14 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 72 



or on fresh fruits, must leave before a supply of this food fails. 

 Others that search out insects in hibernation, dried berries, or live 

 on seeds, pay little attention to the approach of chilling weather. The 

 question seems on the whole one of adequate food supply, that the 

 organism may receive its life-giving elements constantly. However, 

 forms that habitually experience cold weather during a part of the 

 year must have a greater development of reaction for temperature 

 regulation than do those of the other groups. Some species from the 

 category of those accustomed only to a hot climate may experience 

 severe cold without harm if supplied with proper food. Others suc- 

 cumb under these unusual conditions. Thus, Mr. N. Hollister, Super- 

 intendent of the National Zoological Park, informs me that red, blue 

 and yellow macaws (Ara niacao) confined in large flight cages, remain 

 outdoors at Washington, D. C, during the winter in perfect health. 

 An allied species however, the blue and yellow macaw {Ara araramia) , 

 was unable to withstand the cold and perished, though it throve during 

 warmer weather. From information available it seems that both 

 of these macaws in their normal range inhabit the tropical zone, and 

 are subjected to the same general conditions of life. 



There is a marked decrease in body temperature where food is not 

 obtained in suitable amount while the bird is subjected to cold. This 

 may be seen readily among our smaller insectivorous birds where they 

 are caught by a sudden return of cold weather during their northward 

 migration in spring. Decrease in bodily temperature from this cause 

 may be illustrated by the following: 



During the latter part of May, 1916, I was stationed at a small 

 field laboratory in Utah near the point where Bear River enters Great 

 Salt Lake. For several days preceding the evening of May 23 the 

 weather had been mild, and small migrant birds that nested in the 

 mountains had left the middle of the valley for the uplands. On the 

 night in question a cold wind with a driving rain came on and con- 

 tinued until ten the following morning, and there was little rise in 

 temperature of the air until late afternoon. A few Audubon's, pileo- 

 lated and yellow warblers and an occasional small flycatcher appeared 

 in the willows, and until noon there was a steady flight of swallows 

 down the river toward some haven on the flats below. To escape the 

 driving wind, the latter flew low over the river or beat along behind 

 shelter of the willows that fringed the stream. Hundreds passed, 

 travelling in little flocks so that for a time there seemed to be no end of 

 the constant procession of passing birds. These small birds were not 

 obtaining food as no insects were to be had and in consequence many 

 were suffering from a lowered vitality. This was reflected in the body 



