Danger management and the seasonal adjustment of migratory speed by sandpipers

Abstract

The behavior of migrating birds is governed by time‐, energy‐ and danger‐minimizing strategies. The adjustment of migration speed (i.e. the rate at which distance is covered during a migration) is a behavioral tactic that might contribute to these strategic goals. Shorter stopovers and greater fuel loads increase migration speed, but both require more intensive foraging at stopovers, making migrants more vulnerable to predators. A simple numerical model shows how seasonal alterations in migration speed can lower the exposure of western sandpipers to peregrine falcons, their most important predator. The ‘caution–speed–caution’ pattern of higher migration speed in the mid‐passage period, observed in earlier work, requires that the intensive foraging necessary heightens vulnerability, and that migrants are exposed to both migrant predators as well as predators resident at migratory stopovers.