High wind speeds decrease the responsiveness of birds to potentially threatening moving stimuli

Small foraging birds often rely on visual cues to detect the movement of potential threats. However, feeding in a high wind environment presents the challenge of interpreting the movements of many stimuli, most of which convey little information pertinent to survival. A bird that responds to each of these wind-driven movements would likely suffer the loss of much feeding time. Birds should thus become less responsive to moving stimuli at greater wind speeds. Furthermore, since inanimate objects should not move upwind, birds should generally be more responsive to upwind movements than typical downwind movements. By exposing passerine flocks to a moving, potentially threatening stimulus at various wind speeds, we found that these birds are in fact less responsive to stimulus movement (i.e. a lower tendency to flush to cover) as wind speed increases. However, birds were not more responsive to upwind movements of the stimulus. The propensity to flush was also not significantly affected by temperature or flock size. Responsiveness tended to decline over time, possibly indicating habituation to the stimulus, but the basic effect of wind speed held over the entire study. The general effect of wind on responsiveness suggests that the likelihood of responding to other stimuli or disturbances on windy days may also be reduced. (C) 2010 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.