Lethal and nonlethal anthropogenic effects on spotted hyenas in the Masai Mara National Reserve

Abstract

We evaluated long-term patterns of human-caused mortality among free-living spotted hyenas (Crocuta crocuta) in a Kenyan game reserve and also assessed nonlethal anthropogenic effects on hyena behavior. We monitored naturally occurring vigilance in 2 clans of hyenas, 1 disturbed and the other undisturbed. The disturbed clan, living on the edge of the reserve, experienced much human disturbance from both tour vehicles and livestock grazing, whereas the undisturbed clan, living in the center of the reserve, also experienced tour vehicles but no livestock grazing. The proportion of all deaths with known causes that could be attributed to humans increased between 1988 and 2006 in the disturbed population; humans caused no mortality in the undisturbed population. Disturbed hyenas were more than twice as vigilant when resting, and they nursed their young closer to bushes, than undisturbed hyenas. Disturbed hyenas also were most vigilant on days when livestock were present in their territory, but we observed no effects of tourism on hyena vigilance. We next conducted playback experiments in which we used cowbells as treatment sounds and church bells as control sounds to determine whether hyenas from the 2 clans responded differently. After hearing cowbells, disturbed hyenas increased their vigilance more than did undisturbed hyenas. However, disturbed hyenas also increased their vigilance after hearing church bells, suggesting that disturbed hyenas may exhibit heightened responsiveness to a wide array of anthropogenic sound stimuli. Our findings suggest that human activities related to pastoralism are having measurable effects on hyena mortality, and that hyenas appear to be responding to this threat by modifying their behavior.