WEST 

 DISCUSSION 



JO HANSEN: I am very impressed with all the facts that are 

 available on birds now. I think this surpasses what we know about 

 mammals, particularly with regard to ecological factors involved 

 in temperature regulation. I was particularly pleased to hear your 

 doubts as to whether we really can consider the critical tempera- 

 ture as a fixed point, and also whether insulation is gradually 

 mobilized during the period of active increase in metabolism. As 

 I pointed out in my paper, I think this applies also to the more 

 primitive mammals. 



WEST; And I think also to the small mammals. 



JOHANSEN; Definitely. I had another question, and that is, 

 how does this ten-fold difference in electrical activity correspond 

 with the actual metabolic difference between the two? Could you 

 comment on that? 



WEST; We do not have the metabolism of the rats worked out 

 in calories. Also no simultaneous measurements of metabolism 

 and shivering have been done at a series of temperatures for 

 mammals. 



JOHANSEN; I was wondering whether you could correspond 

 metabolism with electrical activity. 



WEST: I have done it for birds but not for mammals. In birds 

 there is a linear relationship between electrical activity and meta- 

 bolism. The slope varies with the size of the bird. So far we have 

 plotted data for three species and the smallest, the common red- 

 poll, increases its electrical activity much faster than it does 



its metabolism. The larger birds do not increase their shivering 



o 

 as fast and there is about a 45 slope for birds of about 100 grams. 



HART: It is much higher for birds than it is for mammals. 



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