Beaver (Chordate)

By: Puya

Beaver pictures wallpapers images photos | Pictures of Animals
Beaver pictures wallpapers images photos | Pictures of Animals

Classification/Diagnostic Characteristics:
A human provoking a beaver.
A human provoking a beaver.

Beaver are the only remaining members of the family Castoridae. There is only genus Castor, and there are only 2 surviving species; the North American beaver (Castor canadensis) and Eurasian beaver (Castor fiber). Though the two species are extremely similar, [[#|genetic testing]] has suggested that hybridization among the two species may be impossible. They are characterized by the iconic enlarged frontal teeth, webbed hind feet, and thick, flat, scaly, tail. There are some other differences between the two species, mostly based in waeight and body shaped.

Beavers are normally nocturnal, and spend much of their time in the water.

Relationship to Humans
Beavers are the only second to humans in terms of their capacity to influence their ecosystem. They create and maintain wetlands, though human influence, particularly in urban environments, has released a number of pollutants which allow for the spreading of various parasites which effect beavers. In addition, over-hunting for beaver under-fur has drastically reduced the beaver population.
Beaver damns often change water currents, which may result in flooding and subsequent aggression from humans.

Humans have used beavers as resources for various products. In the 18th century, the castoreum was used as a remedy, as it contained salicylic acid, one of the main ingredients of aspirin. Today, people use castoreum in perfumes. Additionally, beaver fur was quite popular and was used to make all articles of clothing, from hats to coats. The beaver was nearly hunted to extinction in the 1600s because of their high demand. (BHu)

Habitat and Niche
Beavers live in the area between land and rivers. They are especially common in streams and rivers, marshes, ponds and shorelines throughout North America, Europe and Asia.
They build domelike homes called lodges that are constructed of branches, small trees, and mud, usually located in the middle of ponds. They also build dams near the banks of lakes and rivers. These dam are famous for blocking up river flow and creating reservoirs. (Fun fact: Because of their ability to build dams, the beaver is commonly labeled the engineer of the animal kingdom and thus is the mascot of MIT)

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Beavers must live around water deep enough to provide aquatic habitat during winter, which is why they congregate around rivers, lakes, and ponds. They are also found in fertile, flat valleys with perennial streams because these regions tend to produce an abundance of food for beavers. They are also found around dense, wooded areas that border lakes. Their dams are made by sticks and stones, plastered together with mud and grass. (BHu)

Predator Avoidance
Interestingly enough, beaver use their dams, not as their homes, but to make ponds in which they make their lodges, which can only be accessed underwater. This makes it nearly impossible for any animal to access the lodges, particularly given that the mud used to stick the sticks together, used like a concrete with the logs serving as rebar, freezes making it hard as stone.
Beavers predominantly rely on thier olfactory sense to determine predator danger, and chose to forage primarily upon aquatic vegetation to spend as little time in away from thier protective dwelling as possible. (GC)
The beaver’s tail can also be used to help ward off predators. When the beaver sense that danger is near it will hit its tail on the ground, thus indicating that a predator is in the area.-
The beaver is also mostly nocturnal which allows them to gather food and build damns without much threat from predators such as foxes and hawks. As a result, beaver do not need many predator avoidance mechanisms, for they have few predators.

The beaver will use the depth of the water created by the dam to avoid its predators, which include, wolves, coyotes, bears, and owls. (Colin Gray)

Nutrient Acquisition
Beavers primarily eat tree as well as the cambium that lies beneath the bark. During the winter the beaver will eat the bark from the inside of their dams, allowing them to avoid hibernation.

Beavers, being strict vegetarians, feed on a variety of [[#|aquatic plants]], including water lilies, and the twigs, leaves, roots, and bark of woody plants, preferring aspen, birch, alder, and willow trees as a source of nourishment. In winter, beavers enjoy consuming the bark and inner bark of trees and shrubs, which is readily available inside of their lodges. In order to gain access to twigs, leaves, and bark, beavers often fell trees, stripping off any edible material and transporting it back to the safety of the water. Upland trails used by beavers usually lead to vital food trees, while trails near the pond typically fill with water to form canals that can be used to float sticks and logs. With the approach of winter, beavers create a stockpile of branches on the bottom of the pond, constructing a cache that they rely on until the onset of spring. (Alexander Soloviev)

Reproduction and Life Cycle/ Growth and Development
Beavers are born in litters of 1-9, averaging at about 4. Both parents help to raise the pups, with children from previous litters occasionally helping. Only about 20%-30% of the kits survive the process to adulthood lasting to their second winter. When spring comes, they will leave their parents lodge and find a mate of their own. Unusually, beavers are monogamous. If one partner dies, the beaver will very rarely find another.
Mating season runs from January to March in the cold regions, and late November or December in the South. The gestation period lasts about 3 months, and once born, baby beavers stay with their parents for about 2 years. They can live to be 20 years old.

Beavers have a soft underfur, for which they were almost hunted to extinction. In addition they have a courser, oily, largely water proof outer coat.

Integument includes info about skin, fur, and nails--The beaver's skin acts as a barrier to chemical and physical attacks from pathogens and helps keep the beaver warm. Under the fur, the beaver's skin consists of two layers, the dermis and epidermis. The epidermis is on the top and has many of its own layers that protect and sustain the body. The dermis is a collection of connective tissue, nerves, blood vessels, and muscles. Under the dermis is where the fatty tissue of the beaver is stored. Link:
The beaver's fur have oil glands in them that prevents water from entering the skin too easily. This is especially useful since beavers spend a lot of time in water and water permiable to the skin was reduce the beaver's speed in water. The beaver has strong claws that helo dig into wood to make their lodges. LInk:

Beavers spend a great deal of time in the water and thus use their webbed hind feet and flat tails to swim quite proficiently. On land, the two species differ slightly. The north American species are capable of bipedial movement, due to their lower center of gravity. Both species however walk primarily on four feet. They waddle on land but used their webbed feet to swim quickly.

The tail of the beaver is unusually broad and covered with scales, which is used like a rudder to maneuver through water. It is also used as a communication tool to slap water with the tail to warn other of danger.
Sensing the Environment
Beavers have excellent senses of smel,l hearing, and touch which they use as their primary method of interacting with the world. They have awful eyesight however.

Beavers have horrible vision because their eyes are small and their vision is not acute. They are near sighted, but it is believed that they are able to see color. While beavers cannot see well above water, an “extra eyelid” called a nictating membrane protects their eyes and enables them to see under water. Since their vision is not good, they rely on other senses to make up for the handicap, such as their sense of smell and hearing. A beaver’s sense of smell is its most important sense, vital for finding food, identifying members of the colony, and detecting strangers and danger. Their nose has a special inner flap that seals out water when they are submerged. There is a special passage from their nose to their throat which connects to the upper lungs. This lets the beaver chew and breath through its nose at the same time, and it can even hold its breath underwater for up to 15 minutes! Also, beaver ears have inner flaps that seal out water when they are swimming. Their ears are small but their hearing is acute. Their oversized auditory canals allow them to pick up sounds and vibrations under water that may indicate danger.
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Gas Exchange
The beaver has the standard mammalian respiratory system, just as humans have. They use lungs to take in oxygen rich air, which diffuses the oxygen into the blood stream. The carbon dioxide in the blood stream is then transferred to the lungs and expelled during exhalation.
In addition beavers have large airtight pouches in their cheeks, which allow them to take in large quantities of air and store it while they carry logs or swim under water.

Beaver Lungs Image: A beaver's lungs and liver allow for more oxygen storage than in any other mammal. When the beaver swims, the valves in its nose and ears are blocked so air can't escape and water can't enter but as soon as the beaver hits the surface, it is able to keep respiring. (

Beaver Lungs

Waste Removal
Beavers method of excreting waste is similar to that of any other mammal. The kidneys filter the blood, and the waste is released as urine. The fecal matter is the remaining, indigestible component of food. Unusually however, Beavers to not have specialized organs for the excretion or fecal matter and urine. Similar to some lizards beavers have a cloaca, which is a single orifice for all waste removal as well as sexual reproduction.

Environmental Physiology (Temperature, Water, and Salt Regulation)

As a mammal, Beavers are able to maintain their homeostasis due to their Endocrine system.
  1. Very large incisor teeth – crucial for felling trees and breaking off small pieces of bark for easier digestion. The incisors get worn down over time but are capable of constantly regrowing. [3]
  2. Very large skull – The large skull allows the beaver to have substantially strong jaw muscles which allow it to chew through even the toughest bark.[3]
Beavers use their tails to help them regulate body temperature. This is because the tail stores fat and helps to release body heat from the beaver. -
The kidneys help them to regulate the water and salt amounts dissolved in their bodily fluids. (Prentice Hall Biology).

Internal Circulation
Beavers have a closed circulatory system, as opposed to the open circulatory system. In an open circulatory system, blood is continually moving through blood vessels and being pumped by the heart.
The heart of a beaver is similar to that of most mammals. The main difference is within the anatomy of the right atrium. The right auricle is divided into 2 ppendages, one for each side of the aorta. The right ventricle is also longer and more narrow than most other mammals. Those differences seem to show similarities between aquatic mammals rather than terrestral mammals. (

Chemical Control (Endocrine System)
The endocrine system of beavers are similar to those of any animal that belongs to the phylogenetic class Mammalia.
Just like other mammals, beavers possess essential organs such as the pituitary gland, hypothalamus, thyroid gland, parathyroid glands, thymus gland, adrenal glands, pancreas, and ovaries and testes (depending on the sex of the animal). These glands all cooperate together to create a functioning endocrine system that operates in nearly the exact same fashion as it does in humans. (2) [GW]

Review Question:
1. How many layers of fur does a beaver have?
2. What is the function and purpose of a beaver dam?
3. There are two parts to the integument of the beaver. Explain these two parts. How has this contributed to the increased possibilities of extinction of beavers?
4. What three senses to beavers primarily use to sense the environment?
5. How can a beavers tail ward off various predators? (Cam Somers)
6. Explain what senses the beaver primarily relies on and how this affects them. (BHu)
7. How do beavers survive without actively getting nutrients throughout hibernation season? (Prashant)

1. Hillis, David M., David Sadava, H. C. Heller, and Mary V. Price. Principles of Life High School Edition. Sudnerland, MA: Sinauer Associates, 2012. Print.