WEST 



MORRISON: I would like to return to the matter of the applica- 

 bility of these simple relations between metabolism and ambient 

 temperature, which was first raised by Dr. Johansen's talk. I do 

 not think that we should speak as though this relation is discredited 

 and not applicable in these animals. We must remember that these 

 represent limits which any animal will follow more or less closely. 

 They are limits of minimum metabolism and of minimum thermal 

 conductance and as such are excellent descriptive terms. Now, the 

 great deviation of your birds from the limiting curve is very inter- 

 esting as representing a physiological inefficiency since this extra 

 metabolism need not be expended if the bird were using the maxi- 

 mum potential of its insulation. It would be useful to describe the 

 bird both in terms of its limiting conductance, and also in terms of 

 its deviation from that limit. Perhaps this might be in terms of the 

 temperature range over which it deviates and the ratio of the meas- 

 ured and the basal metabolism at the critical temperature. 



WEST: I agree to that, but with these birds there is such great 

 deviation we should not force our data to fit the classical theory, 

 just because it is a classical theory. 



JOHANSEN: Critical temperature as a term is only meaning- 

 ful when we know that the core temperature stays constant up to 

 this point. 



MORRISON: I am not sure that the critical temperature has 

 been strictly defined in terms of these refinements. 



PROSSER: Why does a bird molt? It seems to me a most 

 wasteful thing. What is the advantage of getting rid of an old set 

 of feathers to grow a new set? 



WEST: They wear out. 



PROSSER: Are new feathers really better insulators? 



WEST: They probably are. I do not know, but they wear out. 

 From the behavioral standpoint, they have to grow their new colors 

 again for the fall and spring. We know that the total weight changes, 



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