The Influence of Ambient Temperature on Diet in the Great Tit

In winter, Great Tits Parus major have a mixed diet of insect food and seeds. Field data suggest a dietary shift towards seeds with declining ambient temperatures. We hypothesised that Great Tits increase their preference for seeds with decreasing temperatures to raise their fat intake over time. An experiment was carried out to test whether this dietary shift with temperature exists. Six Great Tit females, held in captivity and acclimatized to winter conditions, had free access to two food types that differed in fat content. The ambient temperature was manipulated during the night, and for both food types the consumption and digestibility were estimated. During the night the energy expenditure was estimated using indirect calorimetry. Neither the digestibility of fat, nor the energy metabolization was related to ambient temperature. Evening weight, nocturnal energy expenditure, net food consumption and metabolizable energy intake were higher at lower temperatures. The proportion of fat in the diet was independent of the night temperature. There is no evidence that the preference for a fat-rich diet in Great Tits is affected by ambient temperatures.