BIRD ADAPTATIONS 



insulating ability have been made for several species of birds at 

 thermoneutrality and at a few lower temperatures (Hart, 1957; 

 Misch, 1960; Wallgren, 19 54; West, unpublished). Investigations on 

 the Evening Grosbeak ( Hesperiphona vespertina) and calculations 

 based on data in the literature indicate that the total insulation 

 (Body T - Air T/(kcal x bird x hour)) increases gradually as tem- 

 perature falls (Fig. 4). It can be readily observed that the insulation 

 increase is almost linear for some species (Tree Sparrow, Spizella 

 arborea ) , but a curve for most. The highest temperature at which 

 insulation reaches its maximum is C in both the Cardinal ( Rich - 

 mondena cardinalis) and the Evening Grosbeaks studied by Dawson 

 and Tordoff (1959), while many species continue increasing their 

 insulation to the lowest test temperature (House Sparrow, Passer 

 domesticus , and Variable Seedeater, Sporophila aurita). 



Conservation of heat at cold temperatures by peripheral blood 

 flow control and vascular heat exchange in non- insulated portions of 

 the body has been demonstrated in the Glaucous- winged Gull (Larus 

 glaucescens) (Irving and Krog, 1955) and in many other species 

 (Bartholomew and Dawson, 1954; Bartholomew and Cade, 1957; 

 Scholander, 1955). 



At air temperatures approaching body temperature, insulation 

 is decreased to its minimum, and mechanisms for dissipation of 

 heat are invoked. These include increase in peripheral blood flow 

 to the legs and feet, increased ventilation, evaporation from the 

 respiratory surfaces, and panting. Some birds are able to increase 

 the temperatures of their legs and feet and still maintain a favorable 

 gradient for heat loss even attemperatures above body temperature 

 (Bartholomew and Dawson, 1958). Birds living in hot regions have 

 evolved behavior patterns enabling them to avoid the heat of day. 



Metabolic mechanisms. Thermogenesis in reponse to cold 

 occurs chiefly by increased physical activity such as exercise, in- 

 creased muscle tone, and shivering. The heat produced by the spec- 

 ific dynamic action of digestion and assimilation may help to main- 

 tain body temperature, but evidence for this is lacking in wild birds 

 (King and Earner, 1961). Non-shivering thermogenesis has been 



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