BIRD ADAPTATIONS 



PITELICA: I do not think they are present. I am not sure about 

 that. I have not looked for them, actually. If they are there at all, 

 they are certainly not easily noticed. 



HUDSON: I would like toadd toDr. Johansen's, Dr. Morrison's, 

 and Dr. West's remarks with respect to the lower critical tempera- 

 ture. In our laboratory we have had a number of cases in which we 

 have been unable to get nice extrapolations of the metabolic rate to 

 the appropriate body temperature, and in some cases we get extra- 

 polated body temperatures as high as 44 C and 45 C. At the same 

 time, using the same techniques and animals from similar areas, we 

 are also able to successfully extrapolate, so that we are reasonably 

 certain that it is notour technique, but have the feeling that possibly 

 there was some change in conductance going on even below the lower 

 critical temperature. 



PROSSER: May I ask just one more question about the computed 

 insulation curve? If similar curves are constructed for mammals, 

 what would be the shape and the value of the index that Dr. West 

 presented? 



HART; In lemmings, during activity there is a large variation, 

 but during rest in mice at least, the variation of insulation v/ith tem- 

 perature was similar to the hypothetical insulation curve for birds 

 except that it conforms more closely to the critical temperature. 

 In other words, the curve becomes flat at higher temperatures. If 

 body temperature is constant and the correlation between metabolism 

 and temperature extrapolates to zero at a value higher than body 

 temperature, then insulation would increase wath fall in temperature 

 in a manner comparable to that seen in birds. 



HUDSON; And these are also animals which have, from general 

 appearance, reasonably good coats, have metabolic rates that are 

 approximately what you would expect from their body size, but also 

 have lower critical temperatures that are extremely high, that is 

 above 30 C. So that on the basis of general judgment you would 

 expect the animal to have the capacity to continue his regulation by 

 physical means through much lower temperatures than he does. 



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