Jenni L. & Jenni-Eierman S. (1987) Body weight and energy reserves of Bramblings in winter. ARDEA 75 (2): 271-284

The influence of ambient temperature and roost size on Brambling winter body weights was examined. Adult Brambling showed a negative correlation between body weight and mean daily temperature of the 2-5 days preceding weighing. This was not observed in first year birds. A comparison of mean body weights showed that birds in large roosts were considerably heavier than in smaller ones. Analysis of body composition showed that increasing body weight is first due to fat depositing. Above a body weight of 25 g it is also related to protein build up. Calculation of energy reserves demonstrated that the energy reserves of Brambling from large roosts are by far superior to other passerines in winter. They permit survival for several days without food intake, comparable to larger species. Significant protein reserves (together with more fat) are built up when the birds are able to starve for more than 24 hours and, thus, protein metabolism must draw completely on the bodies own reserves. The fat and protein reserves are interpreted as an adaption to the risk of snow fall which renders the food resources inaccessible in about half of the beech mast winters in Central Europe.