The influence of the predator landscape on migratory decisions in two shorebird species

I tested predictions about foraging decisions and stopover durations based on a mortality-minimizing migratory model in two shorebird species on southward migration. Semipalmated and adult western sandpipers migrate early, under low predation danger and are predicted to make behavioural decisions that allow them to avoid exposure to the seasonal increase in abundance of their main predator, peregrine falcons. Juvenile western sandpipers migrate later, experiencing higher predation danger. They are predicted to make decisions that reduce vulnerability to falcons. Early migrants seasonally lowered vigilance and adjusted stopover duration, increasing migratory speed to remain ahead of the approaching migratory falcons. Late migrants had higher vigilance, and stopover duration trends fitting reduced vulnerability at the expense of migratory speed. Flight initiation distance and spatial usage were not consistent with predictions. These species appear to make decisions that depend on spatial and temporal proximity to predator migrations, as predicted by a mortality-minimizing migration model.