Morrison R.I.G. (2006) Body transformations, condition, and survival in Red Knots Calidris canutus travelling to breed at Alert, Ellesmere Island, Canada. ARDEA 94 (3): 607-618

This paper reviews the nutrient storage dynamics and body changes of Red Knots Calidris canutus islandica during migration through their final spring stopover area in Iceland and after arrival on the breeding grounds in the northeastern Canadian High Arctic at Alert. In Iceland, Knots not only accumulate large stores of fat and protein, but also undergo extensive morphological changes (increases in ‘flight machinery’ – flight muscles, heart, fat – and decreases in ‘baggage’ – stomach, intestines, leg muscles) that leave them well adapted for the flight to the breeding grounds. At Alert, early arrivals have substantial stores of fat and protein remaining. Subsequent body changes involve a rapid loss of these stores and a simultaneous rebuilding of various organs (e.g. restoration of digestive apparatus, development of gonads) which transforms them from a state adapted for flight to one that is suitable for breeding. Stable isotope studies show few of the stores, if any, are used for egg production. The stores could also be used as an energy source for early season survival during food shortage or poor weather. Their major purpose, however, may be to fuel the physical changes needed for breeding. The level of stores acquired at the final stopover during migration can affect survival in several ways. (1) Enhanced survival under difficult conditions: birds captured in Iceland and known to have survived a series of particularly severe summers had been in significantly better condition when caught than birds for which there were no subsequent records. (2) Longer average survival: for previously-banded birds captured in Iceland there was a positive relationship between numbers of summers survived and their condition in Iceland. (3) Reduced survival associated with inadequate stores; in North America, many rufa Knots passing through the final stopover area in Delaware Bay, USA, were unable to acquire adequate stores in the period 1997–2002 – this led to a dramatic decrease in annual survival rate, which was enough to account for a 50% decrease in the wintering population in Tierra del Fuego. Failure to maintain adequate habitat and food resources required by Knots and other shorebirds at their final spring stopover areas will almost surely lead to reduced reproductive success and survival, and consequent population decline.