Variation in Conception Dates in Black-Tailed Deer in Western Washington

Abstract

The season of birth in deer in temperate climates is generally considered to coincide with the most favorable period of the year for survival of the fawns. The dates in conception in black-tailed deer (Odocoileus hemionus columbianus), calculated from embryos collected during the hunting season were studied in two populations from 1980 to 1988. Substantial variations between years were noted in one of the populations. Four potential factors have been postulated as possible causes of this annual variation: (1) disturbance due to hunting during the breeding season; (2) changes in female age structure; (3) availability of sexually mature males for breeding; and (4) variations in physiological condition of does. The first three factors have been rejected as possible causes of the dramatic shifts noted. The fourth factor, influenced by annual changes in climatic conditions and hence forage productivity, is the subject for continued research.