Why Are Whales Mammals?

Whales are classed as marine mammals, and in this article we look to find out whether they possess all the mammalian traits.

Whales breathe air, give birth to live young, provide milk, have a small amount of fur, and are warm-blooded.

Many people have asked me about whales being mammals so in this article, I look at how whales are classed as marine mammals.


When thinking about marine life, we think about fish, including sharks and rays; we may even think about corals, which are, in fact, animals and not plants. The largest animal that has ever lived falls into the category of mammals.

With an intriguing and complex history that spans over millions of years, whales, both baleen and toothed, hold some unique evolutionary advancements in the scientific world.

With their closest relative being the hippopotamus, whales share the same mammalian traits as all species of the mammal order. Whales have repositioned their nostrils for air-breathing efficiency and have an extended gestation period and parental care. 

Whales do lactate, although it is more the consistency of toothpaste than the milk that you would find in the fridge.

Gray whale

The whale is a descendant of a hoofed mammal from 50 million years ago. The whale has made some extraordinary advancements in its journey back to the water, but some land-based traits have been preserved, making them unique among marine mammals.

Are All Cetaceans Mammals?

Cetacean refers to an order of marine mammals that incorporates 90 species, including 49 species of dolphins (river and oceanic) and porpoises. 

The other 41 species are divided into baleen whales of which there are 14 species and 27 species of toothed whales.

All of these carry the significant mammalian traits of being warm-blooded, having fur, lactating, and breathing air.


Cetaceans belong to the group eutherians as they do not lay eggs or posses pouches, and give birth to live young after an extended gestational period. They then continue parental care with lactation, like land mammals, until their young are independent (Campbell Biology, 2015).

What is a Mammal?

A mammal is a warm-blooded animal with fur (however sparse) and feeds its young milk. They also have lungs, and therefore, must breathe air. When thinking of a mammal, the obvious examples are humans, possibly dogs, and cats. 

However, marine animals such as dolphins, whales, dugongs, and manatees are also classed as mammals as they possess all of these traits.

The order of Mammalia includes animals that possess mammary glands. The order incorporates monotremes (egg-laying mammals) such as echidnas, Marsupials (mammals with pouches) such as kangaroos and possums. The third includes Eutherians, which are also known as placental mammals. Eutherians have a long gestation period, as evidenced by humans carrying their young for nine months.

Next, we look at how whales show these typical mammalian traits.


Do Whales Have Fur?

One of the more subtle features of mammals, with marine mammals, is no exception, is that at some point in their life cycle, they have fur.

This does not necessarily mean that the animals are visibly hairy or even that the adults of mammalian species have visible hair. Most dolphins are born with hairs around their muzzles, which is then lost soon after birth, except the amazon dolphin, which uses these whiskers as sensory organs.

Additionally, bumps that are visible on the backs of humpback whales are hair follicles and can be either active or inactive depending on the individual.

Killer whale breaching (Orcinus orca), Alaska, Southeast Alaska

Hair can be seen on most newborn whales as well as other marine mammals, but the majority of them shed their hair within the first few weeks of life after birth.

Hair is not necessary for whales the way it is for many other mammals such as dogs or cats. Most mammals use their fur to keep warm, but whales have a layer of blubber for this reason.  

Whales having fur is a sign of their evolutionary lineage from furry land-dwelling mammals.

Want to know where you can see whales in North America? Find out in a guide I have written. You can find it here.

Are Whales Warm-blooded?

Cold-blooded fish, including sharks, are ectothermic, meaning that they use their outside temperature to regulate their body temperature. Whales, as part of the mammalian group, are warm-blooded, or endothermic homeotherms. This means that whales must maintain their body temperature using energy that they convert from food.

Whale calf feeding

As whales are so large, there has been some discussion about how whales can take in enough food to produce the required energy for the movement of their huge bodies and to keep them warm. One development is that of baleen, the keratin plates in the larger whales mouths.

These baleen plates allow whales to hunt for their smaller prey much more efficiently by taking in large amounts of water and filtering the small organisms out by pushing the water from their mouth through the baleen. 

In contrast, smaller toothed whales tend to eat larger meals of octopus and, in many cases, seals, which also have a high-fat content due to their thick layer of blubber.


The layer of blubber on seals is also present on whales to assist with insulation, but also as a food store if they are unable to find food for a long period. This food store also aids in migration as whales will build up their fat store for traveling between feeding and mating grounds.

Whales can endure water temperatures as low as -2 Celsius or 28.4 degrees Fahrenheit and air temperatures of -40 degrees Celsius or Fahrenheit (they are the same at this temperature.) Seawater does not freeze at these frigid temperatures due to movement and salinity levels. 

Whales maintain their internal body temperatures by both physiological and behavioral methods. Behaviorally, whales will migrate if they are too cold and often migrate for mating and calving in warmer waters. 

Physiologically, whales are big and preserve heat through a large surface area to volume ratio. This means that there is a low amount of skin compared to their weight in which to lose heat through. 

Gray whale

Hair is less effective in heat preservation in the water, so in the case of marine mammals, it has been replaced by blubber.

Whale Reproduction

As land-mammals do, whales give live birth to calves after an extended gestation period, which lasts between 10 and 17 months, depending on the species.

During this time, as placental mammals, the calf is connected to the mother by an umbilical cord, just like humans. They share blood, which provides the calf with nutrients and also removes waste products, all using the mother’s internal organs.

Calves are born underwater, and whales have developed an interesting adaptation to deal with that. Where young mammals are usually born headfirst and take their first breath as soon as air touches their faces, marine mammals, including whales, give birth tail first. 

This method ensures that the air-breathing calf will not drown if birth takes longer or there are complications. As whale calves are born ready to swim, being born tail first means that they are facing the same direction as the mother.

Gray whale

Once the calf is born, the mother produces milk in a thick paste form with high-fat content, which reduces the risk of the milk dissolving in the water. 

The mother will continue nursing anywhere between six months and two years, depending on the species until the calf is feeding independently. Whales mouths are not flexible enough to latch on to a nipple, so the mother whale has to eject the milk into the calf’s mouth. The calf can curl its tongue in a way that the milk is directed into its mouth and not wasted.

If you want to know more about how whales breastfeed, I have written an article which you can find here.

Do Whales Breathe Air?

Fish take the oxygen out of the water using their gills, but as mammals, whales must breathe air. Whales have lungs instead of gills, and their blowholes are basically repositioned nostrils. 

Baleen whales have two nostrils, where toothed whales only have one. Whales are unable to breathe through their mouths as the trachea is not attached to it, so the blowholes on top of their heads are their only means of oxygen intake. This separation removes the risk of the opening of the airway when food is swallowed underwater.

Whales have developed an exceptionally efficient respiratory system, where they can utilize 90% of the oxygen that they breathe in, in contrast to 15% that humans utilize. 

Whales produce a protein called myoglobin, which allows them to store additional oxygen within their muscles for later use; this is particularly useful for long dives, which for some whales can last hours. All mammals produce myoglobin, but whales can produce much greater amounts in comparison to other mammals.

Due to living in an aquatic environment but needing to breathe air, whales are never actually fully asleep. They are capable of sleeping with one half of their brain while the other stays awake and alert in case they need to breathe or are at risk of attack from predators.

Similarities to Land Mammals

Even after millions of years in the sea, whales still have the same bone structures as land mammals. When studying the bone structure of a whale, it is possible to see that their pectoral fins contain the same bones that would be recognized as hands and finger bones in humans, or foot and digit bones in a hippopotamus, which is their closest living relative.


The tail of a whale is an altered version of the tail of land mammals, and vestigial rear limbs can still be seen. The connection with the hippopotamus, itself, a semi-aquatic mammal, was actually discovered through the similar structure of the ankle bones of hippopotamus and whales.

Ever wanted to know why whales slap their tails on the surface of the water? Find out here.

Although sparse, whales do have thick bristly hairs on their bodies and have continued to breathe air, with the nostrils migrating to the top of the head and repurposed as a blowhole, which can erupt to heights of 30 feet or 10 meters.

Whales have held onto what seems to be a very effective reproductive system and extended parental care, which is rarely seen in marine animals.

Ever wondered why whales come close to the shore? Find out the reason why in this article I have written.


With the characteristics of breathing air through adapted nostrils, having fur at some point in their lifecycles, and feeding their young milk, an aquatic environment does not seem the best habitat. 

However, over millions of years, the ancestors of today’s whales were able to adapt to their aquatic environment, which provided them with an untapped supply of nutrients and the ability to grow to enormous sizes. 

Even though they live in a fully aquatic environment, they are able to utilize the unique properties which allow them to stay members of the mammalian group.

Want to know which whales you can watch in North America. I have written a guide which you can read here.


My Favorite Books On Whales

All of these books can be purchased through Amazon.  If you purchase any of them then I may receive a small commission on any purchases you make.  

Spying on whales: The past, present, and future of Earth’s most awesome creatures

Whales, dolphins and porpoises 

Whales, dolphins and seals:  A field guide 

Guide to whale watching in North America

The illustrated encyclopedia of whales and dolphins

References And Further Reading

Hickman, C., Roberts, L., Keen, S., Eisenhour, D., Larson, A., I’Anson, H. 2014, Integrated Principles of Zoology, McGraw Hill Education, New York

National Geographic 2020, Blue Whale, National Geographic Partners, retrieved 29/01/20, <https://www.nationalgeographic.com/animals/mammals/b/blue-whale/>

Stone, M. 2019, How Much Is A Whale Worth?, National Geographic Partners, Retrieved 01/02/20, <https://www.nationalgeographic.com/environment/2019/09/how-much-is-a-whale-worth/>

Whale and Dolphin Conservation, Facts About Whales, Whale and Dolphin Conservation, retrieved 01/02/20, <https://uk.whales.org/whales-dolphins/facts-about-whales/>

Whale and Dolphin Conservation, Do Whales and Dolphins Have Hair?, Whale and Dolphin Conservation, retrieved 01/02/20, < https://us.whales.org/do-whales-and-dolphin-have-hair/>

Whale Facts 2020, Do Whales Have Hair?, Whalefacts.org, retrieved 1/2/20, <https://www.whalefacts.org/do-whales-have-hair/>

Whale Facts 2020, Are Whales Warm-Blooded?, Whalefacts.org, retrieved 1/2/20, <https://www.whalefacts.org/are-whales-warm-blooded/>

Whale Facts 2020, How Do Whales Reproduce?, Whalefacts.org, retrieved 1/2/20, <https://www.whalefacts.org/how-do-whales-reproduce/>

Ballantyne, C. 2009, How Do Marine Mammals Avoid Freezing to Death?, Scientific American, retrieved 01/02/20, < https://www.scientificamerican.com/article/marine-mammals-cold-avoid-freezing-death/>

Echolls, T. 2017, How Do Whales Mate?, Sciencing, retrieved 1/2/20, <https://sciencing.com/whales-protect-themselves-4566498.html>

Garrod, B. 2020, How Do Whales Breastfeed Underwater?, Discover Wildlife, retrieved 01/02/20, < https://www.discoverwildlife.com/animal-facts/marine-animals/how-do-whales-breastfeed-underwater/>

USCB Scienceline 2015, How Come Whales Can Hold Their Breath Longer Than Most Mammals?, National Science Foundation & USCB School-University Partnership, retrieved 1/2/20, < http://scienceline.ucsb.edu/getkey.php?key=1009>

Whale Facts 2020, How Do Whales Breathe?, Whalefacts.org, retrieved 1/2/20, < https://www.whalefacts.org/how-do-whales-breathe/>

Bryan Harding

Bryan has spent his whole life around animals. While loving all animals, Bryan is especially fond of mammals and has studied and worked with them around the world. Not only does Bryan share his knowledge and experience with our readers, but he also serves as owner, editor, and publisher of North American Mammals.

Recent Content