PHYSIOLOGICAL ADJUSTMENT TO HEAT IN BLUE TIT PARUS-CAERULEUS NESTLINGS FROM A MEDITERRANEAN HABITAT

On Corsica Blue Tits Parus caeruleus ogliastrae breed late in the spri ng when ambient temperatures are high as a local adaptation to the lat e occurrence of their food. This means that Blue Tits rear their young when water demand of nestlings for evaporative cooling is high due to elevated temperatures, but the water content of the diet is low. Thus , the local environment may impose a water Limitation on breeding tits . We therefore expected physiological adjustments in Blue Tit nestling s to a hot climate with a low availability of water, such as a reduced metabolic rate. We measured oxy gen consumption and evaporative water loss of 20 full-grown nestling Blue Tits from Corsica in an open-flow respirometry system. Metabolic rate at thermoneutrality was only 0.11 7 W, significantly lower than expected from allometric relationships. Observed evaporative water loss at 25 degrees C was 40.8% lower than p redicted on the basis of body mass. The observed savings in evaporativ e water loss corresponded to the expected savings due to a reduced met abolic heat production. Thus, Blue Tit nestlings on Corsica are more s imilar in their physiological characteristics to species from hot and dry environments than to continental European Paridae.