BIRD ADAPTATIONS 



described for the white rat (Cottle and Carlson, 1956), but the few 

 experiments done by Hart (in press) indicate that curarized pigeons 

 ( Columba liv ia) are not able to increase their metabolism in the 

 cold. 



Recent work by Steen and Enger (19 57) on pigeons and by West 

 (unpublished) on Evening Grosbeaks and Common Redpolls indicate 

 that shivering is the major source of heat production by birds in the 

 cold. Experiments on the Evening Grosbeak show that these birds 

 shiver all night out-of-doors at all temperatures below thermoneut- 

 rality in both summer and winter. The intensity of shivering in- 

 creases as the ambient temperature falls (Fig. 5) . 



Since shivering in particular and metabolic thermoregulation 

 in general are achieved by an increase in energy expenditure, it 

 is pertinent to review some of the recent work on energy exchange 

 in wild birds. 



Indirect calorimetric measurements of heat production can be 

 made either by recording the respiratory exchange of oxygen and 

 carbon dioxide or by recording food consumption and excrement 

 production. Although the first method has been widely used by most 

 workers, it is limited in that metabolic rates are sampled over rel- 

 atively short periods of time. Both "open circuit" and "closed 

 circuit" apparati have been employed, the latter being further re- 

 stricted because the ambient temperature must remain constant. 

 Energy balance studies such as those used by Kendeigh (1949), 

 Seibert (1949), Davis (19 55), King and Earner (1956), West (1960), 

 and Cox (1961) for wild birds yield an average metabolic level over 

 a period of several days. However, this method is not able to dis- 

 tinguish between metabolic levels at different times of the day. 



Automatic recording oxygen and carbon dioxide analyzers have 

 been successfully used to record oxygen consumption and carbon 

 dioxide production simultaneously for 2 to 3 days at a time on wild 

 birds. The birds live in small cages and are supplied with food and 

 drink ad libitum. Daytime and nighttime values can easily be obtained 

 by examining selected portions of the record (Fig. 6). Another ad- 

 vantage of this system is that the birds are not disturbed once the 



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