Winter energetics of the Capercaillie-a methodological approach

Abstract

The parameters of ecological energetics were measured using three groups of Capercaillie Tetrao urogallus : caged, enclosured and free-living birds. This comparison makes it possible to evaluate the usability of caged birds for studies on ecological energetics . Determining daily energy budget (DEB) in free-living birds bases on the quantity ofexcrements left in the snow burrow, estimation ofthe digestibility coefficients of food stuffs and time budgets of individual birds . Studies on free-living birds revealed the strong influence of diet on energetics . Gross energy intake (GEI) in males was around twice that of enclosured birds, while digestion coefficient was clearly lower. DEB of free-living birds was very close the DEB in the enclosure. Using body weight correction the difference was only 5 %. DEB values of males expressed as multiples of basal metabolic rate were in cages 1 .4, in the enclosure 1 .8 and in the field 1 .8 . This paper describes the techniques used in Russian studies on winter energetics of grouse, and it gives some examples of the application of the method. This example also confirms the usefulness of birds in captivity for studies on ecological energetics .