The Bioenergetics of the Tufted Duck Aythya Fuligula (L.)

Abstract

This study formed part of the International Biological Programme project, to study the flow of energy through a fresh-water ecosystem, at Loch Leven, Kinross, Scotland. The Tufted Duck Aythya fuligula was the only duck species which fed entirely from within the loch and was present throughout the year; 500-550 pairs nested annually and there were 2000-4000 birds in late summer, but fewer than 100 birds overwintered. Chironomid larvae accounted for 60% of the food of the Tufted Duck at Loch Leven; other important foods were caddis larvae and molluscs (the latter were eaten during egg production). There was no competition for food with other diving ducks on the loch – Pochard Aythya farina, Goldeneye Bucephala clangula, but diurnal and seasonal variations occurred in the availability of food organisms to the ducks. Carcass analysis of 100 ducks taken throughout the year showed a pre-laying peak of reserves in the female, which provided all the fat and half the calcium for egg production. The remainder was obtained from food eaten during egg formation but reserves were the major determinant of clutch size. A similar amount of body reserves was retainer by the female for use during incubation, but again reserves were supplemented by feeding and food availability during incubation may be an important determinant of nesting success. Males were heaviest during winter but in all birds weight varied considerably in this season. Normal reserves were sufficient for at least 10d without food. Liver and Pectoralis muscle analyses showed that, except in cases of starvation, they would not be good indicators of the bird's 'condition'. Liver weight varied diurnally in relation to feeding and in the long term with the overall plane of nutrition. Pectoralis muscle normally provided only a small protein reserve but in extreme starvation was considerably depleted. This was seen in Scaup Avthva marila taken after an oil spillage, but many birds died of exposure before their reserves became exhausted. The most important parameters in the energy budget were numbers and respiration energy. The annual consumption by Tufted Ducks was equivalent to less than 5% of the chironomid production and they are therefore unimportant as consumers, compared with Trout and Perch. Food availability, to the ducks, apparently limits clutch size (through the build up of reserves), nesting success and autumn and winter numbers of the Tufted Duck at Loch Leven.