Avian visual system configuration and behavioural response to object approach

Antipredator behaviour theory provides a framework to understand the mechanisms behind human–wildlife interactions; however, little is known about the role of visual systems in the responses to humans. We quantified responses of brown-headed cowbirds, Molothrus ater (Boddaert), and mourning doves, Zenaida macroura (Linnaeus), to object approach (a ground-based vehicle) and vehicle lighting regimen, and we examined two visual properties (visual acuity and visual fields) that could influence antipredator behaviour. Brown-headed cowbird groups exposed to vehicle approach and constant illumination of the vehicle-mounted lamp showed alert behaviour earlier than did groups exposed to pulsating treatments or no lamp. Interestingly, light treatments interacted with ambient light; cowbird alert response occurred sooner under sunny conditions and constant illumination of the lamp. Mourning doves were not affected by light treatments. Between species, mourning dove groups had a quicker alert response (and slower flight response) than brown-headed cowbirds. Visual acuity was higher and the visual field was wider in mourning doves than in brown-headed cowbirds. We speculate that brown-headed cowbirds might flush sooner to reduce predation risk costs associated with a relatively lower ability to visually track a given object. Our findings have theoretical and applied implications, as our model species belong to families that show different antipredator responses, and provide insight as to how object lighting might be used to reduce bird–structure/vehicle collisions, an increasing source of mortality in birds.