User blog comment:Lord Loss/Discussion of the Week: Portable 3rd Subspecies/@comment-3062343-20120527020930/@comment-1653324-20120528092444

Dax has a point (if Agnas were cold blooded). For warm blooded creatures, being smaller size means they can survive with less food. The problem with this is what place has more food, the arid Volcano or the cold Tundra.

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Loss, there is a problem with your heat capacity theory. Energy loss is directly proportional to mass and temperature change, with a constant called heat capacity.

q = mCΔT

So bigger creatures need a lot more energy and effort to maintain a proper body temperature. The 20 L of water just had more kinetic energy to start with (it had the same temperature as the 500 mL one, but greater mass), that's why it takes longer to cool.

Simply, a fat person burns more calories by shivering in a cold bath than a thin person does (without considering insulation, which only does a limited effect)

Other animals do away with this problem, by having longer fur or feathers, or thicker blubber, which have high insulative properties. They lose less heat, so require less energy.