Abstract
Barn owls, like primates, have frontally oriented eyes, which allow for a large binocular overlap. While owls have similar binocular vision and visual-search strategies as primates, it is less clear whether reflexive visual behavior also resembles that of primates or is more similar to that of closer related, but lateral-eyed bird species. Test cases are visual responses driven by wide-field movement: the optokinetic, optocollic, and optomotor responses, mediated by eye, head and body movements, respectively. Adult primates have a so-called symmetric horizontal response: they show the same following behavior, if the stimulus, presented to one eye only, moves in the nasal-to-temporal direction or in the temporal-to-nasal direction. By contrast, lateral-eyed birds have an asymmetric response, responding better to temporal-to-nasal movement than to nasal-to-temporal movement. We show here that the horizontal optocollic response of adult barn owls is less asymmetric than that in the chicken for all velocities tested. Moreover, the response is symmetric for low velocities (< 20 deg/s), and similar to that of primates. The response becomes moderately asymmetric for middle-range velocities (20–40 deg/s). A definitive statement for the complex situation for higher velocities (> 40 deg/s) is not possible.
Highlights
Birds and mammals share a similar anatomical forebrain organization (Stacho et al 2020)
Symmetry or asymmetry of the reflexes occurs under monocular stimulation, when nasal to temporal (N–T) and temporal to nasal (T–N) directions of movement may be discriminated
Barn owls are able to actively rotate their head by more than 270° (Krings et al 2017), we typically observed a range of ± 50° during the slow-phase movements, with some extreme head rotations beyond 100° (Fig. 3)
Summary
Birds and mammals share a similar anatomical forebrain organization (Stacho et al 2020). Owls represent an interesting case as their frontally oriented eyes create a large binocular overlap that allows the owls to extract depth by stereo vision (Willigen et al 1998, 2002, 2003). These birds have a well-developed scleral ring that stabilizes the eyes in the skull (Franz-Odendaal and Krings 2019). Owls exhibit OCRs to stimulation with visual wide-field patterns This is similar to the other birds mentioned before. Most other bird species as well as e.g. frogs, turtles and many mammals have laterally-positioned eyes, and exhibit so-called asymmetric OKRs or OCRs, while primates have frontally-positioned eyes and have a symmetric horizontal OKR. The question arises whether the OCRs of owls more closely resemble those of their avian relatives or of primates with their similar visual world
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