Thrasher (Ramphocinclus brachyurus brachyurus): conservation implications

Abstract

The White-breasted Thrasher (Ramphocinclus brachyurus brachyurus) is surviving at the tip of the Caravelle peninsula in Martinique, on a 5 km2 territory. Once widespread throughout the island, this passerine was on the verge of extinction in the 1950s but managed to recover. The creation of the Caravelle Nature Reserve in 1976 contributed to the protection of its habitat, but little is known about the factors behind the slow population growth registered in the past decades. A year-long ethological study was launched by the Regional Natural Park of Martinique (PNRM) in order to understand the status of this endangered species. In spite of some limitations, original observations shed new light on the behavior of this endemic species. New calls and a song were identified for the White-breasted Thrasher. The study highlights seasonal variations in the bird’s feeding behaviors and some behavioral plasticity in its reproductive strategies. Individuals appear to be exposed to strong predation pressure, especially during the breeding season. The confirmation of the modus operandi of rats against White-breasted Thrashers’ nests should help improve the conservation policy of this bird.

Habitat suitability models indicate the White-breasted ThrasherRamphocinclus brachyurusoccupies all suitable habitat in Saint Lucia

“…The species is territorial, and family groups consist of two breeders and 0-4 non-breeding helpers (Temple et al 2006, 2009, Mortensen 2009). The species is a habitat specialist; it is found only in coastal deciduous seasonal forest on the Caravelle Peninsula in Martinique (14°44’N, 60°93’W; Gros-Desormeaux et al 2014) and in two areas in Saint Lucia, the Mandelé and Iyanola ranges (13°53’N, 60°53’W and 13°59’N, 60°53’W, respectively; BirdLife International 2015) (Figure 1). These inhabited areas are not large; in Iyanola, where there are 100–200 birds (Felix et al 2014), White-breasted Thrashers are found in riparian forest primarily in the steep ravines that separate scrub habitat on ridge tops, and consequently they occupy only 62–126 ha (3.6–7.4%) of the 1,700 ha Iyanola range (Temple 2005).…”

Morphological Variation in the Martinican Subspecies White-Breasted Thrasher (<i>Ramphocinclus brachyurus brachyurus</i>)

“…Observations of White-breasted Thrashers appear to be more frequent in sloping wooded areas in alluvial basins. This is why White-breasted Thrashers are considered highly specialized in this type of habitat [13]. Due to the steep topography of the area, we selected two accessible sampling sites: A protected area, the Caravelle Nature Reserve, and a location known as "Morne Pavillon" (Figure 2).…”

“…Indeed, while the Martinique subspecies appears to be the most vulnerable because of its small population size and its restricted distribution of 5 km 2 on the Caravelle Peninsula, most published scientific research has been carried out into its counterpart in Saint-Lucia [8]. Published scientific articles on the Martinique subspecies consist of old articles describing the species [9], an article on the genetics of the species including samples from both subspecies [10], two articles on methods for detecting individuals and habitat characterization [11] [12], and an article describing the behavior of the R. b. brachyurus [13] Most of the information corresponds to institutional reports contained in expert reports [14]. None of the research provides a precise morphological description of R. b. brachyurus.…”

Current status of the Endangered White-breasted Thrasher (<em>Ramphocinclus brachyurus</em>), a dry forest songbird endemic to Saint Lucia and Martinique

“…The White-breasted Thrasher was considered to be a more common and widespread species in the 19th century compared to today (Danforth 1935, Diamond 1973, Keith 1997, Temple 2005, Gros-Desormeaux et al 2015. By the early 20th century, James Bond was already describing the species as "a very rare bird" (Bond 1928:536), writing, "I was told by an old hunter that 'the gorge-blanc' was at one time not uncommon in the southern mountains of Saint Lucia.…”

“…This extremely small and increasingly fragmented range is the justification for the species' IUCN status of Endangered (BirdLife International 2017). The call for White-breasted Thrasher research and conservation has been answered in part by field studies of the species' geographic range (Temple 2005), habitat requirements (Temple 2005), demography (Temple 2005, Mortensen 2009, Mortensen and Reed 2016, behavior (Temple et al 2006, Mortensen 2009, Gros-Desormeaux et al 2015, and population size (Temple 2005, Young et al 2010; modeling of habitat suitability (White et al 2012, Sass et al 2017) and extinction risk (Mortensen and Reed 2016); and the completion of the first conservation plan for the Saint Lucia subspecies (Felix et al 2014). Here we review the existing body of work on the White-breasted Thrasher, and discuss anticipated environmental changes and conservation objectives with a particular focus on the Saint Lucia subspecies.…”