Social shorebirds forage together, but it looks as though, as the size of the flock increases, anticipating the actions of others infringes on their hunting of delicious little molluscs.
Bijleveld and co (from the University of Groningen and the Royal Netherlands Institute for Sea Research) used five focal birds, teaming them with large and small groups of dominant or subordinate birds, to assess how they spent their precious foraging time as the number of their competitors or the density of the food (blue mussels) changed. The authors discuss how, as group size increased, birds spent more time watching other birds, possibly to avoid aggressive encounters. Changing direction to avoid collisions could also have meant that birds covered the same patches twice, rather than searching through the sand efficiently. There’s not much discussion of the idea that the watching could have been unsuccessful foragers trying to gain information from the successful ones (i.e. 10 habits of highly successful shorebirds) but the feeding patch was small, constantly moving and the food resource patchy so additional information might not be a concern.
I love the tide mimic they dreamt up, where a moving sheet covers all but a small food patch, but I don’t envy them the task of measuring those hundreds of mussels.
Full paper details and abstract here for ‘Experimental evidence for cryptic interference among socially foraging shorebirds’.
For those with access, there’s a great video in the Supplementary info.
Update: Four, not five, birds were used in the analysis. Hopefully this will be followed by larger studies.