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We used naturally occurring spatial and temporal changes in prey abundance to investigate whether the foraging behavior of a social, territorial carnivore, the spotted hyena (Crocuta crocuta ), conformed to predictions derived from the ideal free distribution. We demonstrate that hyenas in the Ngorongoro Crater, Tanzania, redistributed themselves from less profitable to more profitable areas, even when this required them to undertake foraging trips to areas beyond their clan territory boundary, or required normally philopatric females to emigrate. As expected for a
system with rank related access to food resources in the territory, females of low social status foraged more often outside their territory and were more likely to emigrate than dominant females. Probably because Crater hyenas regularly foraged outside their territories, there was no correlation between clan size and prey density within territories, suggesting that clan sizes may have exceeded the carrying capacity of territories. A substantial decline of the hyena population in the Crater from 385 adults
in the mid 1960s to 117 in 1996 was most likely due to a substantial decline of their main prey. The decline in the hyena population was associated with a decline in the size of clans but not in the number of clans. The number of clans probably remained constant due to emigration by females from large clans into vacant areas or clans with
no adult females, and because hyenas regularly fed in areas containing concentrations of prey beyond their territory boundary. Between 1996 and 2003 annual recruitment rates of Crater hyenas consistently exceeded annual mortality rates, resulting in an almost doubling of the adult population. This increase was most likely due to an increase in prey abundance, a relatively low level of predation on hyenas by lions (Panthera leo), and an absence of high levels of disease related mortality.