Question

How do endotherms stay warm?

Answer 1

Endotherms or warm-blooded animals are those animals who are able to maintain internal or core temperature at a constant value irrespective of the ambient or external environment temperature. Only mammals and birds have developed this ability to maintain constant body temperature. Although few fishes such as Opah are also warm-blooded. Rest other animals are ectotherms that mean they depend upon the external temperature. The most commonly accepted body temperature is 98.6 °F. Although it might vary from species to species.
The process of making constant internal temperature is called homeostasis.
Any process or the ability of an organism that helps in maintaining the constant and stable internal environment is called homeostasis. Examples of Homeostasis are water-mineral concentration, various chemical levels of the body and body temperature.

Complete answer:
Temperature is a vital factor for survival because of various enzymatic reactions, metabolism, and physiology work best at a constant temperature.

Endotherms maintain a constant body temperature by:-
-Size and shape of the animals: Very large mammals such as whales, elephants as their body volume is so large can not depend upon the external environment to heat them and cool them down. It would not be efficient for their survival and generate heat internally. Some mammals which are so small such as sparrows and squirrels have less body surface area through which the dissipation of heat is less. This is achieved by having round bodies.
This is in accordance with Allen’s rule which states that 'in warm-blooded species, the relative size of exposed portions of the body decreases with the decrease of mean temperature'. Extremities (tails, ears, and beaks) tend to be smaller/shorter in a cool environment, thereby reducing surface area and heat loss.

-Generating energy: Warm-blooded animals so much energy to maintain constant body temperature and this is done by eating a lot more than their body weight. Generation of heat is totally dependent upon their mass while dissipation of heat depends upon the surface area of the animals. And this is the reason Smaller warm-blooded animals lose heat more quickly. So, it is easier to stay warm by being larger. Therefore food is a survival of life and death for warm-blooded animals. In contrast to warm-blooded animals, they require a lot less energy to survive.

-Migration: Some migratory birds such as the Siberian cranes migrate to relatively warmer climates to cope with the extremely cold environments.

-Hibernation: Animals such as polar bears who can not migrate past this extremely cold environment by going into a long sleep. This enables animals to conserve energy when food is scarce. During hibernation, body temperature drops, breathing, and heart rate slows, and most of the body’s metabolic functions are put on hold in a state of quasi-suspended animation.

Note: Eurythermal organisms are the organisms that can tolerate and live in a wide area of temperature whereas Stenothermal organisms are the organisms that cannot tolerate a wide range of temperatures. They will be restricted to certain areas only.