Cold-Blooded vs. Warm-Blooded Animals: 16 Differences, Examples

Differences between Cold-blooded and Warm-blooded animals
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Cold-blooded animals definition

Cold-blooded animals are the animals that are not capable of regulating their body’s temperature according to the temperature of the surrounding.

  • The body temperature of these animals fluctuates as they move in different surroundings with different temperatures.
  • Thus, they do not have a constant body temperature. Because of this reason, these animals cannot survive in extreme temperatures.
  • Cold-blooded animals include reptiles, fishes, amphibians, insects, and other invertebrates. These animals are also called poikilothermic animals.
  • Cold-blooded animals usually demonstrate any three of the thermoregulation mechanisms; Poikilothermy, Ectothermy, or Heterothermy.
  • Poikilothermy is the state where the internal temperature of the animals might vary, but the core temperature often remains the same as the ambient temperature of the immediate environment.
  • Ectothermy refers to the mechanism where the animals utilize external means like the sun, to control their body’s temperature.
  • Heterothermy refers to the mechanism where the body temperature might change drastically as the animal moves from one environment to another.
  • These animals have some mechanisms to have limited control over their body temperature. Most of them, however, utilize a combination of the above mentioned three mechanisms of thermoregulation.
  • As they move from one temperature to another, their body temperature might change drastically, so they have to depend more on external factors like sun and water to control their body temperature.
  • Some examples of this can be seen in lizards and crocodiles that stay in water during hot seasons and migrate towards the land by burrowing pits to keep them warm during the colder seasons.
  • The distribution of these animals is limited in the terrestrial and aquatic ecosystems because of their dependence on the environmental temperature for their metabolic activities.
  • Poikilotherms tend to have more complex metabolisms than their counterparts. For a single chemical reaction, they might have up to ten different enzyme systems, operating in different temperatures.
  • As a result, these animals have a more complex genomic structure than the warm-blooded animals occupying the same ecological niche as in the case of frogs.
  • Poikilothermic animals do not have complex, high-energy organ systems like brain or wings as their metabolism is so variable. Instead, they have some other adaptation like swimming muscles in fishes which can be warmed via heat exchange.

Warm-blooded animals definition

Warm-blooded animals are the animals that are capable of maintaining a nearly constant body temperature irrespective of the temperature of the environment.

  • Their body temperature thus remains the same as they move from one surrounding to another.
  • Warm-blooded animals have several internal mechanisms that help them warm up in colder areas and cool down in warmer areas. The control is mostly obtained by regulating their metabolic rates.
  • Warm-blooded animals include birds and mammals. These animals are also called homeothermic animals.
  • Warm-blooded animals, like cold-blooded animals, have different mechanisms for thermoregulation; Endothermy and Homeothermy.
  • Endothermy refers to the process by which various animals control their body temperature through internal means like burning fat, shivering, and panting.
  • Homeothermy is the mechanism utilized by various animals to maintain a constant internal temperature instead of varying external temperatures.
  • Most warm-blooded animals use a combination of these two mechanisms to maintain constant body temperature.
  • Although metabolic activities are mostly involved in controlling body temperature, various structural factors also play a significant role.
  • Some mammals have thick fur during winter and a thinner coat during summer. Similarly, depending on the species of mammal, they have sweat glands that are either present throughout the body (primates) or are localized (dogs).
  • Some homeothermic might not have enough food during the winter season to keep their metabolic activities going. Under such circumstances, these animals undergo a period of hypothermia called hibernation.
  • Because of their ability to survive in extreme environments, homeotherms exploit diverse and much more ecological niches as compared to poikilotherms.
  • Homeotherms also have simpler metabolisms as they do not have to change the metabolic processes as the surrounding temperature changes.

Key Differences (Cold-blooded vs Warm-blooded animals)

Basis for Comparison

Cold-blooded animals

Warm-blooded animals

DefinitionCold-blooded animals are the animals that are not capable of regulating their body’s temperature according to the temperature of the surrounding.Warm-blooded animals are the animals that are capable of maintaining a nearly constant body temperature irrespective of the temperature of the environment.
Also known asCold-blooded animals are also known as poikilothermic animals.Warm-blooded animals are also known as homeothermic animals.
TypesCold-blooded mechanisms can be broadly categorized as;


1.     Ectothermy

2.     Poikilothermy

3.     Homeothermy

Warm-blooded animals are classified into broad areas as;


1.     Endothermy

2.     Homeothermy

Body temperatureThey do not have specific body temperature as their body changes its temperature according to the surrounding temperature.Usually, their body temperature remains constant and ranges from 35-40°C.
Metabolic ratesMetabolic rates of cold-blooded animals depend entirely on the environmental temperature.In warm-blooded animals, environmental changes have no effect on metabolic rates.
PhaseThey undergo two phases to be protected from extreme climate. Hibernation is a resting phase in winter that may extend from weeks to months. Aestivation, which is a resting phase in summer.Most of them do not undergo any such phases as they can adapt to the changing environmental temperature. Some animals undergo a period of hypothermia called hibernation.
Organ systemPoikilotherms do not have high-energy organ systems like the brain.Warm-blooded animals have complex organ systems.
Heat regulationCold-blooded animals tend to regulate the heat in their body by activities such as stretching out limbs under sunlight, changing body colors, bathing in the sun, etc.Warm-blooded animals perform many varied activities to regulate the body heat that includes metabolic activities and adaptive activities such as sweating, panting, migration, changing the body surface area to body volume ratio, etc.
Resistance against microorganismCold-blooded animals have resistance against microorganisms, and when they are infected, they reduce body temperature as a defense mechanism.Warm-blooded animals have a much stronger immune system to defend against such microorganisms.
Energy productionThey gain energy in the form of heat to regulate body temperature for survival.They can easily produce heat within their body.
SurvivalCold-blooded animals cannot survive in any extreme temperature and conditions.Warm-blooded animals quickly adapt themselves to any environmental conditions and temperature.
Heat sourceThey mostly depend upon direct sunlight and heat from the surrounding environment.They produce heat from the consumption of foods.
Proteins Cold-blooded animals have multiple proteins, each of which performs at different temperatures.The proteins in warm-blooded animals are not temperature-specific.
Genome The genome in some cold-blooded animals might be more complex.The genome in most warm-blooded animals has simpler complexity.
Effect of body fatsExcessive fat causes overheating of the bodies of cold-blooded animals and might even lead to death.Fat is essential for warm-blooded animals as it helps maintain body heat, especially for animals like seals and whales, which live in freezing oceans.
Examples Animals like invertebrates, fishes, sharks, frogs, crocodiles, etc are some examples of cold-blooded animals.Birds and mammals are examples of warm-blooded animals.

Examples of cold-blooded animals


  • Fish is a group of animals that are cold-blooded and thus have a variable body temperature as they move through surroundings with different temperatures.
  • The water resources have different temperatures at different heights. Thus, when fishes move from one depth to another, their body temperature also fluctuates.
  • A sudden change in the environment might cause major shifts in metabolism, fluid-electrolyte balance, and acid-base relationship in fishes.
  • Thus, they employ behavioral and physiological thermoregulation mechanisms.
  • To achieve behavioral thermoregulation, fishes often move around to find water with appropriate temperature for their survival.
  • Some fishes like tunas and lamnid sharks have specialized anatomical adaptations for countercurrent heat exchange for conserving heat in the lateral swimming muscles.
  • Although the thermoregulatory centers in a fish cannot help provide a constant internal body temperature, they might serve to anticipate physiological changes that inevitably accompany thermal change.
  • Fishes residing in the polar region produce antifreeze that reduces the freezing point of the body fluid, thus protecting them against the cold water.


  • Crocodiles are cold-blooded reptiles that have variable body temperature.
  • Crocodiles have a preferred body temperature of 30-33°C and to achieve this temperature they move back and forth between the cold and warm parts of land and water.
  • These animals usually orient themselves to ensure that most of their body faces the sun. But as the body gets warm, they face the sun to reduce heat uptake by their small head.
  • They also open their mouth to cool down the brain through evaporative cooling.
  • Thus, they obtain thermoregulation behaviourally by exploiting their thermal environments.
  • Specialized peripheral nerve endings are present on the skin of most reptiles that can respond to variable environments.

Examples of warm-blooded animals


  • Birds are warm-blooded animals that have a constant body temperature that doesn’t change as the temperature of the surrounding changes.
  • Birds employ various metabolic activities resulting in heat production or loss to maintain the constant temperature.
  • The feathers on the birds protect them against extreme cold or scorching conditions.
  • Similarly, many birds like ducks tend to cover the unfeathered body parts like limbs underneath the feathers to prevent heat loss.
  • Physiologically, they increase the rates of metabolic activities to increase body temperature during colder temperatures. Some birds might mobilize into the water to lose heat through evaporative cooling.
  • The diversity in the ecological niche of birds is also due to their ability to withstand extreme temperatures by maintaining a constant internal temperature.


  • Mammals are warm-blooded animals, having a body temperature that remains constant even when the temperature of the surrounding changes.
  • The bodies of these animals remain covered with hair or fur that helps to keep the temperature constant.
  • Along with these structural features, several physiological and behavioral adaptations help with the internal temperature.
  • Different species of mammals exploit different ecological regions throughout the world as they have a different mechanism to adapt to those areas.
  • Thermoregulation in mammals occurs via various mechanisms. Some utilize heat production while others preserve the available heat.
  • The temperature control in mammals also functions as a defense mechanism against infections or attacks by different pathogens.


  1. Warm-blooded. New World Encyclopedia. 14 July 2020.
  2. Cold-blooded. New World Encyclopedia. 14 July 2020.
  3. CnawsHew, L. l. (1977). Physiological and behavioural reactions of fishes to temperature change. Journal of the Fisheries Research Board of Canada. 34:.730-134

About Author

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Anupama Sapkota

Anupama Sapkota has a bachelor’s degree (B.Sc.) in Microbiology from St. Xavier's College, Kathmandu, Nepal. She is particularly interested in studies regarding antibiotic resistance with a focus on drug discovery.

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