BRANTA — Helen J. Temple
Ecology, cooperative breeding and conservation of the White-breasted Thrasher Ramphocinclus brachyurus
Institution: University of Cambrdige, UK
Supervisors: M Brooke, N Collar (BirdLife)
Details: PhD 2005 (Completed)
Address: IUCN, 219c Huntingdon Road, Cambridge, CB3 0DL, UK (Apr 2006) Email
Subject Keywords: Behavioural ecology, conservation, cooperative breeding, social organisation, habitat selection, breeding biology, threatened species, endangered species, St Lucia, Martinique, Caribbean, West Indies
Species Keywords: White-breasted Thrasher Ramphocinclus brachyurus
The White-breasted Thrasher, a passerine bird which is unique to the West Indian islands of St Lucia and Martinique, is notable both for its unfavourable conservation status (it is classed as globally Endangered) and for its unusual reproductive behaviour (it is one of approximately 3% of the world’s avian species that breed cooperatively). In 2002-2004 I investigated the range, status, habitat requirements, breeding biology, demography and reproductive behaviour of the White-breasted Thrasher at field sites on the east coast of St Lucia. A small amount of comparative work was carried out on Martinique. In addition to this fieldwork, I used microsatellite genotyping to investigate the genetic structure of groups and populations. I estimate the global population of White-breasted Thrashers at 1300-2800 breeding adults occupying a total range of c. 13 km2. In the northern part of St Lucia, the population has apparently declined by more than 50% since 1971. White-breasted Thrashers are habitat-restricted, being found only in closed-canopy dry scrub, dry woodland, and areas transitional between the coastal dry woodland and the rainforest of the interior. White-breasted Thrashers live in groups of 2-4 adults (mean 2.4) and cooperate to raise 1-3 clutches of 1-3 eggs per year. Breeding occurred during the rainy season, from April to September. Mayfield nest success was within the typical range for tropical passerines, at 37%, and annual survival was high (0.87 for adults and 0.66 for juveniles). Breeding success correlated with group size, but this seemed to be due to improved predator defence, since cooperative groups did not provision at a greater rate than unassisted pairs. Predation was the principal cause of nest failure, with Boa Constrictors Boa constrictor orophias being the most frequently-recorded predator. White-breasted Thrasher groups are made up of a dominant breeding pair and 0-2 helpers of both sexes that are previous offspring of the dominant pair. Rates of extra-group paternity are low (6%) and within-group sharing was not recorded in this study. Juvenile males are philopatric whereas juvenile females disperse over longer distances: this leads to a very strong fine-scale genetic substructuring of the male (but not female) population, with high levels of relatedness (c. 0.25) between nearest-neighbour dominant males. The main cause of the White-breasted Thrasher’s decline is habitat loss, and conservation measures should focus on habitat protection and restoration.
Jin L., Temple H. J., Hoffman J. I., Shengjiang T. & Amos W. (2005) Polymorphic microsatellite DNA markers for the White-breasted Thrasher, Ramphocinclus brachyurus. Molecular Ecology Notes 6: 862.
Temple H. J., Hoffman J. I. & Amos W. (2006) Dispersal, philopatry and inter-group relatedness: fine-scale genetic structure in the White-breasted Thrasher Ramphocinclus brachyurus. Molecular Ecology 15: 3449-3458.