HUDSON 



HUDSON: This is the kind of thing that will just take more 

 measurements of different kinds of birds. 



WEST: I am interested in seeing the way your heart rate falls 

 off at the lower temperature, then goes flat; yet the metabolism 

 continues to fall. 



HUDSON: This may be a factor that is associated with hiber- 

 nation, because these are all species of birds and mammals which 

 have the capacity to hibernate or estivate. 



WEST; There must be a change in the stroke volume. 



HUDSON: Yes, if I can assume you mean that it is suggestive 

 that the stroke volume changes at the place where the heart rate 

 levels off? 



WEST: Yes. 



HART: Or the utiUzation. 



HUDSON: Yes, utiUzation or both. 



VEGHTE: What is the duration of the burst of heat? 



HUDSON: No more than a couple of minutes. 



WEST: I think this is probably a safe technique; we are try- 

 ing to measure heart rates in flight. We let the birds fly for a 

 few wing beats and as soon as they hit the ground, we get the 

 heart rate, which is extremely fast. We get it the instant that 

 they stop flying. I know there is a small lag there but I think that 

 this same heart rate does carry through. 



HUDSON: We have also been able to pick out rates that corres- 

 pond with the ones that we get where we have given them bursts of 

 heat from records that have very intense shivering on them. 



450 



