Trophic ecology of Calidris alba and C. fuscicollis in Lagoa do Peixe, Rio Grande do Sul, Brazil

The family Scolopacidae includes cosmopolitan migratory waders, which congregate in numerous flocks in tropical coastal environments, used as stopping points for foraging. The Lagoa do Peixe National Park, in Rio Grande do Sul, is one of the most important stopping points for waders coming from the northern hemisphere that have Tierra del Fuego, Argentina, as their destination. The genus Calidris includes migratory birds that present an elastic ramphoteca and a sensible bill, and species of this genus generally feed on gastropods, bivalves, polychaetes, crustaceans and insects. Mixed-species foraging flocks of Calidris alba and C. fuscicollis are usually sighted in the Lagoa do Peixe region, and the analysis of the trophic niche of the two species suggests potential niche overlap or partition. Based on video footages made between February and March 2016 in the Lagoa do Peixe National Park and on ethograms built in BORIS software, we analysed C. alba and C. fuscicollis behavior, foraging area and foraging techniques. Preliminary results show that C. alba forages speedily following the waves, whilst C. fuscicollis is frequently sighted foraging far from the water. C. alba uses essentially random probes in the intertidal zone while C. fuscicollis employs non- random probes, showing interspecific dissimilarities in foraging. In the supralittoral zone, C. fusicicollis forages predominantly with long series of pecking, suggesting differences in the type of substrate or in the composition of macroinvertebrates between the intertidal and the supralittoral zones.