Tachycardia during egg-hypothermia in incubating ptarmigan (Lagopus lagopus).

Incubating birds regulate the egg temperature by varying their posture and the distance between eggs and brood patch. In the present study, we show that this homeostatic process is further assisted by varying the brood patch blood flow according to the temperature of the eggs. When female ptarmigan resume incubation of cooled eggs (e.g. after a period of foraging), they immediately develop pronounced tachycardia (4 times noraml in wild, 2-3 times in captive birds). Tachycardia is maintained, although at decreasing intensity, until the eggs have obtained normal temperature. The eggs are heated 30 to 50% slower in females where tachycardia is inhibited by a beta-receptor blocking agent.