Human disturbance of breeding Wood Sandpipers Tringa glareola: implications for "alert distances" in prescribing protective buffer zones

Abstract

Separation of animals and humans using a protective set-back distance (Minimum Ap-proaching Distance) is a popular tool for conservation managers to promote wildlife-hu-man coexistence. In several cases, Minimum Approaching Distance is based on how ani-mals respond to an approaching human, using Flight Initiation Distance or Alert Distance. Alert Distance, when animals first show increased vigilance to an approaching human, is considered the best basis for Minimum Approaching Distance because animals have time to adapt their response. Alert Distance is frequently difficult or impossible to measure in practice, however, especially in breeding birds. Using a study of breeding Wood Sandpip-ers Tringa glareola, in which Alert Distance could not be measured directly, we tested three possible solutions to this dilemma. Alarm Call Distance did not appear to provide a useful substitute for Alert Distance because sandpipers probably alarm called after they had first detected a human. Published predictions of Alert Distance using body mass also failed to provide realistic estimates of disturbance distances in Wood Sandpipers. The "fixed-slope rule", which predicts that Alert Distance is about double Flight Initiation Distance, was not supported by relationships between Alarm Call Distance and Flight Ini-tiation Distance, but was supported by a relationship between an estimated Alert Distance surrogate and Flight Initiation Distance. This suggests that this rule may have general util-ity in predicting Alert Distance when only the more readily measured Flight Initiation Distance metric is known. A Minimum Approaching Distance (protective buffer zone) of 160 m is recommended for breeding Wood Sandpipers.