Patterns in Twelve Reproductive Parameters for the White-Footed Mouse (Peromyscus leucopus)

Abstract

Four male and eight female fecundity criteria were statistically analyzed for 343 white-footed mice (Peromyscus leucopus) from Monongalia County, West Virginia, to ascertain the duration of the breeding season, peak breeding time, and the seasonal reproductive changes among both sexes in the wild population. From May 1969 through May 1970, the breeding season extended from February through October. Two periods of intensified breed occurred, one in the early spring and one in the late summer. Between the spring and summer breeding periods, male breeding activity decreased and reached a low in June, which was similar to but shorter in duration than the period of low fertility that occurred from October through January. All four parameters examined in males showed virtually identical patterns of change. Peak pregnancies were recorded in April-May and during August. Patterns similar to that of pregnancy were observed in seven of the eight female parameters analyzed, and the reproductive activity of the females was essentially identical to that of males. Breeding activity also decreased in June for females. Both sexes began reproductive activity in February. There was no evidence that the females become reproductively active earlier or later than the males. The decline in breeding activity in June was probably associated with age structure, because of the relationship of testes size to body weight in the May–June “season,” the general decline in body weight in June for both sexes to the low point of the year, and possibly low corpora lutea and implantation counts in June. There was probably no decline in individual reproductive performance per se but young adults entering the population diluted the number of reproducing adults already present.