TIMING OF PARTURITION AND LACTATION IN SOUTHERN MULE DEER

Factors related to timing of fawining in southern mule deer (Odocoileus hemionus fuliginatus) were studied in montane areas of San Diego Co., California, from June 1977 to January 1979. Mean date of birth was 27 June (SD = 7.4 days). Rates of nursing were highest in June and declined thereafter. Forage available to females following fawning was dry and of low quality; deer increased their consumption of browse during this period. A resultant shortened period of maternal care may have contributed to mortality (50-74%) of fawns. Timing of parturition may be related to the requirements of the maternal female during the last third of gestation when favorable temperatures and adequate precipitation combine to produce abundant forage. Sex ratios (males:females) changed markedly from yearlings (3.1:1) to adults (0.2:1), presumably because rutting activities followed harsh summer conditions.