Ecology of sympatric mule deer and white-tailed deer in west-central Texas

Fluctuations in populations of sympatric mule deer (Odocoileus hemionus) and white-tailed deer (O. virginianus), as well as the potential for interspecific competition have fostered a need for information about the ecology of these unique populations to aid the development of management strategies. I estimated home range sizes, core area sizes, overlap, and survival of sympatric desert mule deer and white-tailed deer in west-central Texas. I captured 50 female mule deer, 53 female white-tailed deer, and 18 males of each species, fitted them with radio-collars, and monitored them for mortality from 2000 through 2003.

I calculated home ranges for 7 males of each species in 2001 and 2002. Home range sizes of male deer (mule deer, 8.8 km^; white-tailed deer, 7.4 km^) were similar. Interspecific home range overlap was less common than intraspecific overlap. Mean annual survival was 0.76 ± 0.04 (mean + SE) for mule deer and 0.80 ± 0.06 for white-tailed deer.

I estimated home range (95% kernel) and core area (50% kernel) sizes and overlap and survival of female deer. Average (+ SE) spring home range size of mule deer was 3.9 + 0.32 km"^ and white-tailed deer was 4.32 + 0.77 km^; summer home range sizes were 2.82 + 0.32 km^ and 2.08 + 0.23 km^, respectively. Interspecific seasonal home range overlap indices were similar to intraspecific overlap. Core area overlap also was similar within and between species during summer, but interspecific core area overlap was less common during spring. Mean (+ SE) annual survival of mule deer (0.91 + 0.08) was greater than survival of white-tailed deer ( 0.64 ± 0.10). Starvation and disease were the most commonly identified causes of death for males and females, suggesting improved quality and abundance of forage may be warranted to buffer environmental vagaries. However, significant spatial overlap indicated that tailoring management efforts to benefit just 1 species will require attention to the scale of intended activities.

I evaluated the role of vegetation community structure and topography on the habitat use of sympatric deer in west-central Texas using information obtained from radio-collared deer and a geographic information system (GIS). Both species used habitat in a non-random fashion and exhibited species- and sex-specific preferences. Mule deer used habitats with less vegetation cover and more topographic diversity, while white-tailed deer avoided landscapes at higher elevations. Males of both species avoided areas with greatest vegetation cover including those areas containing permanent water sources, but females tended to use such areas, particularly during summer fawning. Differences observed in the smaller core area scale were not always detected at the larger home range level, indicating that decisions about habitat use were made at different spatial scales.