The influence of distance to burrow on flight initiation distance in the woodchuck, Marmota monax

Abstract

We used woodchuck (Marmota monax) to test predictions of a cost-benefit of antipredator behavior that flight initiation distance would increase with distance to refuge and predator approach velocity. We also examined the effects of distance to refuge and predator approach velocity on escape velocity and on both temporal and spatial margin of safety (expected time distance between predator and burrow at the time of the woodchuck's arrival). The observer assumed to be perceived as potential predator, approach juvenile woodchucks from the direction to the burrow at a slow (1.24 m/s) or fast (1.79 m/s) walking pace. When the woodchuck started to flee, the observer recorded the woodchuck's distance from the observer and from its burrow, the time spent running, and whether the woodchuck stopped before reaching its burrow. Flight initiation distance increased consistently with distance to the burrow over the entire observed range (0-25 m) but was not significantly affected by observer approach velocity. Escape velocity was not significantly influenced by the observer approach velocity and was approximately constant over the range of 2-25 m, but was slower for woodchucks less than 2 m from their burrow. Both temporal and spatial margins of safety increased with distance from the burrow. The temporal margin of safety increased with distance from the burrow more rapidly for slow fast observer approach velocity. Woodchucks fleeing from greater than 2 m usually stopped near the burrow before entering, but those from closer distance usually entered directly. The result support the assumption that antipredator behavior is sensitive to the costs and benefits of alternative escape decisions.