Ardea
Official journal of the Netherlands Ornithologists' Union

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Visser J. (1978) Fat and protein metabolism and mortality in the Coot Fulica atra. ARDEA 66 (4): 173-183
In 1974 and 1975, 30 Coots were taken during mild weather conditions at the Westeinderplassen during the August-February period. In the first week of February in 1976, 12 Coots were col1ected during a cold spell. Some of these birds had died from starvation; others had been hit by cars. A few Coots in a very bad condition were killed. Al1 of these birds were weighed and analysed, i.e., the weights of three body components (fat, protein and water) were determined. Due to bad environmental conditions, the Coots collected in February of 1976 were significantly lighter than those collected during the August-February period in 1974 and 1975. The differences in the weight of the body components of 'normal' and 'starved' birds are discussed. The 'starved' birds had lost a considerable amount of fat, but also some protein. The body composition of 'normal' and 'starved' Coots in relation to dry weight shows remarkable differences. The decrease in dry weight in 'normal' birds in coupled with a distinct decrease in fat weight. This correlation is less pronounced in the 'starved' birds, due to the fact that most of the fat reserves in this group were already used up. The decrease in protein is more pronounced in the 'starved' than in the 'normal' birds. Differences in body composition in relation to wing length are also discussed. Wing length was the only available measure of size applied in this study. The loss of fat and protein proved to be related to the size of the birds. When bad environmental conditions prevail, large birds lose more fat than small birds, but their percentage loss is smaller due to the large fat reserves of the long-winged birds in normal condition. The conclusion is that, due to their limited fat reserves, short-winged birds run out of fat and use up an appreciable part (46%) of their protein reserves. Therefore, mortality due to bad environmental conditions can be expected to be related to body size. Since we know the relationship between body weight and fat content in 'normal' birds, the mean fat content in January (when body weight is lowest) could be calculated over the 19671976 period. Although the variation of the mean body weight in the successive winters is striking, there are no winters in witch the calculated fat content reached critical values for any group. This indicates that there was no unusually high mortality in the winters of 1966/ 1967-1976/1977. This conclusion was confirmed by observations in the study area.


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