Plasticity in the utilization of beaches by the Red Knots at Peninsula Valdés, Patagonia Argentina: diet and prey selection

MUSMECI, LUCIANA; GATTO, ALEJANDRO; HERNÁNDEZ, MARÍA ÁNGELES; BALA, LUIS O.; SCOLARO, JÓSE A.

Vancouver

Congreso; IV Meeting Western Hemisphere Shorebird Group; 2011

Western Hemisphere Shorebird Group

The Red Knot Calidris canutus rufa utilizes some beaches of Peninsula Valdés (Patagonia, Argentina) as a trophic stopover on their northern migration. Since studies began in 1993 anduntil 1998, they regularly utilized Fracasso Beach and basing their diet on the clam Darinasolenoides. In 1998 a storm modified the beach sediments? granularity and its invertebratepopulations leading to a significant reduction on the trophic offer for the knots. The knotsstarted to feed at Colombo Beach, located in another gulf at 25 km of the previous one.Trophic ecology of C.c rufa was studied in Colombo Beach between 2002 and 2008considering their prey selection, diet richness and niche width. D. solenoides was thepreferred prey by the knots, and in some years the polychete Travisia olens was preferredinto their diet. The selected sizes of clams and their consumed biomass were in line withthose reported in other studies in Patagonia. Knots chose to feed at another intertidalenvironment and they incorporated a novel prey in their diet (polychetes) probably due to the low density of clams in Colombo Beach. The diet observed among years was significantlydifferent (ANOSIM P <0,001). This species has suffered an abrupt population decline andshowed a constancy in the use of places and prey where they stopover. There is important forits conservation that they have been able to adapt to these changes in Peninsula Valdésshowing a higher plasticity that in others stopovers sites on its migration.