Onset of Evening Activity of Swamp Rabbits and Cottontails in Relation to Sunset

Onset of evening activity was recorded for ten swamp rabbits (Sylvilagus aquaticus) (1967 breeding season) and 22 cottontails (S. floridanus) (1960-1962 breeding seasons) confined in 1.8-2-acre enclosures. As sunset was delayed toward spring, the onset of activity of individual swamp rabbits was delayed. The delay was greater for females and the lowest-ranking male than for the reproductively active males. The still later sunsets of late spring and summer were not accompanied by a further delay in onset of evening activity, and time of onset became highly variable but occurred well before sunset. Cottontail data indicated a pattern similar to that of swamp rabbits. Onset of activity for both species occurred during the twilight period following sunset in late winter and early spring but well before sunset in late spring and summer.