Energetics of the annual cycle of Dippers Cinclus cinclus

Abstract

Time‐activity budgets and energy expenditure of Dippers Cinclus cinclus were studied in all months of the year and for every stage of the annual cycle. The commonest daytime activity was feeding (54%), then resting (43%) and flying (4%). On a 24‐hr day basis the most marked changes in activity followed from changing daylengths. DEE (Daily Energy Expenditure), derived from time‐activity budgets through the year and laboratory estimates of metabolism, averaged 201 kj d ‐1 in females and 228 kj d ‐1 in the larger males. Over a more restricted range of circumstances, direct estimates of DEE obtained from 77 Dippers using the doubly labelled water technique averaged 205 ± 43 kj d‐1 and 251 ± 55 kj d‐1 in females and males, respectively. Overall, the correspondence between these largely independent estimates of energy expenditure was reasonably close. DEE was highest during breeding (laying‐females; rearing‐males) and in late winter for both sexes. The lowest energy expenditures occurred during moult, amongst juveniles and in early winter. Incubating females and mate‐guarding males also had low energy costs. Across all stages of the annual cycle body size, activity patterns, ambient temperature and river flow had significant effects on energy expenditure. The rate at which food was gathered to meet these changing energy demands varied widely. While some of this variation was imposed by a seasonal environment, it was also likely to reflect adaptive shifts in rates of food gathering, in some cases consequent upon the changing fitness benefits of various non‐feeding activities.