20 



SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 72 



Table 2. — Continued 



These helpless young are evidently as dependent upon brooding by 

 a parent to maintain their bodily heat as are eggs before hatching. 

 Apparently the body temperature may be considerably reduced, how- 

 ever, without permanent injury so that the body heat may sink as low 

 as 97° without death resulting. Even where nestling birds have devel- 

 oped contour feathers the temperature still remains considerably below 

 the average for the adult. When the bird leaves the nest at once there 

 is agreement between the degree of bodily heat that it develops and 

 that present in the adult. 



The single observation recorded for a young mourning dove is 

 apparently anomalous as it averages higher than those given for other 

 altricial birds. This is of interest as the doves have distinct afifinities 

 with groups having precocial young but in the Columbidae the imma- 

 ture birds, though covered with down at birth, are confined to the 

 nest until able to fly. Further study of young doves and of other down- 

 covered young that do not leave the nest when first hatched, as young 

 hawks, owls, turacos and others, will be of interest. 



From this discussion it may be stated with apparent certainty that 

 in birds with precocial young the mechanism of temperature control 

 is wel] organized at birth, while in species with altricial offspring this 

 power is so feebly developed that these birds are largely dependent 

 upon the parents for heat. The ability of perfect temperature con- 



