Habitat selection and coexistence in wintering passerine steppe birds

摘要

This study evaluates the relative contributions of landscape features and biotic (conspecific and hetero-specific) relationships to habitat selection of three sym-patric passerine species, Skylark (Alauda arvensis), Corn Bunting (Emberiza calandra) and Calandra Lark (Mela-nocorypha calandra) during winter. Between December 2007 and January 2008, winter populations of the three species were censused in three Central Spanish locations by means of linear transects (n = 60). An explanatory model-averaging approach was used to determine the weight and effect of different landscape and biotic variables in each species' habitat selection patterns using their respective abundance as the dependent variable. A deviance partitioning approach was used to determine the relative contributions of these two sets of predictors. Only the Calandra Lark showed a significant influence of landscape variables, preferring relatively simplified landscapes with a low density of field margins. The three species showed preferences for proximity of con- and heterospecifics. This cari be explained in relation to their gregarious behaviour during this season, which results in the formation of big multispecific flocks that confer some individual advantages (such as a better feeding efficiency or anti-predator benefits). This is also supported by the results of the deviance partitioning analysis, which showed the much higher importance of biotic interaction factors in relation to the contribution of landscape (which is negligible) for Skylarkand Corn Bunting. However, for Calandra Lark, although biotic interactions are also the most important factors, both landscape and the combined effect of landscape and biotic interactions are slightly larger. Finally, we also found an effect of flock size on habitat selection, so that, for bigger flocks, habitat and biotic interaction factors will have a weaker effect on abundance and selection patterns.