FACTORS INFLUENCING THE TEMPERATURE REGULATION OF BIRDS

Abstract

The normal body. temp. of the chick increases from that of its environment at the time of hatching to about 41[degree] C 10 days after hatching when it approaches and remains within the limits of the diurnal variation of the adult. Although both panting and shivering mechanisms are functional shortly after hatching, neither mechanism is efficient until after several days of post-hatching development This development is correlated with increasing metabolism and body temp., stabilization of thermotaxic control, and the transition from down feathers to the adult plumage. Both central and reflex shivering may be demonstrated but only central control of panting in the domestic fowl is believed to exist. Exposure to cold environmental temp. evokes periodic muscle tremors, vasoconstriction, and acceleration of breathing and heart rates. With progressive hypothermia, shivering becomes continuous until, like the heart and breathing rates, it gradually declines. Shivering ceases at a cloacal temp. of approx. 20[degree]C, breathing stops at 15[degree], but the heart may continue to beat at temps. below 10[degree]C. Respiration and cardiac function can be maintained at even lower temps. with adm. of O2. Neither the panting threshold nor thermal tolerance of pigeons was significantly altered at high temps. and humidity, but rapidly developing and severe hyperthermia could not be prevented. Although some variation exists in the lethal temp. of immature birds, an avg. lethal temp. for fowls may be taken as 47[degree] C.