Ardea
Official journal of the Netherlands Ornithologists' Union

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Mertens J.A.L. (1987) The influence of temperature on the energy reserves of female Great Tits during the breeding season. ARDEA 75 (1): 73-80
A study was made on the effects of the ambient temperatures during the reproductive period of Great Tits on their energy reserves. This was done by collecting female birds, respectively at the time they had laid their first egg, at the time of onset of incubation and at the end of the incubation period. It was found that the energy reserves of females (and associated with this the lipid content) decreased during the incubation period when the daily mean temperatures were below ca. 14ŚC. This decrease was almost entirely due to decrease of the lipid content. No influence of environmental temperatures during the egg-laying period on the energy reserves of the females could be established, but this is possibly due to the fact that the range of temperatures during the egg-laying periods in 1980, 1981 and 1982 was too small. At temperatures below 8 ŚC the female changes the nest construction during the incubation period in such a way that heat loss to the upper part of the nestbox, which is mainly due to convection, is reduced. The water content of the females also decreases during successive phases of reproduction in proportion to total body weight. This weight loss may reduce costs of flight. The findings strongly suggest with regard to energy, that especially the incubation period is a critical time for the female.


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