Maximizing feeding efficiency and minimizing time exposed to predators: a trade-off in the black-capped chickadee

Abstract

Animals often must feed away from protective cover, sometimes at a considerable risk of being preyed upon. Feeding at the maximum rate while away from cover may simultaneously minimize the time spent exposed to predators, but this is not always the case. Under some circumstances, carrying prey items to protective cover before they are consumed will minimize the time spent exposed to predators, whereas feeding at maximum efficiency (staying to eat prey where they are found) will actually increase the time spent exposed to predators. Whether or not there is a conflict between maximizing foraging efficiency and minimizing exposure time, depends upon the travel time to cover relative to the handling time of a prey item; short handling times and/or long travel times are associated with the no-conflict situation, whereas the conflict situation is associated with long handling times and/or short travel times to cover. Free-ranging chickadees foraging at an artificial patch at various distances from cover can distinguish between these two foraging situations. When there is no conflict, they stay and eat at the patch. Their behavior in the conflict situation indicates that they are tradingoff foraging considerations against the risk of predation. When the cost of carrying is low and the benefit gained is high, the chickadees elect to carry items to cover; they tend to stay and eat at the patch when the relative magnitudes of costs and benefits are reversed.