NO. 12 BODY TEMPERATURE OF BIRDS WETMORE 21 



trol is not fully matured until the young leave the nest. The early 

 development of this faculty in precocial young is in line with their 

 advanced stage as regards securing food, general activity, and ability 

 to care for themselves. According to Pembrey/ similar statements 

 regarding young birds have been made by Edwards.^ 



METHOD OF TEMPERATURE CONTROL IN BIRDS 



Bodily heat in all animals is caused by tissue changes during active 

 work performed by various organs or parts. Mills ' states that bodily 

 heat, though arising in great part from actual oxidations that take 

 place in the system, is in its entire amount best defined as the out- 

 come of all chemical processes that take place in the organism. In 

 so-called cold-blooded vertebrates the combined energy or rate of these 

 chemical changes is slow, so that heat is given off by the body almost 

 as rapidly as it is generated. In the groups that we class as warm- 

 blooded, Aves and Mammalia, these changes are more rapid and 

 intense so that heat generation may be in excess of heat radiation. In 

 the warm-blooded group there is also a more or less perfect control of 

 heat radiation when the body is normal in health. In homoiothermal 

 animals there is, therefore, an approximation to the maintenance of 

 a fairly uniform internal temperature, and the animal remains inde- 

 pendent of the ordinary rise and fall of the degree of heat of its 

 external medium. 



Bayliss ^ considers control of heat production (probably in muscles) 

 as the primitive method of temperature control. Among homoio- 

 thermal animals, the Monotremes (both Echidna and Ornithorhyfi- 

 chus) have the lowest body temperatures, as the average for these 

 species is only 85.6° Fahr. In the case of Echidna all regulation of 

 temperature appears to be through change in heat production as this 

 animal possesses no sudoriferous glands and shows no apparent change 

 in respiration at high temperatures. In cold weather it hibernates and 

 maintains a temperature only slightly above that of the air. The 

 duck-bill (Ornithorhynchus) has the power of regulating both heat 

 loss and heat production so that its temperature is maintained at a 

 more even level. The marsupials are intermediate in this respect 

 between monotremes and higher mammals. 



' Schafer, E. A., Text-book of Phys., London, Vol. I, 1898, p. 804. 



* " De I'influence des agens physiques sur la vie, Paris, 1824. (Not seen by 

 the present writer.) 



* Animal Physiology, p. 461. 



* Principles of General Physiology, 191 5, pp. 458-459. 



