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5 Reasons Whales Are Mammals

Whales are mammals, but many people think they are fish. Although there are similarities, there are also many differences.

Whales have the typical five mammalian characteristics. Whales breathe oxygen from the air and cannot breathe underwater. Whales also give birth to live young and breastfeed milk to their young. All whales are warm-blooded and are born with a small amount of fur.

Many people have asked me why whales are mammals and not fish. In this article, I look at the differences between fish and whales and the five mammalian characteristics that whales share.


Why Are Whales Mammals?

  • Whales breathe oxygen from the air.
  • Whales give birth to live young.
  • Whales breastfeed their young
  • Whales are warm-blooded
  • Whales have a small amount of fur when born

Whales often swim close to the shore. Find out why here

Why Are Whales Not Fish?

Whales are not classed as fish as they don’t share the same characteristics. Fish use gills for respiration, while whales use lungs and breathe in oxygen from the air, not water. Whales also differ from fish as they are warm-blooded (endothermic), while fish are cold-blooded (ectothermic) and cannot regulate their body temperature.

Fish and whales do share some characteristics. Both have vertebrae and live in water, but the differences see them being classified in two different Orders.

Why Are Whales Not Sharks?

All cetaceans, including whales and dolphins, are mammals, while sharks are called fish. Sharks are ectothermic (cold-blooded), while whales can control their body temperature (warm-blooded.)

Sharks use gills to extract oxygen from the water. In contrast, whales use their lungs to take in oxygen from the air. The main similarities between whales and sharks are that they are both large marine animals and some sharks give birth to live young.

Are All Cetaceans Mammals?

All cetaceans are mammals. Cetaceans are an order of marine mammals that incorporates about 90 species, including 49 species of river and oceanic dolphins and porpoises. The other 41 species are divided into 14 species of baleen whales and 27 species of toothed whales. These carry the mammalian traits of being warm-blooded, having fur, lactating, and breathing air.

Cetaceans belong to the eutherians group as they do not lay eggs or possess 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).

Did you know that whales migrate? Please find out more in this article I wrote.

What is a Mammal?

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

Marine animals such as dolphins, whales, dugongs, and manatees are also considered mammals as they possess all the typical mammal traits.

The order of Mammalia includes animals that possess mammary glands. The ranking incorporates monotremes (egg-laying mammals), such as echidnas and marsupials (mammals with pouches), including kangaroos and possums. The third includes Eutherians, which are also known as placental mammals. Whales are Eutherians and have a long gestation period, as evidenced by blue whales carrying their young for 10-12 months.


Do Whales Have Fur?

One of the more subtle features of whales is that they have fur at some point in their life cycle.

This does not necessarily mean that whales are visibly hairy or that the adults of mammalian species have visible hair.

Humpback whales have bumps that can be seen on their backs. These bumps are hair follicles that can be either active or inactive, depending on the individual. This leads to some whales being hairier than others.

Hair can be seen on most newborn whales and 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 like many other mammals, such as dogs or cats. Most mammals use their fur to keep warm, but whales use a layer of fat to regulate their temperature.  

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

Most dolphins are also born with hairs around their muzzles, which are then lost soon after birth, except the amazon dolphin, which uses whiskers as sensory organs.

Find out how whales evolved in this article I wrote

Are Whales Warm-blooded?

Whales are warm-blooded or endothermic homeotherms. This means that whales must maintain their body temperature using the energy they convert from food.

Cold-blooded fish, including sharks, are ectothermic, meaning they use their outside temperature to regulate their body temperature.

As whales are so large, there has been some discussion about how whales can take in enough food to produce the required energy to keep them warm. Baleen whales use large keratin plates in their mouths to ensure that they take in enough food to provide this.

The baleen plates allow whales to hunt for 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 plates. 

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

The blubber built up from eating fatty food assists not only with insulation but as a food store if they cannot find food for an extended period. This food store also aids migration as whales build their fat store for traveling between feeding and mating grounds.

Whales have excellent senses. Find out more here.

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

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

Because whales are large, they preserve heat through a large surface area to volume ratio. This means that there is a low amount of skin compared to their weight to lose heat. 

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

Gray whale

Do Whales Give Birth To Live Young?

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 many other animals. They share blood, which provides the calf with nutrients and removes waste products using their internal organs.

Calves are born underwater, and whales have developed 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 carried tail first means facing the same direction as the mother.

Do Whales Produce Milk?

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 feeds independeWhales’hales’ mouths are not flexible enough to latch onto a nipple, so the mother whale has to eject the milk in the calf’s mouth. The calf can curl its tongue so that the milk is directed into its mouth and not wasted. If you want to know more about how whales breastfeed underwater, I have written this article.

Do Whales Breathe Oxygen?

Whales must use oxygen from the air to breathe. Whales have lungs, and their blowholes are repositioned on top of their heads to absorb oxygen easily. 

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

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

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, with some whales diving for hours. All mammals produce myoglobin, but whales can have much greater amounts than other mammals.

Due to living in an aquatic environment but needing to breathe air, whales are never fully asleep. They can sleep 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 whale’s bone structure, 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.

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

Although sparse, whales 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 erupts 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, rare in marine animals.

If you are going on a whale-watching trip, it is best to be prepared.  Find out more in this article.


With the characteristics of breathing air through adapted nostrils, having fur at some point in their lifecycles, and feeding their young milk, whales are considered mammals. 

However, over millions of years, their ancestors adapted to their aquatic environment, providing 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 can utilize the unique properties that allow them to stay members of the mammalian group.

If you or someone you know loves whales, check out these great whale gifts on Amazon by clicking here.

My Favorite Books On Whales

All of these books can be purchased through Amazon. 

Spying on whales: The past, present, and future

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., LarsonI’Anson’Anson, H. 2014, Integrated Principles of Zoology, McGraw Hill Education, New York

National Geographic 2020, Blue Whale, National Geographic Partners, retrieved 29/01/20, <>

Stone, M. 2019, How Much Is A Whale Worth? National Geographic Partners, Retrieved 01/02/20, <>

Whale and Dolphin Conservation, Facts About Whales, Whale and Dolphin Conservation, retrieved 01/02/20, <>

Whale and Dolphin Conservation, Do Whales and Dolphins Have Hair?, Whale and Dolphin Conservation, retrieved 01/02/20, <>

Whale Facts 2020, Do Whales Have Hair?,, retrieved 1/2/20, <>

Whale Facts 2020, Are Whales Warm-Blooded?,, retrieved 1/2/20, <>

Whale Facts 2020, How Do Whales Reproduce?,, retrieved 1/2/20, <>

Ballantyne, C. 2009, How Do Marine Mammals Avoid Freezing to Death?, Scientific American, retrieved 01/02/20, <>

Echolls, T. 2017, How Do Whales Mate?, Sciencing, retrieved 1/2/20, <>

Garrod, B. 2020, How Do Whales Breastfeed Underwater?, Discover Wildlife, retrieved 01/02/20, <>

USCB Scienceline 2015, How Can Whales Hold Their Breath Longer Than Most Mammals? National Science Foundation & USCB School-University Partnership, retrieved 1/2/20, <>

Whale Facts 2020, How Do Whales Breathe?,, retrieved 1/2/20, <>