Seasonal variation in sex ratios and survival rates of white-tailed deer fawns
Type of DegreeThesis
DepartmentForestry and Wildlife Sciences
MetadataShow full item record
The ability of a female to adjust the sex ratio of her offspring has been well documented in numerous mammalian species. However, few studies have deviated from focusing on maternal condition as the driving factor concerning sex ratio variation. In this study, we investigated how birth date influenced offspring sex ratios in a captive herd of white-tailed deer (Odocoileus virginianus) located in Michigan. Since it has been predicted that females will bias the sex ratio of her offspring in order to increase her lifetime fitness, we hypothesized that more males should be born earlier in the birthing season. Offspring born earlier will have more time for development and therefore have a greater potential for increased dominance and body size later in life, traits related to male reproductive success. In this study, we found that maternal condition did not influence offspring sex ratios, while birth date did. It was found that more males tended to be born during the second and fourth birthing periods, with females dominating the first, third and fifth birthing period. In addition, the mass of male fawns at six months decreased with later birthing dates, a trend not as apparent in female fawns. This suggests that by varying offspring sex ratios, a female can improve her lifetime fitness by investing in the sex that will gain the greatest reproductive advantage by being born at certain times. As humans continue to move from the urban epicenter, management of wildlife in these areas is becoming increasingly important. However, since wildlife residing in these areas are exposed to different stresses than their rural counterparts, they may exhibit behavioral or life history modifications, ultimately decreasing the effectiveness of management decisions. One life history characteristic that is important to understand before implementing management decisions is survival. In white-tailed deer, a great deal of natural mortality occurs within the first few months of life, and therefore has the potential to greatly influence population dynamics and management decisions. In this study, we determined the cause, timing, and factors influencing neonatal mortality of a suburban population of white-tailed deer in Alabama. We found a 67% mortality rate, with the leading causes of mortality being predation by coyotes (41.7%) and starvation due to abandonment (25%). We also found that survival rates were different between the two years of the study (23.5% in 2004 and 42.1% in 2005; with fawns born in 2005 being 1.49 more likely to survive than fawns born in 2004), were linearly related to time following birth (survival increasing by 1.36 with each additional week after birth), and were positively associated with mass at birth (survival increasing by 1.69 with each additional kg of birth mass). These mortality rates are greater than most rural populations, suggesting that population growth rates of white-tailed deer found in suburban areas may be limited by increased mortality rates early in life.