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-benef it model of antipredator behavior that flight initiation distance woul d increase with distance to refuge and with predator approach velocity . We also examined the effects of distance to refuge and predator appr oach velocity on escape velocity and on both temporal and spatial marg in of safety (expected time and distance between predator and burrow a t the time of the woodchuck's arrival). The observer, assumed to be pe rceived as a potential predator, approached juvenile woodchucks from t he 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 r ecorded the woodchuck's distance from the observer and from its burrow , the time spent running, and whether the woodchuck stopped before rea ching its burrow. Flight initiation distance increased consistently wi th distance to the burrow over the entire observed range (0-25 m) but was not significantly affected by observer approach velocity. Escape v elocity was not significantly influenced by the observer approach velo city 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 burro w more rapidly for slow than for fast observer approach velocity. Wood chucks fleeing from greater than 2 m usually stopped near the burrow b efore entering, but those from closer distances usually entered direct ly. These results support the assumption that antipredator behavior is sensitive to the costs and benefits of alternative escape decisions.