Current status of the Endangered White-breasted Thrasher (Ramphocinclus brachyurus), a dry forest songbird endemic to Saint Lucia and Martinique
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Abstract: The Eastern Caribbean islands of Martinique and Saint Lucia are home to the Endangered White-breasted Thrasher (Ramphocinclus brachyurus brachyurus in Martinique and R. b. sanctaeluciae in Saint Lucia). This species is among the most threatened of Caribbean birds, with fewer than 1,500 individuals range-wide. Here we review current research on its distribution, demography, behavior, and population size, as well as ongoing threats and conservation work. The thrasher is restricted to three areas of dry forest within its two-island extent: the Caravelle Peninsula in Martinique, and its Saint Lucia Iyanola and Mandelé ranges. On both islands, the species was once more widespread and abundant than it is today, though by the early 20th century, it was described as “a very rare bird” by the ornithologist James Bond. The Saint Lucia Mandelé range, discovered in the mid-1990s, now holds the largest extant population for the species, supporting almost 75% of the global population. Recent extensive fieldwork in this range established that the thrasher has relatively low nesting success and high adult survival, a pattern seen in many tropical birds. This work also documented the unusual breeding behavior of the species, cooperative breeding, whereby some individuals delay dispersal and breeding to help raise non-descendant kin. A likely consequence of this behavior is short dispersal distances; for example, there is no evidence that individuals move between islands or between the two ranges in Saint Lucia that are separated by only 3 km. A lack of gene flow has consequences for conservation planning and for species limits reassessment. The greatest threats to the White-breasted Thrasher are habitat loss and fragmentation, habitat degradation, and pressure from non-native mammalian predators. This first threat is the most acute in Saint Lucia, where there is a lack of protected habitat and ongoing habitat loss, and the last is the most acute in Martinique, where 50% of the species’ range has been formally protected since the 1970s. These threats recently motivated the creation of the first conservation plan for the Saint Lucia subspecies.
Keywords: Caribbean, habitat loss, island, Ramphocinclus brachyurus, threatened species, tropical birds, White-breasted Thrasher
Resumen: Estado actual de Ramphocinclus brachyurus, paseriforme endémico y En Peligro del bosque seco de Santa Lucia y Martinica—Las islas de Martinica y Santa Lucia, del Caribe Oriental, son el hogar del ave En Peligro Ramphocinclus brachyurus (R. b. brachyurus en Martinica y R. b. sanctaeluciae en Santa Lucia). Esta especie está entre las más amenazadas de las aves caribeñas, con menos de 1.500 individuos en todo su rango de distribución. Revisamos las investigaciones actuales que existen sobre su distribución, demografía, conducta y tamaño poblacional, así como las amenazas actuales y el trabajo de conservación. Esta especie está restringida a tres áreas de bosque seco dentro de su rango de distribución en las dos islas: la península de Caravelle en Martinica y las regiones de Iyanola y Mandelé en Santa Lucia. En ambas islas, la especie fue más abundante y tuvo una distribución más amplia que la que se conoce hoy en día; aunque a principios del siglo 20, el ornitólogo James Bond la describió como “un ave muy rara”. La region de Mandelé en Santa Lucia, descubierta a mediados de los 90, contiene actualmente la población más grande de esta especie, soportando casi el 75% del estimado global. Un amplio y reciente trabajo de campo en esta zona comprobó que esta especie tiene un éxito de nidificación relativamente bajo y una alta supervivencia adulta, un patrón visto en muchas especies de aves tropicales. Este trabajo también documentó la inusual conducta de cría de esta especie, la cría cooperativa, donde algunos individuos demoran la dispersión y la cría para ayudar en la cría de descendientes no emparentados. Una probable consecuencia de esta conducta son distancias de dispersión cortas; por ejemplo, no existe evidencia de que los individuos se muevan entre islas o entre las dos regiones de Santa Lucia que están separadas por sólo 3 km. La ausencia de flujo genético tiene consecuencias para los planes de conservación y la revaluación de los límites para esta especie. Las mayores amenazas para el Ramphocinclus brachyurus son la pérdida de hábitat, la fragmentación y ladegradación del hábitat y la presión por parte de mamíferos depredadores no nativos. La primera amenaza es la más grave en Santa Lucia, donde hay una falta de hábitat protegido y una constante pérdida de hábitat; y la más grave en Martinica es la última, donde el 50% del rango de distribución de la especie ha sido protegido formalmente desde la década de los 70. Estas amenazas motivaron recientemente la creación del primer plan de conservación para la subespecie de Santa Lucia.
Palabras clave: aves tropicales, Caribe, especie amenazada, isla, pérdida de hábitat, Ramphocinclus brachyurus
Résumé: Situation actuelle du Moqueur gorge-blanche (Ramphocinclus brachyurus), espèce En danger endémique des forêts sèches de Sainte-Lucie et de la Martinique—Les îles de la Martinique et de Sainte-Lucie dans l’est de la Caraïbe abritent une espèce En danger, le Moqueur gorge-blanche (Ramphocinclus brachyurus brachyurus en Martinique et R. b. sanctaeluciae à Sainte-Lucie). Cette espèce est parmi les oiseaux caribéens les plus menacés, avec moins de 1.500 individus dans l’ensemble de son aire de répartition mondiale. Nous examinons ici les recherches actuelles sur la répartition, la démographie, le comportement et la taille de la population, ainsi que les menaces actuelles et les travaux de conservation en cours. Le Moqueur gorge-blanche est limité à trois zones de forêt sèche sur les deux îles : la péninsule de la Caravelle en Martinique et les zones de Iyanola et de Mandelé à Sainte-Lucie. L'espèce a été autrefois plus répandue et plus abondante sur les deux îles qu’elle ne l’est aujourd’hui, mais au début du XXe siècle, elle était décrite comme « un oiseau très rare » par l’ornithologue James Bond. Son occupation de la zone de Mandelé à Sainte-Lucie, découverte au milieu des années 1990, comprend actuellement la plus grande population existante, avec près de 75% de la population mondiale. Le travail de terrain mené récemment sur cette zone a montré que le Moqueur gorge-blanche présente un succès de reproduction relativement bas et une survie élevée des adultes, un schéma observé chez de nombreux oiseaux tropicaux. Ce travail a également documenté le comportement de reproduction inhabituel de l’espèce, l’élevage coopératif, dans lequel certains individus retardent leur dispersion et leur reproduction pour aider à l’élevage de jeunes qui ne sont pas leurs descendants. Une conséquence probable de ce comportement est la faible distance de dispersion ; il n’y a actuellement aucune preuve que les individus se déplacent entre les îles ou entre les deux zones d’occupation à Sainte-Lucie, qui ne sont séparées que de 3 km. L’absence de flux génétique a des conséquences pour la planification de la conservation et pour la réévaluation des limites de l’espèce. Les plus fortes menaces pesant sur le Moqueur gorge-blanche sont d’une part la perte, la fragmentation et la dégradation de ses habitats et d’autre part la pression des mammifères prédateurs non indigènes. Cette première menace est la plus grave à Sainte-Lucie où il y a actuellement un manque de protection et une perte de ses habitats, et la seconde est la plus sévère en Martinique où 50% de l’aire de répartition de l’espèce est formellement protégée depuis les années 1970. Ces menaces ont récemment motivé la création du premier plan de conservation de la sous-espèce de Sainte-Lucie.
Mots clés: Caraïbe, espèces menacées, île, Moqueur gorge-blanche, oiseaux tropicaux, perte d’habitat, Ramphocinclus brachyurus
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