Shivering thermogenesis in leg and breast muscles of galliform chicks and nestlings of the domestic pigeon.

We studied the ontogeny of shivering thermogenesis in breast and leg muscles of precocial galliforms (domestic fowl, grey partridge, and Japanese quail) and the altricial domestic pigeon using electromyography (EMG) and indirect calorimetry. Galliforms were able to increase heat production by shivering in leg muscles at the youngest age studied (1-2 d). Pectorals contributed to heat production from days 7-10 onward, but in the partridge and especially in the fowl, shivering by the pectorals was weaker than in the quail. In the pigeon, shivering began in pectorals and legs at 2 and 4 d of age, respectively, and pectorals had clearly the predominant role in thermogenesis. Despite the early beginning of electrical signs of shivering, significant thermogenesis did not appear in the pigeon before the age of 6 d. All galliforms shivered in bursts, like pigeons aged 2-4 d. From the age of 6 d onward, continuous shivering became predominant in the pigeon. In pectorals of 2-6-d-old pigeons, shivering did not increase linearly during decreasing ambient temperature, as in other muscles and species, but started abruptly, at full intensity. Furthermore, in 2-4-d-old pigeons, cooling induced movement activity in legs. The median frequency of shivering EMGs varied (1) with maturation of the muscle, (2) with size of the adult bird, and (3) between altricials and precocials.