SCI No

Restringido

Knowledge of population structure is fundamental when analysing the spatial distribution of and habitat selection in sex classes. The aim of this work was to describe the structure in terms of its sex ratio of a population of Water Rail Rallus aquaticus wintering in a tidal reed bed in Urdaibai (N Spain). Sampling was carried out during winter 2012–2013. Overall, 20 Water Rails were captured and the sex was molecularly determined in 19. Apart from one male, all the Water Rails (94.7%) were females. Assuming that males are the dominant sex and thus have priority access to optimal habit, one plausible explanation for this unusual pattern is that tidal reed beds could be a suboptimal habitat occupied by the subordinate sex (females). Alternatively, tidal reed beds may be sufficiently good-quality habitat but males may maintain their breeding territories elsewhere. Capture-associated biases were excluded. When considering biometrics, it seems unlikely that our Water Rails are winter visitors from northern regions.

Bravo, A., Esparza, X., Saéz de Adana, E., Schmitz-Ornés, A., Arizaga, J. 2014. Only females! An unexpected sex-biased population of wáter rails Rallus aquaticus wintering in a tidal marsh in the North of Spain. Rev. Cat. Ornitol. 30: 86-89