Holmgren N., Ellegren H. & Pettersson J. (1993) Stopover length, body mass and fuel deposition rate in autumn migrating adult Dunlins Calidris alpina: Evaluating the effects of moulting status and age. ARDEA 81 (1): 9-20

The stopover of adult Dunlins, Calidris a. alpina during autumn migration at Ottenby, S.E. Sweden, was investigated. The proportion of Dunlins actively moulting their flight feathers was higher among second-year (2-yr) birds than among older ones (3-yr+). We compared stopover length, arrival body mass, departure body mass and rate of body mass increase between 2-yr and 3-yr+ birds, and between moulting and non-moulting birds, respectively. To estimate length of stopover, a simple mark-recapture model, assuming a constant stopover and capture probability, was fitted to the data on recaptured Dunlins. Maximum likelihood estimates of the daily stopover probability and its variance are provided. Second-year Dunlins made longer stopovers than older ones, but moulting and non-moulting birds did not differ in their stopover length. Rates of body mass change did not differ between age and moult categories. Nor did arrival body mass differ between the four categories. However, 2-yr birds gained more mass before departure than older ones did. Observed stopover length, body mass at ringing and body mass at last recapture were correlated with rate of body mass increase to investigate whether state-dependent decisions were made by the Dunlins. Stopover length appeared to be independent of both body mass at ringing and rate of body mass change in all age and moult categories, indicating that the simplifying assumption of a constant stopover probability in our stopover model was valid. In non-molting birds, body mass at ringing was negatively related to rate of body mass increase. The results are evaluated in terms of energy-minimised and speed-maximised migration.