Influences of Light on Activity and Phasing of Carnivores

Abstract

Influences of light on the locomotor activity and phasing of 42 carnivores from 16 species were studied on four light regimes employing natural or artificial twilights: (1) outdoor light; (2) indoor, 24-h artificial light cycles with unvarying day and night illuminance and stepwise illuminance changes every 30 min during activity; and (3) indoor 3- or 4-h cycles. Responses to such tests may be the best available behavioral guide for assessing the overall state of adaptation of the visual system. Genets, kinkajous, and ringtails were strongly nocturnal. The behavior of kit foxes, long-tailed weasels, and red foxes suggests visual systems best adapted for dim light but also suitable for daylight. The arctic fox, gray fox, and striped skunk appear to be adapted for both day and night vision. Behavior of a juvenile coyote suggests optimal vision in twilights and moderate daylight, while that of a juvenile red wolf suggests better vision in moderate daylight than dim light. Animals that appear to be adapted best for daylight vision included mongooses, coatis, tayras, and a grison, but the latter three also appear to be well suited for dim-light vision. The coyote, gray foxes, long-tailed weasels, two of the three mongooses, and the red wolf were markedly or completely inhibited in darkness; those uninhibited or only partially inhibited included coatis, genets, kinkajous, kit foxes, ringtails, and a striped skunk. Large differences in individual responses to illuminance alternations and 3- or 4-h light cycles are probably characteristic of species with great versatility of vision. But the highly consistent responses of some individuals in some tests show that even animals with highly versatile vision may respond in stereotyped ways to changes in ambient illuminance. The activity distributions of certain individuals were sometimes influenced by time of feeding, while the phasing of one long-tailed weasel depended entirely on feeding time. About one-third of the animals "warmed up" to maximum speed after rest periods. Comparisons of the outdoor and indoor results suggest that the artificial, indoor 24-h light cycle with simulated twilights is a good substitute for the natural-light regime.