Abstract
In a recent review of the adaptive role and regulation of winter fattening in birds, King & Farner (1966) concluded that information available at present does not permit a decision to be made as to the role of temperature in the regulation of fat depositionwhether a proximate or ultimate factor, or both. The present paper reports a study of yellow buntings (Emberiza citrinella L.) caught at a roost at Wytham, near Oxford, in the winter of 1966-67. Carcass analyses of samples of birds showed the levels of fat and other energy reserves carried by the birds on different dates, and in this paper these reserves are related to the calculated energy requirements for each night to determine the proportion of birds which should survive each roosting period (from dusk to dawn). The results arecontrasted with studies on bullfinches (Pyrrhula pyrrhula (L.)) made in the same locality by Newton (1969). Yellow buntings are mainly granivorous birds, which may feed up to several miles away from their communal roosts. However, recoveries of ringed birds (Spencer 1966) indicate that they move only short distances during their lifetimes, seldom as much as 10 miles. The same individuals may be caught at any one roost throughout a winter and in successive winters. Thus a given roosting population may be considered practically 'closed' for purposes of estimating survival.
Published Version
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