Comparative feeding ecology of shorebirds wintering at Banc d'Arguin, Mauritania

Limited knowledge of shorebird feeding ecology in the tropics hinders interpretation of considerable changes in numbers recently observed at the most important shorebird nonbreeding area along the East Atlantic Flyway, the Banc d'Arguin in Mauritania. We used droppings and video recordings to compare the diet and foraging behaviour of six shorebird species at Banc d'Arguin: dunlin, sanderling, red knot, ringed plover, grey plover and bar-tailed godwit. In four of those species, the detail achieved in prey identification allowed us to calculate niche width and foraging niche overlap. Sanderling and ringed plover consumed a wide range of macroinvertebrate taxa, while red knot consumed mainly bivalves with some gastropods, and both grey plover and bar-tailed godwit fed mainly on polychaete worms. A large proportion of dunlin droppings had no recognizable food items, suggesting a soft-bodied prey that we could not identify. Dunlin was the only strictly tactile forager, while sanderling and red knot used both visual and tactile methods. The remaining species resort to visual cues for catching prey, even though tactile cues may be important for bar-tailed godwits. Dunlin, sanderling, red knot and ringed plover all showed relatively narrow trophic niches and non-significant levels of foraging niche overlap. Overall, the diet of each shorebird was broadly similar to that reported from other parts of their wintering ranges, with more gastropods in the red knot diet than previously described. Our data suggest that the high shorebird densities at Banc d'Arguin despite low benthic food densities (Hydrobiologia 258:211-222, 1993a; Journal of Sea Research 60:235-243, 2008) may result partly from partitioning of available resources via narrow trophic niches with little overlap. Given these distinct trophic niches, the widespread declines in shorebird numbers at Banc d'Arguin may reflect changes in a wide range of prey types and suggest a shift in the overall properties of this unique ecosystem.