This does not effect their lives because they live underground in an environment with a very stable temperature regime. Mammals are unique in possessing hair and in many mammals hair varies throughout the year. Why Warm Blooded Being warm blooded gives mammals a distinct advantage in may habitats, allowing them to be active when reptiles are hardly able to move. It also allows mammals to live in habitats where reptiles cannot live at all, such as the arctic, mountain tops, etc. The reason behind this is that muscle activity is basically dependent on chemical reactions, as are all biological functions.
Chemical reactions run slowly when it is cold, but quickly when it is hot.
The more energy you have the faster the chemical reaction occurs. In the early mammals being endothermic probably allowed them to be active at night when competing reptiles were forced to rest or be sluggish. Being warm blooded is costly. Mammals and bird have mush greater energy requirements than reptiles of a similar weight. In simple terms, small animals lose heat more quickly than larger ones, hence it is easier to stay warm if you are bigger.