Changes in the condition of dunlins and knots during short-term captivity

Dunlins, Calidris alpina, and knots, Calidris canutus, captured while roosting at Teesmouth in northeastern England, were held in captivity during ringing operations. During this time they lost up to 19% (dunlins) and 23% (knots) of their total mass. In dunlins, loss of mass occurred in two phases. During phase 1 (0–8 h after capture) mass was lost at a similar, declining, rate regardless of conditions or frequency of handling. During phase 2 (>8 h after capture), frequently handled birds continued to lose mass rapidly, but the mass of less disturbed birds decreased at a lower, constant, rate. Knots had a similar two-phase mass loss. Changes in body condition were analysed in less disturbed birds. During phase 1 much of the loss was due to dehydration. Fat catabolism began within 4 h of capture at a rate of 2.2 to 2.4 times basal metabolic rate (BMR) in dunlins and 2.4 times BMR in knots. Dunlins also lost lean dry muscle tissue concurrently and at a constant rate. After 24 h, dunlins had lost 27.4% of the protein reserve available in their pectoral muscles. The consequences of the stress of capture and handling on rates of loss of mass, particularly muscle protein, are discussed, as are the implications of short-term loss of mass for the accurate measurement of body condition in live and killed samples of birds.