NO. 12 BODY TEMPERATURE OF BIRDS WETMORE I3 



amphibians, with their poorly developed lungs, gain the same end 

 by evaporation and radiation through their moist glandular skins. 

 There is a definite limit, however, to the degree of heat that these cold- 

 blooded animals may endure. In Arizona I have seen a Gila monster 

 {Heloderma suspectum) fresh from the desert perish when the sack 

 in which it was confined was inadvertently left exposed in the noon- 

 day sun for a period of fifteen or twenty minutes. 



Although in these cold-blooded animals there is a direct reaction 

 to external cold, with birds the case is entirely different. Some investi- 

 gators in making studies of avian body temperatures have been careful 

 to record the temperature of the atmosphere and to cite this data in 

 connection with their other records. After due consideration I have 

 not done this as I do not consider that there is any constant relation 

 between the normal temperature of the surrounding medium and that 

 of the body cavity in birds. After making careful records of avian 

 body temperatures at all seasons of the year, I am, in light of the 

 records available at present, unable to recognize any constant dififer- 

 ence between body temperatures made in the same species at seasons 

 of marked heat or marked cold. Where the individual is in normal 

 health and is sufficiently supplied with food, the agencies of tempera- 

 ture control will tend to maintain an even body heat. Any variation 

 that may occur, other than that incident to the daily rhytlimic rise 

 and fall of body heat, may be attributed to some other condition that 

 under normal conditions would disappear within a comparatively 

 short period through a readjustment of the bodily functions. Any 

 bird may, through inclement exposure, become thoroughly chilled and 

 so have a greatly reduced temperature but such a condition cannot 

 be considered normal. Thus an immature white-faced glossy ibis 

 (Plcgadis guaraiina) exposed for half an hour to a severe rain and 

 hail storm became so chilled that it could scarcely stand and shook 

 violently with cold. When warmed with hot towels and dried out 

 once more it was restored to its normal condition and soon was run- 

 ning about on the floor of the laboratory so far recovered that it 

 mischievously began to torment other smaller birds confined with it. 



Birds, however, may be divided roughly into two classes with regard 

 to their ability to adjust to external temperature. The first category 

 includes those able to withstand any reasonable degree of cold, while 

 in the second are included those species that migrate to regions where 

 cold in any degree is not encountered at the approach of inclement 

 weather. Broadly speaking, the question of difference between these 

 two groups is not so much one of change in external temperature as it 

 is of food supply. Thus species that feed on flying or crawling insects, 



