The role of parasites, diseases, mineral levels, and low fawn survival in a declining pronghorn population in the Trans-Pecos region of Texas

Since the late 1980s, pronghorn populations of west Texas have been in a steady decline. Texas Parks and Wildlife Department's (TPWD) 2012 surveys showed that the population was estimated at 2,751 animals, a 75-year low for the region. In 2009, a study was initiated to determine some of the leading causes for the recent decline in this region, including prevalence of diseases, mineral concentrations, parasites, and fawn survival. I found an average prevalence of titers for blue tongue virus (BTV) to be 97% and 92% for epizootic hemorrhagic disease (EHD) in 2010 and 2011, respectively. Because trace mineral levels (e.g., copper and selenium) have also been tied to productivity in pronghorn, I compared mineral levels between the Trans-Pecos and Panhandle. Copper serum levels were the same between regions ( P = 0.199), but copper liver levels (P = 0.002), and selenium levels were different (P < 0.001). I also investigated the roles of parasites and predation as a limiting factor for pronghorn production in the Trans-Pecos. I found a difference when comparing Haemonchus worm counts (P = 0.041) and fecal egg counts (P < 0.001) between regions (Trans-Pecos, Panhandle). In 2011, surveys showed some areas to have fawn crops as low as 0% (0 fawns: 100 does), with a Trans-Pecos average at 10%. In 2012, TPWD surveys indicated that the fawn crops averaged about 16% Trans-Pecos wide. I conducted a pronghorn fawn survival study to determine major causes of mortality. Predation was the major cause of mortality in both 2011 and 2012. Bobcat (Lynx rufus ) predation accounted for 32%, unknown predation accounted for 28%, and coyote (Canis latrans) predation accounted for 24% of all mortalities. Marginal mineral levels, high Haemonchus loads, and high predation on pronghorn fawns appear to be having a negative impact on pronghorn populations in the Trans-Pecos.