caloricity

from The Century Dictionary.

• noun The power in animals of developing the quantity of heat necessary to life and to enable them to resist atmospheric cold, so as to preserve at all times and in every part an internal temperature nearly equal.

from the GNU version of the Collaborative International Dictionary of English.

• noun (Physiol.) A faculty in animals of developing and preserving the heat necessary to life, that is, the animal heat.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun ectothermy