Possibility of Heat-Related Mortality in Desert Ungulates

Abstract

Studies on mortality of young ungulates in arid environments usually restrict the possible causes of death to predation, starvation, or disease. However, hyperthermia as a cause of death in wild animals living in arid environments is rarely discussed or considered and might be a source of mortality in juveniles. During a two-week period after 11 July 2005, four Sonoran pronghorn (Antilocapra americana sonoriensis) fawns (4–5 months old) died of unknown causes in a 130-ha enclosure in southern Arizona. Predation did not appear to be the cause of death. Likewise, starvation does not appear to be the cause of death because fawns did not exhibit observable signs of malnutrition prior to the period of their death. Disease also appears to be unlikely because the timing of occurrence of the vector for the two main diseases known to occur in the population (i.e., blue tongue and epizootic hemorrhagic disease [EHD]) does not coincide with the fawn deaths (although this does not rule out other potential disease). Hyperthermia might have been the cause of death of the four fawns because the three hottest days of the year (44.1, 44.1, and 43.6 °C) occurred during the period the fawns died. While our evidence for hyperthermia as the cause of death is speculative, biologists should consider the possibility that young desert-dwelling ungulates may be susceptible to hyperthermia during the hottest period of the year and that it might be a source of fawn mortality that cannot be managed.