Survival of the Fattest: Body Stores on Migration and Survival in Red Knots Calidris canutus islandica

Severe summer weather in Greenland and Arctic Canada in 1972 and 1974 caused very poor breeding success and elevated adult mortality in red knots Calidris canutus islandica. We show that those individual knots that are known to have survived these summers were in better than average nutritional condition shortly before departure from their late spring staging area in west Iceland. The condition index of previously banded or subsequently recovered birds captured in Iceland was positively related to the number of summers they were known to have survived. Body stores carried from the last spring staging area to the breeding grounds appear to offer Arcticbreeding shorebirds significant selective advantages: they are used for physical transformation from migration to breeding condition, and in years when weather is difficult may enable survival after arrival on the breeding grounds.