Diet and energy budget of Red Knots (Calidris canutus rufa) in the Peninsula Valdes

MUSMECI, LUCIANA R.; BALA, LUIS O.; HERNÁNDEZ, MARÍA A.

Paracas

Congreso; VII Reunión de Aves Playeras del Hemisferio Occidental; 2017

During their northward migration, Red Knots (Calidris canutus rufa) regularly make a stopover at Fracasso Beach (42º 25´S, 64º 04´W), but its suitability as a stopover site in terms of birds? capacity to refuel is unknown. In April 2000 we studied the spatial feeding patterns, intake rate, diet, and energy density of prey in order to determine the daily rate of fat deposition. Our reconstruction of Calidris canutus rufa diet showed that 99% of all prey consisted on clams Darina solenoides and Tellina petitiana. The energy density in kJ.g-¹ (ash-free dry mass) was 23.2 and 11.5 for D. solenoides and T. petitiana, respectively. In combination with the measured defecation rates and time used during each of 6 tidal levels, the total energy consumption of Red Knots was estimated to be 279.8 kJ per half tidal cycle. Assuming an assimilation rate of 85% and a maintenance metabolic rate of 86.4 - 129.6 kJ, 108 ? 151 kJ were available to be converted into fat reserves. This equaled to a fattening rate of 2.4 ? 3.4 g per half tidal cycle, a value that was very similar to that obtained for other traditional stopover sites used by the species.