Foraging ecology of the Great grebe Podicephorus major in Mar Chiquita lagoon (Buenos Aires, Argentina).

JOSENS ML, MS BÓ & M FAVERO

ARDEOLA

SOC ESPANOLA ORNITOLGIA

Año: 2010 vol. 57 p. 133 - 141

0570-7358

We studied the foraging ecology of the great grebe Podicephorus major through diet, prey energy return and foraging behaviour across three increasingly marine sites in the coastal lagoon of Mar Chiquita, Argentina. Grebes were followed by focal observations; we recorded dive duration, number of apparent successful and unsuccessful dives, size and type of captured prey and handling time above water.We analysed foraging effort as capture rate (i.e. number of prey eaten per minute) and capture success (i.e. number of successful dives per total dives made); and foraging efficiency as the number of captured prey per foraging time, the total biomass consumed and the energy intake obtained per time. We expected a piscivorous diet, but the most frequent prey were crabs, represented by Cyrtograpsus angulatus and Neohelice granulate, followed by diverse fish species. Diving time for different prey types and foraging sites did not differ. Handling time was higher for crabs. Foraging effort and foraging efficiency were higher for grebes that preyed on crabs, but in terms of biomass and energy return no differences were found, not even between sites. This suggests an opportunistic foraging behaviour for the great grebe in response to the possible higher availability of crabs in this and possibly other estuaries.