Thermoregulation

When it's zero fahrenheit outside, I look at the birds and wonder how they do it. 

Talk about warmblooded, I think. Then I remember - that word is out:

Both the terms "warm-blooded" and "cold-blooded" have fallen out of favor with scientists, because of the vagueness of the terms, and due to an increased understanding in this field.

"Endothermic" is more of a current term.

"Warmblooded' is old-fashioned -

and carries connotations which concern
personal lives that burn 
with persistent passion.