Final answer:
The rate at which an endothermic animal uses energy while at rest is called the basal metabolic rate (BMR), which is essential for maintaining constant body temperature and is higher in smaller endothermic animals due to greater surface area relative to body mass.
Step-by-step explanation:
The rate at which an endothermic animal expends energy while at rest is called the basal metabolic rate (BMR). This rate is crucial for maintaining a constant body temperature regardless of environmental conditions. Endothermic animals, often referred to as warm-blooded animals, use insulation such as fur, fat, or feathers to conserve body heat. The BMR is a measure of the energy used by an organism to perform basic life-sustaining functions and is expressed in units such as joules, calories, or kilocalories.
It is interesting to note that smaller endothermic animals have a higher BMR per unit of body weight than larger animals, due to a greater surface area relative to their mass. Therefore, they lose heat more quickly and need more energy to maintain their internal temperature. Human males typically have a BMR ranging from 1600 to 1800 kcal/day, while human females have a BMR of 1300 to 1500 kcal/day.