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.