Habitat selection, home range and population size of Baillon’s Crake Zapornia pusilla in the Senegal Delta, north-west Senegal

Knowledge of a species' ecological requirements is a prerequisite for effective conservation, particularly if the species is assumed to be declining due to modification of its primary habitats. Information about habitat suitability allows both the inference of specific habitat management measures as well as population size estimates which can facilitate the setting up of conservation priorities. As one of the least known Palaearctic breeding birds, the current knowledge of Baillon's Crake Zapornia pusilla comprises only very general information about the species' ecological requirements, habitat selection, extent and dynamics of home ranges or population densities within its Palaearctic-Afrotropical range. We used a multi-scale approach to assess the species' habitat requirements in the Senegal River Delta, north-west Senegal. At the individual level, we calculated Manly selection indices for 17 radio-tracked Baillon's Crakes, allowing for different levels of resource availability. Considering the entire Djoudj area including the Parc National des Oiseaux du Djoudj (PNOD), we modelled presence probability as well as population density of Baillon's Crakes based on high-resolution satellite images and capture data from field surveys in 2009-2013. Using 95% kernels, home range size was on average 1.77 +/- 0.86 ha with significant differences between habitats. Both at the individual as well as population level, Baillon's Crakes preferred edge structures, selecting for trampling paths and edges along open water bodies as well as boundaries of specific vegetation stands while species composition was of less importance. Based on the regression models, we identified 9,516 ha of suitable habitat within the Djoudj area and a potential population size of 10,714 individuals (range 3,146-17,408). Although global population estimates are highly tentative, we assume the Senegal River Delta and the PNOD of outstanding significance for African and possibly also European populations of Baillon's Crake.