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Adaptations: Fur

What is Fur?
Fur, or hair, is a structure made of keratin, a type of protein. It grows from hair follicles in the dermis of the skin, and projects from the epidermis of the skin.

What’s the Difference between Fur and Hair?
There is no difference between the structure of fur and hair. Humans tend to refer to themselves as having “hair” while the other mammals have “fur.” The term “hair” is also used when referring to an animal that has little fur, like an elephant.

What does Fur Look Like?
There are different types of hairs.

Vibrissae, such as whiskers, are used for sensing the environment. Most people are familiar with a dog’s whiskers, but whiskers can be found in other places, too, like the ankle of a squirrel.

Guard hairs serve as protection and keep moisture away.

Underhairs, or down hairs, provide insulation.

Awn hairs are shorter than guard hairs and longer than down hairs.

"Pelage" is a term that refers to the composition of the fur of a mammal: its guard hairs; underfur; and awn hairs.

How does Fur Help Mammals?
Fur provides several benefits for mammals.

Insulation: Fur can keep heat or coolness inside the mammal. Fur can also keep heat or cold from reaching the body of the mammal. The insulation properties help to keep the body temperature of the mammal the same at all times. Aquatic mammals, like the American beaver (Castor canadensis), trap air in their fur to conserve heat by keeping the skin dry. The white-tailed deer (Odocoileus virginianus) has hollow hairs that act as insulation and help this animal float when swimming. Voles may have darker fur in the winter to absorb more heat.

Camouflage: The color of fur can help the mammal blend with its surroundings so that it is harder for other animals to see it. White-tailed deer have different coloration in the fawn and the adult. The fawn rests in forests where the light at the forest floor is dappled. Its white spots present a dappled pattern that help it to remain unseen. When it reaches adulthood, this color pattern is no longer of value. The adult deer has a uniform color pattern.

Warning: The striped skunk (Mephitis mephitis) has black and white fur. There is no other mammal in Illinois that it could be confused with. The skunk has a pair of anal glands that can spray a bad-smelling musk. It uses this spray for defense. If it has time, the skunk will arch its back, raise its tail, stamp its feet and make sounds as a warning. If it doesn’t have time or the warning doesn’t work, then the skunk may spray the musk. The spray can be shot about 10 feet and is long-lasting. The spray can cause nausea, burning and temporary blindness. If an animal has been sprayed by a skunk, it will remember it, and when it sees this color pattern will stay away from the skunk.

Blocking Sunlight: Fur can act as sunscreen for mammals. The thick covering of hairs can help stop sunlight from reaching the skin. 

Sensory Functions: Whiskers are modified hairs that serve as sensors.

Protection: Thick fur can act as protection from attack by predators.

Waterproofing: Water reaching the skin can cool a mammal too much. A thick coating of fur can prevent water from reaching the skin.

Does a Mammal Always have the Same Fur?
All mammal hairs are replaced. Some hairs are continually replaced. Others are replaced in a short period of time (shedding). The same mammal can undergo both processes.

Some fur tends to grow to at the same rate and time and reaches a stopping point (determinate growth). This fur may be replaced in a process known as “shedding.” Shedding is often associated with the type of weather. A heavy coating of fur may not be suitable in hot weather, and a summer coating of fur may not be appropriate in winter.  

What Else Should I Know about It?
A tiny muscle is attached to each hair at the base. The muscle can pull on the hair and make it stand up straight. When all the hairs are standing up at once, they can help the animal trap extra warmth against the body. When you have “goose bumps,” this process is trying to make you warmer.