Parental Energy Expenditure During Brood Rearing in the Great Tit (Parus major) in Relation to Body Mass, Temperature, Food Availability and Clutch Size

Abstract

1. Quantification of the energetic needs of reproducing animals provides a basis for understandingp atternsi n reproduction.T he doubly labelled water techniquee nables this to be carried out under natural conditions. 2. Daily energy expenditure of 32 female Great Tits (Parus major) tending nestlings 11-12 days old (DEEpar) and energy expenditurea t night of five females was measured using the doubly labelled water technique. 3. Average DEEpar was 95. 1 kJ (24 h)- (1 -OW) and close to most predictions based on interspecific allometric relationships. Night metabolism was estimated to be 0.68 W. 4. Individual variation in DEEpar could be explained by variation in body mass (+), ambient temperature (-), clutch size (+) and food availability (-) but not by female tarsus length, age, brood size or nestling mass. The significant factors together accounted for the differences found between years and broods and explained 64% of the variation. Possible causal path-ways are discussed. 5. The DEEpar in Great Tits was related to body mass with an exponent of 1 99; signifi-cantlys teepert hant he interspecifice xponento f 0-67-075 reportedi n the literature. Analysis of intraspecific variation in DEEpar for 10 species tending young, revealed variable trends with body mass.