Individual shifts toward safety explain age-related foraging distribution in a gregarious shorebird

Although age-related spatial segregation is ubiquitous, the underlying mechanisms are poorly understood. Here, we aim to elucidate the processes behind a previously established age-related foraging distribution of red knots (Calidris canutus canutus) in their main wintering area in West Africa (Banc d’Arguin, Mauritania). Based on 10 years of observations of 1232 uniquely color-ringed individuals of 1 to 18+ years old, we examined whether the observed age-related foraging distribution resulted from 1) spatial differences in mortality or 2) age-related shifts in habitat use. Using multistate capture–recapture modeling, we showed that with age foraging red knots moved away from the shoreline, that is, to areas with fewer surprise attacks by raptors. Considering uncertainties in the subjective gradient in predation danger with increasing distance from shore (as assessed from correlations between vigilance and distance from shore in foraging birds), we applied 2 different danger zone bounda...