Because scavengers associate closely with predators, their vocalizations and movement behavior may signal imminent predation risk to prey. Moose in boreal forest ecosystems that face high predation risk have been shown to respond dramatically to this signal. In boreal forests, ravens associate closely with wolves, especially during wolf hunting forays. In these regions, the probability of survival, especially of young individuals, can often be as low as 30%. Research using playback calls of ravens has shown that moose in such high risk areas decrease their foraging rates and become increasingly vigilant by being watchful of imminent danger. This contrasts sharply with a lack of a behavioral response to playback of raven calls in geographic locations where wolves and other predators of moose have long been extirpated. In such areas, survival probability is at least three times higher than in the high risk areas. Differences in foraging rates between high and low risk areas are known to have differential effects on ecosystems because they lead to differences in the abundance of plant species that comprise the herbivore's forage.
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