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

We used woodchucks (Marmota monax) to test predictions of a cost-benefit model of antipredator behavior that flight initiation distance would increase with distance to refuge and with 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 and distance between predator and burrow at the time of the woodchuck's arrival). The observer, assumed to be perceived as a potential predator, approached juvenile woodchucks from the direction opposite 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 burrows. Both temporal and spatial margins of safety increased with distance fr om the burrow. The temporal margin of safety increased with distance from the burrow more rapidly for slow than for fast observer approach velocity. Woodchucks fleeing from greater than 2 m usually stopped near the burrow before entering, but those from closer distances usually entered directly. These results support the assumption that antipredator behavior is sensitive to the costs and benefits of alternative escape decisions.