NO. 12 BODY TEMPERATURE OF BIRDS WETMORE I5 



temperatures of individuals that I collected. Thus, two male violet- 

 green swallows (TacJiycincta thalassina lepida) registered 103.8° and 

 106.8°, respectively, a female black-throated gray warbler (Dendroica 

 nigresccns) 105.4°, a female Audubon's warbler {Dendroica audu- 

 honi) 105.6° and two purple martins (Prognc subis) 104.8° and 

 105.0°. Such abnormal records, due manifestly to lack of sufficient 

 food, were not included in the register giving the normal average 

 and range of temperature. That they were abnormal may be ascer- 

 tained by referring to other records given for these species. 



Birds that remain in regions where they are exposed to cold, be- 

 come more heavily feathered before the winter season so that there is 

 less radiation of heat externally. Correspondingly, in summer the 

 feathered covering is thinner, and the feathers themselves often 

 become more worn so they are less burdensome. With increased cold 

 there is apparently some readjustment to maintain the bodily heat 

 at its normal point. Were this not so the individual would become 

 affected so unfavorably that with prolonged exposure it would perish. 

 We must suppose a more rapid metabolism and a conservation of the 

 resultant energy in order to overcome this. Such a condition is not 

 difficult to imagine in hawks, crows, and other birds of large size, but 

 is wonderful when such feathered mites as the kinglets, creepers and 

 chickadees are considered. 



The part that the feet and tarsi of birds play in equalizing the 

 body temperature is difficult to state. In the majority of birds the 

 space from the lower end of the tibio-tarsus to the tips of the toes 

 is covered with skin in which are developed more or less perfect horny 

 scutes (the whole forming one of the most evident reptilian features 

 visible in the living bird.) The blood supply is of fair quantity clear 

 to the tips, of the toes, as blood trickles from slight wounds in the 

 foot. There is no evidence of a forced circulation yet in many cases 

 warm blood must be conveyed constantly to these parts to avoid frost- 

 bite. Many ducks, grebes and other aquatic birds remain during 

 winter just south of the line of ice. Swans, phalaropes and loons 

 appear in the Arctic regions with the first breaking up of ice. I have 

 seen auklets, puffins, and murrelets swimming and diving for hours 

 in Bering Sea with no apparent discomfort at a time when the tem- 

 perature of the water registered -^39° Fahrenheit. Mallards and 

 other wild ducks frequently clamber out of the water and stand about 

 on ice for considerable periods without visible hardship. How 

 these birds overcome or avoid the effect of cold upon their feet is a 

 mystery as yet. Although supplied Avith a certain amount of blood, 

 as has been stated, the feet and tarsi of birds are more often cold or 



