Reproductive Performance of Female Key Deer

Abstract

The reproductive performance of the endangered Key deer (Odocoileus virginianus clavium) is a potential limiting factor in its conservation. We analyzed data collected by necropsy of 142 female Key deer from 1968 through 1989 to provide a better understanding of their reproduction. A breeding season of about 6 months was longer than for more northerly herds of white-tailed deer. Productivity of Key deer was low (0.76 fetuses/F -1 yr of age at breeding) and fetal sex ratio (74% M) was high for the species. Rates of reproductive activity (% pregnant or lactating) for females at age of breeding were 4% for fawns, 58% for yearlings, 61% for ages 2-4 years, and 90% for females -5 years of age. Eight (17%) of 48 pregnant females carried twins, and the remainder carried single fetuses. We hypothesize that poor reproductive performance of female Key deer is due to a nutrient deficiency or that it evolved as an adaptation to an insular habitat. J. WILDL. MANAGE. 55(3):386-390 The endangered Key deer of the lower Florida Keys are smallest in mass of the subspecies of North American white-tailed deer (Hardin et al. 1984) and are isolated from mainland Florida by 60 km of water. Prior to protection from hunting, the population of Key deer declined to a low of 25-80 in 1951-52 (Dickson 1955). Klimstra et al. (1978), using spotlight surveys, estimated that the population increased to 300-400 in the early 1970's. The U.S. Fish and Wildlife Service (1985) reported a decline in population to 250-300 by 1984. Low reproductive output apparently contributed to the slow recovery of the Key deer population from the low of the early 1950's (Hardin 1974). Currently, development encroaching on habitat (U.S. Fish Wildl. Serv. 1985) and mortality due to collisions with automobiles result in a precarious status for the Key deer population. Nutrition, one of the most important factors affecting productivity of white-tailed deer (Verme 1967, McCullough 1979), affects both ovulation rate and the proportion of females that become pregnant (Sadleir 1987). An imbalanced ratio of calcium (Ca) : phosphorus (P) or deficiencies of cobalt (Co), iron (Fe), or copper (Cu) probably contribute to low productivity of whitetailed deer from the southeastern United States (Smith et al. 1956, Harlow 1972, Smith and Hunter 1978). The diet of Key deer may be deficient in P (Widowski 1977) or other nutrients, forcing females <4 years old (that have not reached peak mass) to concentrate energy and nutrients on body growth rather than reproduction. We analyzed long-term data collected from mortalities of female Key deer to indirectly test this hypothesis. Numerous individuals of the National Key Deer Refuge and the Cooperative Wildlife Research Laboratory at Southern Illinois University, Carbondale contributed to the collection and examination of carcasses. We thank M. L. Folk, J. W. Hardin, J. L. Roseberry, T. G. Scott, T. J. Wilmers, and A. Woolf for reviewing a draft f the manuscript. The Key Deer Refuge pr vided use of computer facilities. This project was funded by a grant from the Richard King Mellon Foundation.