THE INFLUENCE OF BROOD SIZE ON THE ENERGY METABOLISM AND WATER LOSS OF NESTLING GREAT TITS PARUS MAJOR MAJOR

Abstract

Summary At normal outdoor temperatures there is a distinct influence of brood size on the heat production of ten‐day‐old Great Tits. One ten‐day‐old nestling proved unable to maintain its body temperature at 12 ° C. Two ten‐day‐old tits together in one nestbox at 12 Á° C were able to elevate the air temperature sufficiently to maintain homoiothermia. The same of course holds for tits in larger broods. At an air temperature of 18 ° C, six or seven ten‐day‐old tits placed in a nestbox elevated the air temperature to a level at which they almost reached a state of hyperthermia: their metabolism was at the basal level. The basal metabolism of a ten‐day‐old tit was found to be slightly more than 0–1800 kcal/h. The metabolism intensity of 12 tits in a nestbox at 12 ° C was of the same order of magnitude. Tits in broods comprising more than 12 or 13 nestlings at normal outdoor temperatures probably develop hyperthermia, which is unfavourable both for their energy and for their water balance.