The differences between white-tailed and mule deer fawning habitat, and the effectiveness of thermal imagery for capturing deer fawns

There are 2 species in the genus Odocoileus found in North America. White-tailed deer (O. virginianus) are distributed across much of North America, while mule deer (O. hemionus) are restricted to the western third. The two species do occur sympatrically in 12 states including Texas. Previous research in Crockett County, Texas revealed that adults of each species partition habitat based on percent shrub cover, slope, elevation, and vegetation type and that adults of both species have high survival rates.

We focused on differences between mule deer and white-tailed deer fawn parturition dates, parturition sites, bed sites, and how bed site characteristics may affect survival. In order to increase our fawn sample we attempted to use thermal infrared imagery to detect and capture fawns. We discuss the limitations of thermal imagery on our study area.

We used univariate tests (i.e., Mann-Whitney U test and chi square goodness of fit test) to identify whether differences in birth site characteristics and parturition timing between mule deer and white-tailed deer were measurably different. We compared 7 models from parameters chosen a priori using AICC parameters estimates, SEs, and p-values to differentiate between fawn bed sites used by mule deer and white-tailed deer. We found a 33 day difference in median parturition date with white-tailed deer birthing before mule deer. Birth sites differed between species with white-tailed deer birthing at lower elevations on less steep slopes. White-tails also birthed in vegetation types associated with more mesquite and less juniper, while mule deer used more juniper vegetation types. Our best model based on AICC values (wi = 0.7061) contained 5 parameters: elevation, height of horizontal hiding cover, vegetation type, canopy plant species, and an interaction between canopy plant species and vegetation type to describe the differences between mule deer and white-tailed deer fawn bed sites. Additionally, we found that white-tailed deer fawns bedded farther from shrubs and on steeper slopes had better survival. There were no differences in bed site characteristics for mule deer fawns that survived or died.

We used thermal infrared imagery with little success in an attempt to capture greater number of fawns. After 59.5 person hours of mobile searching, we observed only one fawn, and captured none. We logged 24 hours of stationary observation and observed no fawns. The lack of a forest canopy may allow vegetation, mineral, and rock to heat excessively during the afternoon causing numerous "nonfawn hot spots" making detection of neonates difficult. Furthermore, the herbaceous vegetation on our site may have prevented the unit from detecting fawns. We recommend biologists assess on site characteristics and alternative uses for thermal imagery before purchasing this expensive equipment.