Behavior and the Reproductive Cycle in the Cottontail

Observations of behavior during all phases of the reproductive cycle were made on a small population of individually marked cottontails (Sylvilagus floridanus) confined in a large field enclosure. The peak period of social activity was found to be between 6 and 8 PM, and the onset of evening activity did not vary with increasing day length. Nine basic types of adult social interactions are described. Evidence is presented for a synchronized first, and six subsequent, breeding periods. A 7-day behavioral rhythm is present during the onset of breeding and the first pregnancy but is apparently absent following postpartum periods, possibly as a result of behavioral changes in the nursing females. The onset of reproductive activity was February 14-15, and by August 15 the population showed reproductive regression. The study population was closely synchronized with the natural population surrounding the enclosures. Brief periods of severe weather reduced reproductive activity markedly, and a brief period of snow cover probably delayed the onset of breeding. The series of events during the postpartum estrous period is described. This series, from final nest preparation through birth and mating to an unreceptive condition of the female, lasts less than 2 hours. Six pregnancies were timed and the gestation periods were between 26 and 28 days.