Age at First Conception in Black-tailed Deer

Abstract

Under captive conditions, some 50% of female black-tailed deer (Odocoileus hemionus columbianus) fawns conceive in their first year. Wild fawns first conceive in their second year of life. The growth of wild and captive fawns was similar until mid-October. Wild fawns then ceased to grow. Captive fawns that subsequently gave birth in June grew faster than captive fawns that did not reproduce. During the breeding season of November-December the range of body weights of samples of wild fawns, of captive fawns which bred and of captive fawns that did not breed, all overlapped. It is suggested that the timing of puberty is regulated by photoperiodic influences and that fawns can first conceive when they reach their individual critical body weight if nutrition is adequate.