Factors Affecting the Number of Fetuses in a White-tailed Deer Herd

Data were taken on 1,103 pregnant white-tailed deer (Odocoileus virginianus) harvested from the Savannah River Plant in South Carolina from 1965-1985 to describe temporal, age specific, and habitat effects on fetal number. Time periods were thought to represent periods of high and low population density. Age was the most significant factor in altering fetal number both with and without the data from the fawns included. Low fetal numbers per doe in 0.5- and 1.5-year-old deer and a high incidence of twinning in the older deer was responsible for this effect. Mean number of fetuses per doe for the 0.5-year-old deer (x = 1.06) was less than for 1.5-(x = 1.56), 2.5- (x = 1.73), and ≥3.5- (x = 1.76) year-old age classes. Temporal and age specific effects among time periods on fetal number were significant in the analyses using data from all age classes. These effects were probably not related to density dependent feedback mechanisms, but rather to a sampling bias due to differential representation of deer of different ages or origin in the statistical analyses. Significant differences were observed in fetal numbers between females from the swamp and upland areas both with and without the data for the fawns. Differences between the densities, and/or habitat quality in the 2 areas were responsible for this effect.

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