Food preferences and social behaviour differ among cultures worldwide, not only in humans. This thesis describes studies of the behaviour of red knots, shorebirds that winter on the subtropical intertidal mudflats of Banc d’Arguin in Mauritania. By comparing them with red knots in the Dutch Wadden Sea, we show that their choices are the consequence of their environment: and that causes enormous differences.Red knots spread across the mudflats at low tide, poking the sediment with their bill in search of bivalves. They swallow them whole, and crush them in their muscular stomach, the gizzard. With experiments, we show that whereas Dutch red knots choose the prey that is easiest to digest, Mauritanian red knots actively choose a varied diet. They are careful not to eat too much Loripes lucinalis, the most abundant bivalve there, which contains sulfide and causes diarrhea. Ignoring Loripes is not an option for red knots, because other prey are much harder to digest. But the proportion of Loripes in the diet differs greatly between red knots, and that correlates with their gizzard size. Interestingly, gizzard size is the consequence of diet choice, rather than vice versa. These and many more choices depend on the environment. For example, we showed that red knots at Banc d’Arguin are more individualistic, and show much stronger site fidelity, because the food there is much more spread out across the landscape. This research stresses the potential importance of experiences and learning on red knot behaviour. That knowledge is important, because these dependencies on the environment greatly change the expected consequences of environmental change on ecosystems.
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