SMALL MAMMAL RADIOECOLOGY: NATURAL REPRODUCTIVE PATTERNS OF SEVEN SPECIES

摘要

To provide basic information required to interpret subsequent radiation studies, autopsy results pertinent to litter size and reproductive season of 7 small-mammal species are presented. The data are from about 6400 individuals captured at Pinawa, Manitoba during a 6 year trapping period (1967-1972). The normal breeding season for Peromyscus maniculatus, Clethrionomys gapperi Micvotus pennsylvanicus, Sorex cinereus and Sovex arcticus extended from April through September. The breeding season of Blarina brevicauda was shorter, with conception and birth occurring in the May-August period. The hibernator, Zapus hudsonius, had the shortest breeding season, with conception and birth apparently limited to June and July. Young Z. hudsonius, S. arcticus and B. brevicauda did not appear in the traps until July, but young of the other species were captured in June. It is probable that young of all species except Z. hudsonius and B. brevicauda breed in the summer of their birth. Embryo counts in pregnant adult females varied from a low of 5.6 for M. pennsylvanicus to a high of 6.8 for S. cinereus . In all species, young-of-the-year females had lower embryo counts and resorbed more embryos than adult females. Testis position and length, and presence of sperm in the epididymis, were the parameters used as indicators of reproductive capacity of the males. A combination of testis length and presence of sperm may be the most accurate indicator of reproductive potential on an annual basis. Sex ratios, percentages of young in the population, and body weights of the sex and age classes are tabulated on monthly basis for each species.