The Auk

Abstract

During the boreal winter, New World Red Knots (Calidris canutus rufa) principally occupy two areas widely separated in latitude. The larger group of approximately 100,000 birds is distributed along the Patagonian Atlantic coast, the smaller group of about 10,000 along Florida's Gulf coast. Resightings of banded individuals showed no interchange between these groups. The annual survival rate of knots marked in Florida is twice that of marked knots that winter in Patagonia. During northward migration Florida knots were sighted significantly less often at a major New Jersey stopover site than knots marked in Argentina. Whether this segregation is maintained during the breeding season is unknown. Wing and culmen lengths did not differ between the groups. The higher survival of individuals from the smaller Florida group, which presumably migrates a much shorter distance than the Argentina birds, runs counter to current evolutionary theories on the benefits of migration.