Mortality by moonlight: predation risk and the snowshoe hare

Optimal behavior theory suggests that prey animals will reduceactivity during intermittent periods when elevated predationrisk outweighs the fitness benefits of activity. Specifically,the predation risk allocation hypothesis predicts that preyactivity should decrease dramatically at times of high predationrisk if there is high temporal variation in predation risk butshould remain relatively uniform when temporal variation inpredation risk is low. To test these predictions we examinedthe seasonably variable response of snowshoe hares to moonlightand predation risk. Unlike studies finding uniform avoidanceof moonlight in small mammals, we find that moonlight avoidanceis seasonal and corresponds to seasonal variation in moonlightintensity. We radio-collared 177 wild snowshoe hares to estimatepredation rates as a measure of risk and used movement distancesfrom a sample of those animals as a measure of activity. Inthe snowy season, 5-day periods around full moons had 2.5 timesmore predation than around new moons, but that ratio of theincreased predation rate was only 1.8 in the snow-free season.There was no significant increase in use of habitats with morehiding cover during full moons. Snowshoe hares' nightly movementdistances decreased during high-risk full-moon periods in thesnowy season but did not change according to moon phase in thesnow-free season. These results are consistent with the predationrisk allocation hypothesis.