Behavioural Thermoregulation in Willow Ptarmigan Chicks Lagopus lagopus

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Abstract
The effect of behavior on the Tb [body temperature] of ptarmigan chicks was studied in captive and wild birds of different ages and at different ambient temperatures (Ta). Newly hatched chicks show inter-brood coordinated periods of brooding and browsing. During browsing Tb decreased; during brooding it returned to normal. At Ta from 7-10.degree. C the newly hatched chicks browsed for about 2 min and were brooded for 15-30 min. At the end of browsing periods their Tb averaged 37.1.degree. C; the lowest recorded value was 34.3.degree. C. Post browsing Tb showed little variation with ta but increased with age. No hypothermia was found in 3 wk old chicks. The duration of each browsing period increased both with increasing Ta and with age. If prevented from brooding, the chicks uttered distress calls when their Tb dropped below 34.degree. C, and they became lethargic at Tb below 32.degree. C. The sensory input which triggered the chicks return to brooding (the hen) appeared to be the decreased Tb rather than signals from the hen. Ta near freezing appeared to be a limiting factor for ptarmigan chicks during their 1st wk of life, especially if the food supply was scarce.