Pronghorns (Antilocapra americana) are an important source of revenue and recreation for property managers throughout New Mexico, but have been declining in number. We documented body condition, survival, production of fawns, and trends in population size of pronghorns on the Corona Range and Livestock Research Center (CRLRC), a working research ranch and wildlife enterprise located in east-central New Mexico, from 2006 through 2011. Accrual of all indices of condition and size of both adult female and adult male pronghorns was positively associated with precipitation during June to July, August to September, and annually. Annual survival rates of females (0.33 to 0.78) and males (0.63 to 0.89) were highly variable on CRLRC. Survival of individuals was not related to any measure of condition or size taken the prior autumn. Survival of adult females was related to reproductive status the previous year; females that had successfully weaned >1 fawn the previous year were 0.11 times less likely to survive. Malnutrition was the most common cause of mortality (nine of 22 females; seven of 15 males), followed by suspected plant toxicities and enterotoxaemia (nine of 22 females) and harvest (six of 15 males). Most adult female mortality (73%) occurred after parturition and prior to weaning when energy demands are greatest on adult females; females that successfully weaned >1 fawn accrued significantly less condition by autumn. Survival of fawns was related to maternal condition, and fawn:adult female ratios were positively correlated with cumulative precipitation during late gestation and parturition. Low survival of adult females and fawns has resulted in the CRLRC pronghorn population declining from a minimum of 136 individuals to 66 from 2005 to 2011. Timing and causes of mortality highlight a strong nutritional limitation faced by lactating females related to the most energetic costs of reproduction being borne prior to the onset of summer monsoonal precipitation. The poor timing of reproduction to precipitation (and, thus, to forage phenology) in the southwestern United States will likely always limit productivity and survival of pronghorn relative to northern populations.
Bender, Louis C.; Boren, Jon C.; Halbritter, Heather; and Cox, Shad
"Factors influencing survival and productivity of pronghorn in a semiarid grass-woodland in east-central New Mexico,"
Human–Wildlife Interactions: Vol. 7
, Article 9.
Available at: http://digitalcommons.usu.edu/hwi/vol7/iss2/9