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Citation. Mech, L. D.; Heezen, K. L.; Siniff, D. B. 1966. Onset and cessation of activity in cottontail rabbits and snowshoe hares in relation to sunset and sunrise. Animal Behaviour 14(616):410-413.   [1433  CC]

Abstract. The study of environmental cues that trigger the onset and cessation of activity is an important area of research in circadian rhythms, and much work has been done by altering light/ dark regimes of captive animals and noting the effect of activity. Few studies, however, have been conducted on activity cycles of animals in the wild. DeCoursey's 1959 investigation of a wild population of Glaucomys volans, and her study of a captive population (DeCoursey, 1960) demonstrated a close parallel between sunset and beginning of activity. It seems reasonable that the stimulus for the onset of activity in most nocturnal species, or perhaps their entrainment cue (Bruce, 1960), is decreasing light intensity, but some studies have indicated that no such relationships exist. Lord (1961) using roadside censuses to study cottontail rabbits (Sylvilagus floridanus) concluded that 'some factor is overriding the "sunset factor" as the stimulus for onset of activity....' He later studied the activity of penned cottontails and drew the same conclusions (Lord, 1964). The present investigation of four wild cottontail rabbits and five snowshoe hares (Lepus americanus) during late winter and spring examines the variation in length of the circadian cycle among individuals and days and compares the onset and cessation of activity with sunset and sunrise times.

Keywords. Lagomorpha, circadian rhythms

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