Does retinal configuration make the head and eyes of foveate birds move?

Abstract

Animals move their heads and eyes to compensate for movements of the body and background, search, fixate, and track objects visually. Avian saccadic head/eye movements have been shown to vary considerably between species. We tested the hypothesis that the configuration of the retina (i.e., changes in retinal ganglion cell density from the retinal periphery to the center of acute vision-fovea) would account for the inter-specific variation in avian head/eye movement behavior. We characterized retinal configuration, head movement rate, and degree of eye movement of 29 bird species with a single fovea, controlling for the effects of phylogenetic relatedness. First, we found the avian fovea is off the retinal center towards the dorso-temporal region of the retina. Second, species with a more pronounced rate of change in ganglion cell density across the retina generally showed a higher degree of eye movement and higher head movement rate likely because a smaller retinal area with relatively high visual acuity leads to greater need to move the head/eye to align this area that contains the fovea with objects of interest. Our findings have implications for anti-predator behavior, as many predator-prey interaction models assume that the sensory system of prey (and hence their behavior) varies little between species.

Spectral‐domain optical coherence tomography imaging of normal foveae: A pilot study in 17 diurnal birds of prey

“…Bird‐borne cameras have shown that when hunting, falcons orient their head in a position to keep the prey's image at visual angles consistent with use of their temporal fovea . Head and eye movements are also influenced by ganglion cell density across the retina . Birds with a more pronounced rate of change in ganglion cell density across the retina generally show a higher degree of eye movement and higher head movement rate.…”

“…Birds with a more pronounced rate of change in ganglion cell density across the retina generally show a higher degree of eye movement and higher head movement rate. This is likely attributed to the need for aligning the retinal areas of higher visual acuity with objects of interest . Additionally, head and eye movements are affected by the distribution of different types of cones in the retina.…”

“…40 Head and eye movements are also influenced by ganglion cell density across the retina. 41 Birds with a more pronounced rate of change in ganglion cell density across the retina generally show a higher degree of eye movement and higher head movement rate. This is likely attributed to the need for aligning the retinal areas of higher visual acuity with objects of interest.…”

“…This is likely attributed to the need for aligning the retinal areas of higher visual acuity with objects of interest. 41 Additionally, head and eye movements are affected by the distribution of different types of cones in the retina. Double cones are responsible for achromatic vision in birds.…”

Does Functional Lateralization in Birds Have any Implications for Their Welfare?

“…They suggested that the starlings' monocular alternating fixation strategy may facilitate integrating the different types of information gathered by the different portions of each retina. Various avian species are known to have different viewing strategies, depending on the distribution of cells in their retinas [105]. In chickens we know that close objects (20-30 cm in front) are viewed by using the binocular visual field and more distant objects are viewed by using the lateral, monocular visual field [106].…”