Visual specialization of an herbivore prey species, the white-tailed deer

Abstract

To gain knowledge of visual specializations influencing the behavior of white-tailed deer ( Odocoileus virginianus (Zimmermann, 1780)), we examined gross eye characteristics, structural organization of the retina, and the density and distribution of cone photoreceptors. White-tailed deer possess ocular features similar to other ungulates including a horizontal slit pupil, reflective tapetum lucidum, typical retinal structure, and medium wavelength sensitive cone photoreceptors concentrated in a horizontal visual streak. The tapetum was found to cover the superior portion of the eye and overlapped the horizontal visual streak. Comparisons between fawns and adults did not reveal any differences in retinal thickness, retinal nuclei counts, or cone photoreceptor counts. While M-cones had increased density in the visual streak, S-cones were distributed evenly across the entire retina. Schematic eye calculations of a 0.5-year-old deer indicated a hyperopic eye (+7.96) with a F/# ranging from 5.55 to 1.39 for pupil diameters of 3 to 12 mm. As expected for a crepuscularly active prey species, the visual system of white-tailed deer is specialized for sensitivity in low-light conditions and detection of predators.