Beaver (Castor Canadensis)
Shwetha Sundar

beaver_457_600x450.jpeg


Classification/Diagnostic Characteristics

Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Rodentia
Family: Castoridae
Genus: Castor

-four incisors and two large front teeth for chipping away at wood
-broad, scaly tail
-water-repellent fur
-webbed hind feet
-poor eyesight, but keen senses of hearing, smelling, and touching
-known for building dams on rivers and stream
-fully separated pulmonary and systemic circuits
-herbivore (primary consumer)
-average life span: up to 24 years
-typical weight: 60 lbs
-alarm signal: slapping broad tail
-are among the largest rodents (2) (KG)


Relationship to humans

Beavers are second to humans in being able to manipulate and change their environment. They create natural dams in areas that humans don't make dams in order to more easily facilitate river flow. However helpful they may be, beavers are still poached for their fur, organs(for medicinal purposes, and meat. Some reservations are created for these beavers to live in their natural habitats undisturbed, but poachers still encroach on their grounds and reduce the population.

Beavers are often found in residential areas near water. Because of this, in many of these areas beavers have destroyed both naturally grown trees and trees that humans have planted. Humans have started to prevent tree damage from beavers in a few ways. First of all, people have made guards out of three foot high wire structures to prevent beavers from getting to the trees. People have also started to spray the base of trees with a mixture of exterior latex paint and mason's sand to try to deter the beaver from gnawing on the wood. (16) (WSS)



Habitat and Niche

The beaver typically lives in a riparian zone, or a stream bed. They work as a key species by creating wetlands for many other organisms to live in. They also create dams and lodges to live in, have easy access to food, and protect themselves from predators such as wolves, coyotes, etc. These lodges and dams consist of trees that the beavers take down and mud. They thatch the mud together with the bark and create a block in the water to live in. Lodges are purposely located in the middle of ponds with underwater entrances and babies, extended family, and young beavers live in them (2) (KG).


Beavers must live around water that is deep enough to provide an aquatic habitat even in the winter. For this reason, they usually congregate near rivers, lakes, and ponds. They are commonly found in areas with steep slopes, although they prefer valleys that are fertile, have a flat terrain, and contain perennial streams. This is because these regions produce an abundance of food for the beavers, and the water source can be dammed to create beaver ponds. (4) (JLev)

Besides living around streams and rivers, beavers are also found to live in dense, wooded areas that border lakes. Their dams are made of sticks and stones, and are plastered together with mud and grass. A typical dam is around five feet or more in height and has at least one underwater tunnel entrance. These beaver dams can last for years.8 (JLau)

Because beavers modify their environments by gnawing down trees and building dams, they greatly affected the local flora. The slow-moving/stagnant water created by their dams allow aquatic vegetation to take root and thrive, and the changing water boundaries causes a swamp-like transition zone to develop between the water and the land. Furthermore, by gnawing trees, beavers allow more light from the sun to reach the forest floor, helping the growth of underbrush. The NPP gained by the growth of the underbrush is typically greater than the NPP lost due to the loss of trees, so beavers generally increase the productivity of the land surrounding their dams and lodges. [1] (FZ)


Beavers building their dam (CC)



Predator Avoidance

In order to avoid predators such as coyotes, wolves, and bears, beavers create dams. Dams are normally used to regulate water flow, but it also serves as a good hiding spot and shield from enemies.

Beavers also make danger signals when they are startled or frightened. The signal is that a beaver will dive while forcefully slapping the water with it's tail, and this loud slapping noise can be heard over large distances, both above and below the water. This serves as a warning sign for other beavers, so if a beaver hears this sound they will often stay underwater for an extended period of time. (5) (PS)

The majority of the beaver's predators are mammalian carnivores who usually cannot swim or not nearly as quickly as the beaver. Beavers are capable of fighting as well and with this combination of fight and or flight beavers are able to avoid predators. Beavers also take preemptive measures in order to not become prey. Beavers frequently stop to sniff and survey the area. (MDS) (20)
A picture of a man who was attacked by a beaver. Shows how ferocious these animals can be
A picture of a man who was attacked by a beaver. Shows how ferocious these animals can be

(mds) [2]
external image b_lodge.jpg
Beaver dam used as protection (CC)


Nutrient Acquisition
Beavers are vegetarians and will not eat anything other than woody or aquatic vegetation. They can eat any kind of wood, although they often prefer alder, aspen, or birch. (11) (AA)
While the two front teeth are used for stripping branches off of trees, the 4 incisors in a beaver's mouth are used for obtaining nutrients. These are the main teeth used for chewing food that the beavers eat, such as aspen bark, sedges, water lilies, pondweed, berries, twigs, and leaves. They only have 4 teeth, so chewing is a little minimum, but the strong gastric juices in the stomach break down the hard factors of the twigs and digestion carries nutrient absorption along. The front (incisor) teeth (which are bright orange) themselves continuously grow throughout the beaver's life. They become stronger and sharpened as the beaver undergoes their everyday use (by cutting trees, chewing, etc.). The beaver's teeth are incredibly important in breaking down food into digestible pieces before digestion occurs, and in therefore also in acquiring nutrients (9) (E.S.S.).
Also important to the beaver diet is cambium, soft tissue under the bark of a tree otherwise known as cork. (1) (SJ)
Because of it's diet, the beaver ends up consuming a lot of cellulose. Because mammals cannot digest cellulose, the beaver has adapted a special digestive system. Inside the beaver stomach, there are bacteria that can digest cellulose. They do so and the beaver then digests the bacteria. This adaptation allows the beaver to eat something most other animals cannot, but it also restricts its habitat to environments suitable for this purpose. (12) (AA)
For nutrients, beavers tend to cut down small trees especially young ones that are growing for the second time. Strategically beavers also cut down trees with broad-leaves because these trees tend to coppice. This means that these trees are able to grow back from their stump which provides the beavers with easy to reach food in subsequent years. This shows the beaver's amazing skill for being able to think about and plan for the future. (19) (BH)

Because Beavers spend so much time in the water and have become adapted to it, they do not have the ability to climb trees. This requires beavers to chew out the base of the tree which can create a dangerous environment if the tree falls! (22)(E.S)



Reproduction and Life Cycle

Beavers mate for life, but if one partner dies, the other will find a new mate. They usually mate at around three years of age. Mating season runs from January to March in colder regions and November to December in warmer regions. The gestation period lasts for about 3 months and kits are delivered once a year. Kits start swimming within 24 hours of their birth and are weaned in two weeks. They can grow up to be about 60 lbs and live up to 24 years.

Each litter usually contains four kits but may have as many as nine. Kits spend most of their time in the lodge so that they are safe from other predators.The young beavers will stay with their parents for two winters before leaving the following spring. Most beavers are sexually mature by their third year at which time they leave, and in some cases, are driven out by their parents to seek mates and territories of their own.[3] (CC)

Review Questions
1. how long is the gestation period for a female beaver?(HSC)




Growth and Development

After mating, female beavers give birth to kits after a gestation period of three months. These kits are weaned and start their own lives away from their parents at about two or three weeks old.

When they are born, beavers weigh about one pound each, and they develop at a rapid rate. There are between two and four newborn beavers in each litter and usually up to ten beavers in a colony. Beavers are able to walk on four feer the day they are born and can swim and explore their habitat soon after. By the time they are completely weaned, beavers weigh about four pounds and are able to eat solid food. Mothers are the primary caretaker during this time as the father maintains the territory. Young beavers are dependent on their mothers for food and for learning life skills by copying their parents' behavior. (13) (JF)




Integument

Beavers have delicate organs inside their body as humans and other mammals do, so it covered by flesh and skin and water resistant hairs that keep it warm and let the beaver cut through water easily. The brown fur on the outside helps repel water and the grey undercoat helps seal in warmth.



Beavers are covered in dark brown fur with lighter fur on its chest and belly. The fur on the beaver is coated in castoreum, and oil secretion from the scent glands, which allows the fur to be waterproof. The waterproof fur allows it to swim faster and live in cooler conditions because the fur dries quickly. Also, below the fur is a very thick layer of fat, which also allows it to stay warm under water. (LC) 18


Movement

Beavers have four legs that they use to move around. They also have webbed hind feet and a broad tail to help propel them through the river water to make quick getaways.

The tail of a beaver has many important properties and functions. For example, in water, the tail is used as a four-way rudder, and on land, the tail props the beaver when it is sitting or standing and is a counter balance when the beaver carries material. A beaver also loudly slaps the water with its tail to create a sound that warns all nearby beavers of impending danger. (10) (MC)

Beavers waddle on land, but in water can swim at speeds up to fives per hour. They can stay underwater for up to fifteen minutes before surfacing. Their eyelids are transparent, functioning like goggles, and their fur is naturally oily and waterproof allowing for good underwater maneuvering. [4] (SM)


Sensing the Environment
The beaver has an extremely keen sense of smell that compensates for its poor eyesight and hearing, allowing it to sense predators, identify relatives, and select the best food to consume. Despite having poor eyesight, their clear eyelids allow them to see underwater while swimming, and their nostrils are shut by valves that keep water from entering the beaver's lungs. (6) (BB-V)

Gas Exchange

Beavers have the same gas exchange methods as humans and other mammals. They have lungs and chambered hearts that exchange oxygen for carbon dioxide. They do swim in water a lot of their life, but they don't have any adaptations for breathing underwater. The beaver uses the expansion and contraction of its diaphram to control the intake and expulsion of air from its lungs. Air passes through the nostrils down the wind pipe and into the lungs where the gasses are taken up groups of alveoli where oxygen is transported into the blood. When the deoxyginated blood passes through the alveolus and becomes oxyginated the blood exchanges carbon dioxide back into the lungs. (DA)


Waste Removal

Beavers have an anus underneath their tails for the excretion of feces.

Because water is abundant for beavers, they excrete urine to dispose of toxic chemicals in their blood, namely nitrogen. In contrast uric acid is the by product of most birds and reptiles, and ammonia is the by product of fish. Urine exits through the urethra of the beaver. (14) (BS)


Environmental Physiology

The grey undercoat of the beaver helps seal in body heat, and the thick brown outer coat reinforces this as well as keeps the chill of the water away from the undercoat.
Beavers waterproof themselves by coating their fur with castoreum, a type of oil from their olfactory (scent) glands. Along with their thick brown outer coat, the beaver has a substantial layer of fat directly under the skin for insulation. (1) (SJ)
The tail stores fat, and because it is nearly hairless, releases body heat, helping the beaver to regulate its body temperature. (10) (MC)

Internal Circulation

The beaver has a closed circulatory like other mammalia (mammals). They have a four chambered heart that separates the levels of blood oxygen concentration from each other. In the first of the two circuits, the pulmonary circuit oxygen depleted blood is pumped from the right side of the heart to the lungs where oxygen diffuses into the blood and carbon dioxide diffuses out of the blood. In the second circuit, the systematic circuit, the newly oxygenated blood then returns to the left side of the heart. There, the heart then pumps the blood again into the systematic capillaries located throughout the body where the blood supplies oxygen and picks up carbon dioxide. Finally the now oxygen depleted blood returns to the right side of the heart where the cycle restarts. (7)(AY)

Chemical Control

The endocrine system of the beaver is that one also belonging to the all rodents. After a stimulus, an endocrine gland will secrete a hormone that will travel to target cells. On the target cell, receptors will recognize the specific hormone and transmit chemical instructions to the cell. The endocrine system, through negative feedback, will control how much hormone is present in the body. For example, in consideration of reproductive activities, estrogen, progesterone and testosterone affect regulation of physical daily activity. (AWC)[5]

Review Questions
1. How do beavers communicate their danger signals with each other?
2. How many layers does a beaver have and what are their functions? (CC)
3. What is the most effective sensory system for a beaver? (DM)
4. Would a beaver make a good pet why or why not? (MDS)
5. Would a beaver be likely to have a countercurrent system due to the amount of time it spends in water seasonally?


References
1. http://www.nhptv.org/natureworks/beaver.htm
2. http://animals.nationalgeographic.com/animals/mammals/beaver/
3. Hillis, David M. Principles of Life. Sunderland, MA: Sinauer Associates, 2012. Print.
4. http://www.bio.umass.edu/biology/conn.river/beaver.html
5. http://a-z-animals.com/animals/beaver/
6. http://fwp.mt.gov/mtoutdoors/HTML/articles/portraits/beaver.htm
7. http://bioserv.fiu.edu/~walterm/human_online/cardio_sys/circulatory_system.htm
8. "Life Of An Animal: The Beaver." Essortment. N.p., n.d. Web. 10 Dec. 2012. <http://www.essortment.com/life-animal-beaver-23564.html>.
9."BEAVERS." Beaver, Castor Canadensis, Damage Management and Control Information. Internet Center for Wildlife Damage Management, 2005. Web. 10 Dec. 2012. <http://icwdm.org/handbook/rodents/beavers.asp>.
10. http://www.landscouncil.org/beaversolution/facts_on_beavers.asp
11. Fall, Samuel. "Beaver Pictures & Facts: Beaver Diet & Reproduction." Beaver Diet & Reproduction. Beaver Pictures and Facts, n.d. Web. 11 Dec. 2012.
12. Graham, Donna. "Beaver." Beaver. South Dakota Department of Game, Fish and Parks, n.d. Web. 12 Dec. 2012.
13. http://bioweb.uwlax.edu/bio203/2010/kinsey_alic/reproduction.htm
14. http://library.med.utah.edu/WebPath/TUTORIAL/URINE/URINE.html
16. http://www.humanesociety.org/animals/beavers/tips/solving_problems_beaver.html
17. http://animals.nationalgeographic.com/animals/mammals/beaver/
18. http://www.nhptv.org/natureworks/beaver.htm
19. http://tinyurl.com/ceyqexa
20. http://fohn.net/beaver-pictures-facts/beaver-fur-predators-behavior.html#Predators
21. http://www.bio.umass.edu/biology/conn.river/beaver.html
22. http://www.gpnc.org/beaver.htm
  1. ^ http://www.wigry.win.pl/bobry/wplyw_en.htm
  2. ^ http://www.nydailynews.com/new-york/scoutmaster-survives-attack-rabid-beaver-delaware-river-calls-horror-movie-article-1.1135473
  3. ^ http://www.bio.umass.edu/biology/conn.river/beaver.html
  4. ^










    http://animals.nationalgeographic.com/animals/mammals/beaver/
  5. ^









    http://www.biolsci.org/v04p0126.htm