WEST 



IRVING: It is so hard to figure on some of these things in 

 examining the metabolism of the Brant in summer and winter. 

 The Brant is a big bird weighing a kilogram and a half, and with 

 feathers so thick that when you grasp hold of him you cannot feel 

 through the underlying bird or meat, and yet its metabolic rate 

 begins to increase at just about freezing temperature. It is a bird 

 with the thickest insulating feather cover that you can find, and yet 

 he does not use it for insulation. Of course the Brant, like the 

 other water fowl, follow the open water throughout the year and 

 perhaps they do not need any more insulation, but that does not 

 give any physical explanation. In fact, the explanation is probably 

 physiological rather than a matter of simple feather thickness. 



MORRISON: As far as changing body temperature goes, of 

 course this relation is related to difference between body tempera- 

 ture and ambient temperature. 



IRVING: Are you not working in a limited range of animal size 

 where the measurements are difficult? Perhaps life itself is diffi- 

 cult for animals of these very small dimensions and they have to 

 resort to metabolic subterfuges which are legitimate for them but 

 illegitimate from our point of view. They are difficult to examine 

 because you are looking at the 10 to 100 gram or so size range. 

 Perhaps some clarification would come if you went to larger birds; 

 I think your only representative above 100 grams was the pigeon, 

 was it not? 



WEST: Yes, I was concerned with the small wild birds, most 

 of the passerine group. 



PROSSER: Are you saying that this temperature- metabolism 

 curve rises continuously as you go to lower temperatures, and 

 that you have no thermo-neutral zone or critical temperature for 

 smaller birds, while in a larger bird there is a critical temperature? 



WEST: Yes. 



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