Changes in Patterns of Wetland Utilization by the Red Knot, Calidris canutus rufa, in Península Valdés: A Need or an Approximation to the Optimum.

BALA, L. O.; V. L. D'AMICO; M. A. HERNÁNDEZ

Virginia, USA

Congreso; Wader Study Group. Special Spring 2001 Meeting, Wallops Marine Consortium,; 2001

Red Knot Calidris canutus rufa use Fracasso beach (San José Gulf, P. Valdés, Argentina) as a regular stop in their migration from Tierra del Fuego to Canadian Arctic. In this wetland, they feed on intertidal invertebrates. Therefore their access to the trophic resource depends on the tidal cycles. From 1994 to 1997, these shorebirds fed in different tidal levels for the whole daytime leaving the intertidal area only during the high tide to roost nearby. In 1999 and 2000, the red knots limited their feeding activity to a half tidal cycle, from high to low tide. Then they abandoned the beach and came back on the next high tide. Based on the analyses of faeces we concluded that the diet at the alternative feeding area was similar to that in Fracasso beach. The only possible place where these prey items might be found in Nuevo Gulf, 20 km away, where tides occur half a cycle later. As far as we know, this is the first time that such a drastic change in the daily pattern of habitat use is described for red knot.