Habitat use and niche overlap of ground-nesting steppic birds

Abstract

Steppic habitats host an extremely high proportion of birds with unfavourable conservation status in Europe, such as larks. This research aims to both investigate habitat-lark relationships and assess the niche overlap among larks in southern Italy during the breeding season. Studied in particular were the Eurasian Skylark (Alauda arvensis), the Greater Short-toed Lark (Calandrella brachydactyla), the Calandra Lark (Melanocorypha calandra), the Crested Lark (Galerida cristata) and the Woodlark (Lullula arborea). During the 2012 breeding season, 301 point counts were carried out, and these were randomly placed in the study area according to a stratified sampling design. Resource selection probability functions were used to build two models for each species: (i) a binary logistic regression using the presence units as the dependent variable and (ii) a GLM with Poisson’s error distribution using the abundance of larks in each sampling point as the dependent variable. In the first model, the land cover in the cells of a 100-m-grid superimposed onto the study area was used as a covariate, whereas in the second model, the same covariate was measured, but in a 300-m-buffer around the sampling points. Finally, niche overlap was measured by Hurlbert’s Index with bootstrap resampling. Results showed that the Skylark, Short-toed Lark, Calandra Lark and Crested Lark are tightly associated with both non-irrigated crops and dry grasslands, with these species selecting areas in which both habitats are present in particular. Furthermore, there is a strong niche overlap at macrohabitat level among the species, with the exception of the Woodlark, which is an ecotonal species.