Onset and cessation of activity in cottontail rabbits and snowshoe hares in relation to sunset and sunrise

Abstract

Summary Onset and cessation of activity were studied in cottontail rabbits (Sylvilagus floridanus) and snowshoe hares (Lepus americanus) through the use of an automatic radio-tracking system. These times varied greatly for the male cottontails studied in January but were more consistently correlated with sunrise-sunset times for the females in February. Contradictory conclusions of other workers are examined, and possible reasons for the contradictions given. Onset and cessation of activity in a female snowshoe hare studied in late winter and spring closely followed sunrise-sunset times, and there was a high correlation (r=0·95) between seasonal changes in periods of daily inactivity and seasonal changes in length of daylight. Data suggest that cessation of activity may be stimulated by a certain light intensity rather than actual sunrise.