CONICET | Buscador de Institutos y Recursos Humanos

The estuaries of the SW Atlantic region (from S Brazil to N Patagonia, Argentina) are stopover and wintering sites for several shorebird species that reproduce in North America and winter in South America (Morrison & Ross 1989). These environments are dominated by different crab species (Spivak et al. 1994). During studies carried out on estuaries in Argentina, seabirds and waterfowl have been observed consuming grapsid crabs in large numbers (Copello & Favero 2001, Berón 2003, Berón et al. 2007, García et al. 2008). However, shorebirds in the same environments have never been observed feeding on this type of prey, and their principal food items are polychaetes (Botto et al. 1998). The Greater Yellowlegs Tringa melanoleuca is a migratory shorebird that arrives in Argentina in the austral spring and remains until the austral autumn, when it returns to its breeding areas in North America. The literature shows that during the breeding season Greater Yellowlegs primarily eat small crustaceans, fish, worms and insects (Piersma 1996, Elphick & Tibbitts 1998). In Jan 2006, while carrying out an observation of this species foraging behavior along the estuary of the Quequén River, Buenos Aires Province, Argentina (38°35′S, 58°41′W), we observed three solitary Greater Yellowlegs feeding on crabs. The prey items they consumed (N = 11) were all identified as the grapsid crab Cyrtograpsus altimanus. The birds walked in the water until they saw a crab, then they captured it and first consumed the ambulatory legs and chelipeds and then the carapace until they had ingested it completely. We observed that Greater Yellowlegs could handle the crabs fairly quickly; but due to their size they could not be swallowed whole. Therefore, most of the handling time was spent pulling the crabs apart. After a crab had been swallowed, the bird would continue walking in the water searching for other prey. Two Greater Yellowlegs were also observed feeding on C. altimanus (N = 5) in the same area in Feb 2006.The little information that has been published on the feeding ecology of Greater Yellowlegs on the estuaries of Argentina indicates that they forage primarily on polychaetes in the lower intertidal zone (Botto et al. 1998). The observation of Greater Yellowlegs feeding on the grapsid crab C. altimanus has not previously been documented. However, crabs are part of the diet of other Tringa species, as shown by studies of Redshank T. totanus, Greenshank T. nebularia, and Spotted Redshank T. erythropus (van de Kam et al. 2004). Grapsid crabs are prey that have a high energy return (García et al. 2008). They are abundant in the area where Greater Yellowlegs feed on Argentinean estuaries and might be an important food item. Future investigations should examine their importance in the diet of the Greater Yellowlegs.

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