Changes in vigilance and foraging behaviour with light intensity and their effects on food intake and predator detection in house finches

Animals foraging in groups face different challenges, like avoiding predators and competing for food. One factor that has received little consideration is illuminance. Social animals exploiting sunlit patches could image the sun on their retinas, restraining visual perception, and, as a result, the use of personal and social information. Our goal was to assess the effects of illuminance under different levels of predation risk by studying pairwise interactions in house finches, Carpodacus mexicanus. We manipulated predation risk levels (low and high) and illuminance (low and high), and recorded changes in patch use, scanning and foraging behaviour, food intake rate, and predator detection. We found that illuminance affected the behaviour of house finches, which (a) avoided sunlit patches, (b) changed vigilance behaviour under high illuminance by reducing scan bout duration, (c) reduced foraging attempts under high light conditions, although food intake was not affected, and (d) increased the latency to detect a predator attack when foraging in pairs under high light conditions and when conspecifics showed antipredator responses that were more difficult to detect visually. If personal and social information sources about predation risk are restricted in sunlit patches, animals might increase their perceived predation risk. We discuss alternative interpretations, such as higher predation risk in sunlit patches due to greater visual exposure to predators. We suggest that heterogeneity in light conditions should be considered an ecological factor affecting foraging and antipredator behaviour in groups. (c) 2007 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.