Bioenergetics of tufted duck (Aythya fuligula) at Loch Leven, Kinross.

Abstract

SynopsisThe tufted duck was chosen as the subject of an energy study at Loch Leven because it is a diving duck which feeds mainly from within the loch and it is present throughout the year, about 500 to 600 pairs nest annually.Using data from population counts, breeding biology and feeding studies and the analysis of body and egg composition an energy budget for the population has been computed. The values for respiration, R, are calculated on the basis that ‘existence energy’ requirements are 2·5 × Standard Metabolic Rate. Values for rejecta assume an assimilation efficiency of 75 per cent.The figures have been presented on a monthly basis as there are wide fluctuations in population size, and therefore energy demand during the year and between years. In 1970 very large numbers of tufted ducks were present on the loch during autumn. The additional demands of these birds over 4 months represent an increase in the annual energy requirements of almost 50 per cent.Chironomid larvae account for 60 per cent of the food of the tufted ducks at Loch Leven; other important food items are caddis larvae and molluscs (mainly Valvata spp.).Expressed on a /m2 basis and over a full year the energy demands of the tufted ducks represent a small proportion of the total energy available at Loch Leven. However, water depth and the depth of the food in the substrate reduce the actual availability of the food and probably reduce the usable feeding area to 20 per cent of the total loch area.