Austral migration related to arrival time of Red Knot Calidris canutus rufa to Northern Hemisphere

GONZALEZ, PATRICIA; CARBAJAL, MIRTA; ALLAN BAKER; ECHAVE, MARIA EUGENIA; PISSACO, RUBÉN; BENEGAS, LUIS

Cadiz

Conferencia; International Wader Study Group Annual Conference; 2003

Wader Study Group

Arrival time of Red Knots at their last stopover before reaching the breeding grounds can be critical to adult survival and recruitment. To establish the relationship between the phenology of the austral migration and the arrival time at the last stopover in the Northern Hemisphere, simultaneous censuses were made from 2000 to 2003 in Argentinian Patagonia both at Rio Grande, Tierra del Fuego, where Knots spend their non-breeding season and San Antonio Oeste, Rio Negro (= SAO), the first main stopover site. In SAO abdominal profiles were sampled visually (Wiersma & Piersma 1995) as an index of body mass at arrival in early birds. Arrival and departure times in SAO was related to arrival in Delaware Bay, USA by resighting 823 birds colour-banded in SAO, with different marks for the first and the second half of March 1998, and 146 banded at the end of March 2003. In both localities scans of colour-banded and non-banded birds were made, and data were fitted to binomial models. In 2000 and 2001, Red Knots arrived early in SAO by direct flights, and had intermediate abdominal profiles. In 2002, however, Knots left Rio Grande 15?20 days earlier but most arrived in SAO 2 weeks later than previous years, and early birds had significantly lower abdominal profiles. This indicates that they had stopped in intermediate wetlands. In 2003 both early and late patterns were observed. Red Knots arriving early at SAO also arrived significantly earlier in Delaware Bay. These results suggest flexibility in migration strategies of Red Knots (?time selected vs energy minimizing?)