Which mammal is not able to regulate its body temperature?

Correct answer. It can not  regulate its body temperature. Its body temperature falls while inactive. Mammals are warm blooded animals, i.e., they can regulate their body temperature, have constant body temperature, without being influenced by outer environment. But some animals do not fall neatly into the categories of being warm or cold-blooded. Bats, for example, are mammals who cannot maintain a constant body temperature and cool off when they are not active. Echidnas maintain a range of body temperatures which usually lies between 77 and 98.6 degrees Fahrenheit and have difficulty cooling down. Mole Rats are another group of mammals who are unable to regulate their body temperature but they go deep down the ground to avoid temperature extremes.