Birth Synchrony and Survival of Pronghorn Fawns

Predation is often the primary mortality factor of neonatal pronghorn (Antilocapra americana). Birth synchrony can affect predation rates of young for some ungulates, but has not been examined in pronghorn. We investigated causes of mortality and the effect of birth synchrony on survival of neonatal pronghorn (n = 104) at Hart Mountain National Antelope Refuge in southcentral Oregon from mid-May to mid-July in 1996 and 1997. Most (84%) of the marked fawns died during the monitoring period. Average age at death was 8.4 days and 83 (95%) of the fawns that died were < 18 days old. Predation, primarily coyote (Canis latrans), accounted for 86% (75/87) of the fawn deaths. Birth date affected survival where neonates born during the peak period of fawn drop lived longer than those born during the non-peak period (P ≤ 0.002). Of 17 surviving fawns, 14 had birth dates during the peak fawning period compared to 3 born during the non peak period (P = 0.024). Survival rates for all fawns born during the peak fawning period (S 60 = 0.23) were greater (P < 0.001) than fawns born during the non-peak period (S 60 = 0.07). Our results indicated that birth synchrony in pronghorn may be an important adaptation through which losses of young to predation can be reduced.

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