Aspects of the life-cycle energetics of two subspecies of Dunlin Calidris alpina
Dunlin from two breeding populations, C.a.schinzii from Iceland and C.a.alpina from northern Scandinavia, were studied during and after migration through Teesmouth, north-east England, and in captivity. C.a.schinzii winters in north-west Africa and has a much longer migration pathway than C.a.alpina which winters in Britain and around the North Sea. Measurements of Resting metabolic Rate (RMR) were made for the two subspecies of Dunlin in March and November in order to establish the relationship between resting metabolic rate and temperature and hence energy costs of living at different temperatures (20 C - 0 C). Energy costs of living in C.a.alpina were 21% higher than C.a.schinzii. Measurements of Basal Metabolic Rate (BMR) were made for the two subspecies (before, during and after moult) in conjunction with measurements of body compositions using Total Body Electrical Conductivity (TOBEC) in order to estimate the costs of moult. Energy costs of moult were 1692 KJ for alpina and 1016 KJ for schinzii.Energy costs of migration were estimated by measuring the amount of fat laid down before departure by wild Dunlin of the two populations, with the aid of Total Body Electrical Conductivity (TOBEC). Energy costs of migration were estimated as 3489 KJ for alpina, and 5156 KJ for schinzii. Energy costs of egg production and incubation were estimated from other workers’ studies of other (similar) species. Energy costs of egg production were only 220 KJ for the two subspecies whereas the costs of incubation were 1232 KJ and 1143 KJ in alpine and schinzii, respectively. In contrast to the suggestion by Drent and Piersma (1990), I have found that the costs of migration are considerably less than the costs of living. Also the total annual energy cost for those Dunlin wintering in colder areas i.e. C.a.alpina is much higher than for those wintering in tropical regions i.e. C.a.schinzii. Energy costs are not the only factors that affect a bird's lifetime output of young. C.a.alpina uses a different migration strategy to C.a.schinzii but may breed on better breeding grounds, and hence achieve more successful reproduction.