Can a solitary avian species use collective detection? An assay in semi-natural conditions

Collective detection (e.g., enhanced predator detection through the vigilance of conspecifics) is expected to have evolved particularly in social species. However, we assessed the degree to which an avian territorial species (California towhee Pipilo crissalis) would use social cues about predation in a semi-natural assay. We also exposed a social species (house finch Carpodacus mexicanus) to similar conditions. California towhees increased scanning rates when foraging with conspecifics, whereas house finches increased scanning rates when foraging solitarily. suggesting that vigilance in these species is regulated mostly through interference competition and through predation risk, respectively. California towhees did not show early detection, and actually the last detector in the group delayed detection in relation to solitary individuals. House finches benefited from early detection, but the second and last detectors maintained detection at the level of solitary individuals. California towhees increased the chances of fleeing when in groups in relation to solitary conditions, but this effect was less pronounced in the last detector. House finches always fled across conditions. Overall. an asocial avian species may use collective detection, but limited to certain types of cues: responses were more pronounced to overt (conspecifics walking or fleeing) rather than subtle (conspecifics becoming alert or crouching) social cues. (C) 2009 Published by Elsevier B.V.