Weather Influences on the Onset of Breeding in Missouri Cottontails

The purpose of this paper is to report the effect on breeding in Missouri cottontails of a period of abnormally high snowfall and prolonged cold in February and March of 1960. In most years, central Missouri cottontails (Sylvilagus floridanus) begin breeding about the end of February. Schwartz's (1942) data for 1939 and 1940 showed first conception dates about March 1, and our own data for 1958 and 1959 show a median first conception date of February 26. The uniformity of the onset of breeding in these 4 years suggests a photoperiod effect governing the onset of breeding. Lyman (1943) demonstrated that altering the duration of illumination may modify greatly both the sexual and molting cycle in the varying hare. Bissonette (1938) and Bisson