are birds and mammals warm blooded

VIRGIL BRACK ( is founder and principal scientist at Environmental Solutions & Innovations, Inc., Cincinnati, OH. Search for other works by this author on:

JUSTIN BOYLES is associate professor at the Cooperative Wildlife Research Laboratory, Center for Ecology, and School of Biological Sciences, Southern Illinois University, Carbondale. Search for other works by this author on:

TED CABLE is professor emeritus, Park Management and Conservation, Kansas State University, Manhattan. Search for other works by this author on:

Virgil Brack, Justin G. Boyles, Ted T. Cable; Warm-Blooded Mammals: An Enduring Misconception. The American Biology Teacher 1 December 2022; 84 (9): 529–534. doi:

As researchers, teachers, and practitioners we often encounter young professionals and lay adults who do not understand basics of mammalian body temperature regulation. Often their single solid piece of knowledge is that some vertebrates (mammals and birds) are warm-blooded and some (fish, amphibians, and reptile) are cold-blooded, which is incorrect. There are many thermal capabilities and regulatory strategies. We provide basics of body temperature regulation, including definitions, its evolution, examples of body temperature variability, unique examples of hibernation and torpor, and we explain how a better understanding benefits individuals in personal and professional lives. We suggest a simple replacement of the warm-blooded paradigm that can be used to inform even young students. As a starting point, students young and old are familiar with species of mammals (e.g., platypus and opossums) that do not maintain as constant or as warm of a body temperature as humans and dogs. Students also know that humans do not maintain a constant body temperature over time (they have a “temperature” when sick) or all part of their body (they have cold hands and feet outside in winter). Keywords:

Heat generation edit

Body heat is generated by metabolism. [5] This has to do with the process by which glucose is broken down chemically in cells to produce carbon dioxide and water as well as adenosine triphosphate (ATP), a high-energy molecule that powers various cellular functions. One such metabolic process that produces heat energy is muscle contraction [6]. Friction caused by blood flowing through the vascular system also produces heat.

Food and other inputs are metabolized by all organisms, but some use the output more effectively than others. Metabolism is relatively inefficient, similar to all energy conversions, and approximately 60% of the available energy is converted to heat instead of ATP. [7] In most organisms, this heat dissipates into the surroundings. But compared to other animals, endothermic homeotherms—also known as “warm-blooded” animals—not only generate more heat but also have better ways of holding onto and controlling it. Their basal metabolic rate is higher, and they can raise it even more when engaging in intense activity. In order to retain body heat, they typically have well-developed insulation, such as feathers in birds and fur and blubber in mammals. They may shiver if their insulation is insufficient to keep their body temperature stable. Shivering is characterized by rapid muscular contractions that quickly deplete ATP and trigger cellular metabolism to produce more heat. Furthermore, brown adipose tissue with mitochondria capable of non-shivering thermogenesis is present in nearly all eutherian mammals. Through the use of an uncoupling protein, the mitochondrial gradient is directly dissipated as heat in this process, “uncoupling” it from its typical role of stimulating ATP production through ATP synthase.

These creatures use evaporative cooling in warm settings to expel extra heat, either by panting (all birds) or sweating (some mammals). Poikilotherms typically lack these mechanisms.

Terminology edit

In general, warm-bloodedness refers to three separate categories of thermoregulation.

  • Certain creatures have the capacity to regulate their body temperature internally, such as by shivering their muscles or speeding up their metabolism. The opposite of endothermy is ectothermy.
  • Regardless of outside influences or temperature changes, homeothermy[b] keeps the body’s internal temperature constant. Usually, the constant temperature inside is greater than the outside temperature. The opposite is poikilothermy. The Argentine black and white tegu is the only species of lizard that is known to exist among homeotherms, along with birds and mammals. It is thought that some extinct reptiles, including plesiosaurs, ichthyosaurs, pterosaurs, and some non-avian dinosaurs, were homeotherms.
  • Tachymetabolism[c] maintains a high “resting” metabolism. In essence, tachymetabolic creatures are “on” all the time. Even while their active metabolism is still many times faster than their resting metabolism, this difference is frequently not as noticeable as it is in animals with bradymetabolism. Animals with a tachymetabolic metabolism have a harder time surviving in a food shortage. [citation needed].

Varieties of thermoregulation edit

A considerable fraction of what are usually called “warm-blooded” creatures, such as birds and mammals, display all three of these categories (i e. , they are endothermic, homeothermic, and tachymetabolic). But over the last thirty years, studies in the field of animal thermophysiology have revealed a number of species that fall into these two groups but do not fulfill all of these requirements. For example, many small birds and bats undergo bradymetabolism and poikilothermy while they sleep (or, in nocturnal species, during the day). For such creatures, the term heterothermy was introduced.

Additional research on animals that have historically been categorized as cold-blooded has shown that the majority of these species exhibit different combinations of the three terms mentioned above as well as their analogues (ectothermy, poikilothermy, and bradymetabolism), resulting in a wide range of body temperature types. Some fish have warm-blooded characteristics, such as the opah. Because their brains and eyes are kept above room temperature by circulatory systems, swordfish and some sharks are better able to identify and respond to prey. [1][2][3] Some sharks and tunas share muscular mechanisms that increase their endurance when swimming quickly. [4].


What animals are warm-blooded but not mammals?

Non-mammals can generate body heat, for example a python and some species of fish, such as tuna. A reptile basking in the sun can become as warm to the touch as a mammal and its lethal temperature may be higher than that of many mammals.

Are humans warm-blooded mammals?

Mammals include humans and all other animals that are warm-blooded vertebrates (vertebrates have backbones) with hair. They feed their young with milk and have a more well-developed brain than other types of animals.

Why are birds warmer than mammals?

Insulation from the feathers, and the heat generated from hard-working muscles, both lead to a higher internal body temperature. Even then, mammals can sweat to cool down, but birds do not have sweat glands. They only lose heat through their exposed skin and respiratory system. This heat isn’t pointless.

What are 5 warm-blooded animals?

Animals whose body temperature does not change with the surrounding temperature. It includes birds and mammals. Dogs, human, cats, vulture, raccoon, and dolphin come under the category of warm-blooded animals.