Factors Affecting Neonatal Fawn Survival in Southern-Central Texas

Abstract

One hundred and twenty white-tailed deer (Odocoileus virginianus) fawns were captured in Lavaca and Gonzales Counties in 1971 through 1973. The fawns were 1 to 18 days of age and weighed 1.8 to 6.8 kg. They were observed during May and June in Lavaca County and June and July in Gonzales County. The mean home range of Lavaca County fawns was 32.5, 31.7, and 32.9 ha in 1971, 1972 and 1973, respectively. In Gonzales County, the mean home range was 34.3, 37.9, and 16.9 ha, respectively. Mortality rates were 25, 50, and 35 percent in Lavaca County, and 90, 35, and 10 percent in Gonzales County in 1971, 1972, and 1973 respectively; combined fawn loss was 47 percent. Predation accounted for 50 percent of mortality. Disease and starvation accounted for 34 percent. Sixteen percent of the deaths were undetermined. Significant correlations were noted between a declining deer population on poor range and fawn survival. Also, areas that were consistently overpopulated but had not suffered extreme droughts experienced moderate levels of fawn mortality each year. J. WILDL. MANAGE. 41(1):63-69 The purpose of this study was to determine the factors responsible for neonatal mortality of white-tailed deer in southerncentral Texas. Previous work by Brown (1964, 1965, 1967) indicated there were areas that consistently exhibited poor fawn production. Conception rates in 1964 and 1965 were 150 and 180 percent, but fall fawn crops varied from 50 percent in 1965 to 14 percent in 1967. This reduction indicated that substantial losses occurred between the late-spring fawning period and the fall census. Research on the Welder Wildlife Refuge, Sinton, Texas, revealed that high neonatal fawn mortality appeared to be the major factor stabilizing the deer herd (Cook et al. 1971:53). Cook et al. reported that up to 72 percent of radioequipped fawns were lost to disease, starvation, trauma, or predation. Teer et al. (1965: 49) noted that in the Llano Basin of Texas, 11 percent of the fawn production was lost shortly after birth. Screw-worm myiasis and starvation were suspected to be the causes of death. Predators were absent from the Llano Basin. Logan (1973:27) reported 18, 64, and 45 percent fawn losses during a 3year study on the Cookson Hills Deer Refuge in eastern Oklahoma. Lone star ticks (Amblyomma americanum) were associated with 71 percent of cases in which cause of death was determined. We acknowledge the field work conducted by D. H. Reid, D. E. Bujnoch, E. L. Stancik, M. W. Brown and Jack Adcock which included fawn capture and tracking; the assistance of Dr. R. M. Robinson of Texas AM radio electronics assistance provided by James Albert, the editorial assistance of D. E. Wilson; and the counsel, supervision and support of D. B. Frels throughout the course of this study.