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 spring when ambient temperatures are high as a local adaptation to the late 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 nestlings to a hot climate with a low availability of water, such as a reduced metabolic rate. We measured oxygen 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 0.117 W, significantly lower than expected from allometric relationships. Observed evaporative water loss at 25 degree C was 40.8% lower than predicted on the basis of body mass. The observed savings in evaporative water loss corresponded to the expected savings due to a reduced metabolic heat production. Thus, Blue Tit nestlings on Corsica are more similar in their physiological characteristics to species from hot and dry environments than to continental European Paridae.

Nager R.G. & Wiersma P., ARDEA 84 (1): 115-125.