Habitat selection of two locally sympatric species ofEmberiza buntings (E. citrinella and E. hortulana)

Abstract

The Yellowhammer (Emberiza citrinella) and the Ortolan Bunting (E. hortulana) are locally-sympatric on a burned forest area in Norway where we investigated whether they differed in habitat selection. Territories of Ortolan Buntings were in areas with lower vegetation density than those of Yellowhammers, and as a consequence they tended to be in areas with shorter trees and further from farmland than Yellowhammers. A previous study in the same area found that Ortolan Buntings used farmland up to 2.7 km from their territories for foraging, and here we report that Yellowhammers also used farmland outside territories. Overall, Yellowhammers settled in areas with denser vegetation, which were closer to attractive farmland feeding areas, than Ortolan Buntings. The differences in habitat choice did not result from competitive exclusion of the migratory Ortolan Buntings by the resident and heavier Yellowhammers close to farmland, for (1) interspecific territory overlap was larger than intraspecific overlap, (2) few observations of interspecific aggression were made, and (3) playback of song elicited no interspecific responses. Thus, settlement of Ortolan Buntings was not restricted by Yellowhammers, and their differences in habitat were apparently due to different preferences. The observation that both species obtained food outside territories in another habitat argues against food resource partitioning being the cause of differences in nesting habitat. Instead, we argue that nest site partitioning may play a role in nesting habitat segregation between these sympatric species.