Untying the knot: mechanistically understanding the interactions between social foragers and their prey

An entire flyway of shorebirds is dependent on the Dutch Wadden Sea. Here they find food to survive or fuel their flights towards the Arctic or Africa. Most shorebirds feed on worms and shellfish hiding in the mud. The work presented in this thesis concerns the foraging decisions of a socially foraging shorebird (red knot, Calidris canutus) feeding on shellfish such as small edible cockles (Cerastoderma edule). Questions we asked were: Does the spatial distribution of cockles predict the spatial distribution of knots? Do knots use each other to find food? Do individual knots have distinct ‘personalities’ regarding their foraging decisions? Knots varied in their search strategies, especially in the intensity of exploring novel environments. Measurements on individual exploratory tendencies in captivity correlated with this behaviour in the wild. After release, exploratory birds travelled to mudflats in England and Germany, whereas the non-exploratory birds remained in the Dutch Wadden Sea. To find the best food patches, knots exploited the searching efforts of their flock mates. Surprisingly, on the Wadden Sea mudflats, knots did not feed in patches with the highest densities of small cockles. Here, cockles competed for algal food and had low energy content.The work presented in this thesis offers a better understanding of spatial distributions of knots, but have wider relevance as well. For instance, contradicting the current viewpoint, our results show that prey density may be a poor predictor of energy intake rates. This has implications for predicting spatial distributions of predators, and estimating an area’s carrying capacity, i.e. the predator numbers that an area can sustain. The discovery of inter-individual differences in exploratory behaviour shows that individuals can cope differently with a rapidly changing world