How barn owls (Tyto alba) visually follow moving voles (Microtus socialis) before attacking them

The present study focused on the movements that owls perform before they swoop down on their prey. The working hypothesis was that owl head movements reflect the capacity to efficiently follow visually and auditory a moving prey. To test this hypothesis, five tame barn owls (Tyto alba) were each exposed 10 times to a live vole in a laboratory setting that enabled us to simultaneously record the behavior of both owl and vole. Bi-dimensional analysis of the horizontal and vertical projections of movements revealed that owl head movements increased in amplitude parallel to the vole's direction of movement (sideways or away from/toward the owl). However, the owls also performed relatively large repetitive horizontal head movements when the voles were progressing in any direction, suggesting that these movements were critical for the owl to accurately locate the prey, independent of prey behavior. From the pattern of head movements we conclude that owls orient toward the prospective clash point, and then return to the target itself (the vole) — a pattern that fits an interception rather than a tracking mode of following a moving target. The large horizontal component of head movement in following live prey may indicate that barn owls either have a horizontally narrow fovea or that these movements serve in forming a motion parallax along with preserving image acuity on a horizontally wide fovea.