Behavioral Ecology Advance Access originally published online on July 20, 2005
Behavioral Ecology 2005 16(5):938-944; doi:10.1093/beheco/ari074
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Mortality by moonlight: predation risk and the snowshoe hare
a Wildlife Biology Program, University of Montana, Missoula, MT, 59812, USA, and b Institut National Agronomique Paris-Grignon, 16 rue Claude Bernard, Paris, 75231, France
Address correspondence to P.C. Griffin. E-mail: paul.griffin{at}forestry.umt.edu.
Optimal behavior theory suggests that prey animals will reduce activity during intermittent periods when elevated predation risk outweighs the fitness benefits of activity. Specifically, the predation risk allocation hypothesis predicts that prey activity should decrease dramatically at times of high predation risk if there is high temporal variation in predation risk but should remain relatively uniform when temporal variation in predation risk is low. To test these predictions we examined the seasonably variable response of snowshoe hares to moonlight and predation risk. Unlike studies finding uniform avoidance of moonlight in small mammals, we find that moonlight avoidance is seasonal and corresponds to seasonal variation in moonlight intensity. We radio-collared 177 wild snowshoe hares to estimate predation rates as a measure of risk and used movement distances from a sample of those animals as a measure of activity. In the snowy season, 5-day periods around full moons had 2.5 times more predation than around new moons, but that ratio of the increased predation rate was only 1.8 in the snow-free season. There was no significant increase in use of habitats with more hiding cover during full moons. Snowshoe hares' nightly movement distances decreased during high-risk full-moon periods in the snowy season but did not change according to moon phase in the snow-free season. These results are consistent with the predation risk allocation hypothesis.
Key words: moonlight, moon phase, movement, predation rate, predation risk, prey behavior.