Beaver Natural History
Did you know that Beavers:
- are the largest rodent in North America, the second largest rodent in the world, and New York's State Animal?
- eat aquatic plants, grasses, forbs, and the cambium layer of trees?
- live throughout most of North America and can be found in almost all of the United States and Canada, and parts of northern Mexico?
- build dams to create beaver ponds, lodges to live in, and canals to make collecting food easier?
- live in a colony made up of a pair of adults, one or two babies, and one or two yearlings?
What are Beavers?
The North American beaver is the second largest rodent in the world and the largest rodent found in North America [1,2]. These rodents can weigh up to 60 pounds and can get up to 4 feet in length [1,2]. Beavers have a scaly paddle-like tail, large webbed back feet, and thick brown waterproof fur, all of which helps beavers spend much of their time in water [1,2]. Beavers also have large orange chisel-like incisors that they use to cut down trees and other vegetation [1,2]. These teeth are orange due to the large amount of iron that strengthen them and are constantly growing only to be worn down with use [1,2].
The North American beaver is the second largest rodent in the world and the largest rodent found in North America [1,2]. These rodents can weigh up to 60 pounds and can get up to 4 feet in length [1,2]. Beavers have a scaly paddle-like tail, large webbed back feet, and thick brown waterproof fur, all of which helps beavers spend much of their time in water [1,2]. Beavers also have large orange chisel-like incisors that they use to cut down trees and other vegetation [1,2]. These teeth are orange due to the large amount of iron that strengthen them and are constantly growing only to be worn down with use [1,2].
What do Beavers Eat?
Beavers are considered "choosy generalist herbivores" meaning they can eat most plants but will choose some plants over others [2]. Woody deciduous plants, such as trees, make up a big part of the beaver's diet all year round, especially during cold months when non-woody vegetation isn't available [2,3]. Just like us, beavers have favorite foods except in their case their favorite food happens to be trees! Tree choice varies greatly by region but willow, aspen, and poplar are common favorites [2,3]. Beavers will also eat conifers like spruce, pine, and firs, but usually only do so when other tree species aren't available [2,3]. Beavers also like to eat non-woody plants like grasses and forbs on land and aquatic plants growing in the water of their ponds [2,3]. Beavers will change their diet with the season. They tend to eat lots of non-woody plants during the spring and summer when they are most available and woody plants in the fall and winter once the green plants die or enter winter hibernation [2,3].
Beavers are considered "choosy generalist herbivores" meaning they can eat most plants but will choose some plants over others [2]. Woody deciduous plants, such as trees, make up a big part of the beaver's diet all year round, especially during cold months when non-woody vegetation isn't available [2,3]. Just like us, beavers have favorite foods except in their case their favorite food happens to be trees! Tree choice varies greatly by region but willow, aspen, and poplar are common favorites [2,3]. Beavers will also eat conifers like spruce, pine, and firs, but usually only do so when other tree species aren't available [2,3]. Beavers also like to eat non-woody plants like grasses and forbs on land and aquatic plants growing in the water of their ponds [2,3]. Beavers will change their diet with the season. They tend to eat lots of non-woody plants during the spring and summer when they are most available and woody plants in the fall and winter once the green plants die or enter winter hibernation [2,3].
Where do Beavers Live?
Before Europeans arrived in North America beavers were thought to inhabit much of North America with evidence of beavers being found as far north as the Arctic tundra and as far south as Northern Mexico [3,5]. After Europeans arrived in North America this all changed as beavers were hunted and trapped out of much of their native range [2,3]. Thanks to reintroduction efforts in the early 20th century, beavers have returned to much of their native range with some exceptions in California, Texas, several other states and most of their original Mexican range [2].
Before Europeans arrived in North America beavers were thought to inhabit much of North America with evidence of beavers being found as far north as the Arctic tundra and as far south as Northern Mexico [3,5]. After Europeans arrived in North America this all changed as beavers were hunted and trapped out of much of their native range [2,3]. Thanks to reintroduction efforts in the early 20th century, beavers have returned to much of their native range with some exceptions in California, Texas, several other states and most of their original Mexican range [2].
Since beavers are semi-aquatic mammals they can only be found where water is available [3]. Most bodies of water, such as streams, rivers, lakes, ponds, and even bogs can be used be used as homes by beavers as long as there is enough water flow to supply the area with water year round but not enough water flow to wash away the structures beavers create [2,3]. Since beavers are generalist herbivores, as long as they have a good supply of water they can make do with in most types of vegetation [3]. As long as woody vegetation is available for eating and dam and lodge building beavers can live in most any habitat [3].
How do Beavers Build Dams, Lodges, and Canals?
To begin building a dam, beavers will push mud, rocks, sticks, or leaves across the width of the running body of water in order to raise the level of land in that spot [2,3]. Beavers may also place larger branches across a water body, anchoring them with rocks and grasses [3]. The beavers then build up the height of the dam by pushing leafy sticks, stripped branches, and other materials into the bottom of the body of water or into the dam [2]. More branches are then weaved through the attached branches of the dam in order to widen and strengthen the dam [2]. Finally, the beavers will block up holes in the dam using mud, leaves, and grasses until it is water-tight. Beavers build dams in order to create ponds and lakes which allows them to gain access to more trees and vegetation growing along the banks [2,3].
To begin building a dam, beavers will push mud, rocks, sticks, or leaves across the width of the running body of water in order to raise the level of land in that spot [2,3]. Beavers may also place larger branches across a water body, anchoring them with rocks and grasses [3]. The beavers then build up the height of the dam by pushing leafy sticks, stripped branches, and other materials into the bottom of the body of water or into the dam [2]. More branches are then weaved through the attached branches of the dam in order to widen and strengthen the dam [2]. Finally, the beavers will block up holes in the dam using mud, leaves, and grasses until it is water-tight. Beavers build dams in order to create ponds and lakes which allows them to gain access to more trees and vegetation growing along the banks [2,3].
In order to build a lodge, beavers usually dig a hole into the bank of the pond/lake for temporary shelter ([2,3]. This "bank hole" is then reinforced with branches and logs which creates a "bank lodge" [2,3]. Bank lodges are often used when a lake or pond is too deep to create a "free-standing lodge," a lodge surrounded on all sides by water [2,3]. In order to build a free-standing lodge, the beavers must first build up a platform underwater out of logs and branches that are anchored in the substrate of the pond or lake [2,3]. Once the platform reaches the surface of the water the beavers can continue building the lodge much like they build a bank lodge or dam [2,3]. Whatever type of lodge beavers build, they will cover the structure almost entirely with mud leaving only a uncovered section at the top of the lodge for ventilation and air exchange [2,3]. Most beaver lodges have multiple entrances/exits which allow beavers to enter and exit from any direction [2,3]. Beavers build lodges in order to have a safe place to sleep and rest, mate, raise young, and seek shelter from the cold, heat, or predators [3].
The last piece of infrastructure beavers are known to build are canals. By dredging up sediment from common foraging paths, beavers are able to extend their reach into the forest while still being in the relative safety of water [2,3]. This allows beavers to venture out of their ponds and lakes to collect food and logs used for dam and lodge building/repairs without having to deal with the risk of encountering predators on land [2,3,5].
Do Beavers Live Alone or as a Family?
Beavers live in a family group called a colony. This colony is typically made up of a monogamous pair of parent beavers, one or two yearling beavers, and one or two babies known as kits [2,3]. As the kits grow up and become yearlings and more kits are born, the previous yearlings leave on their own or are expelled by the colony [2,3]. These beavers will then leave the area to find their own mate and build their own dam and lodge [2,3]. In some cases when a beaver lake or pond is particularly large the newly independent beavers will remain in the area and build their own lodge [2,3]. A colony of beavers works together to keep the dam and lodge in working order, clean the inside of the lodge, grooms one another inside the lodge, and collectively helps raise the kits [2,3]. Unlike most rodents, beavers do not have many babies at one time, take care of their babies for a long time, and teach their kits for longer [2].
Beavers live in a family group called a colony. This colony is typically made up of a monogamous pair of parent beavers, one or two yearling beavers, and one or two babies known as kits [2,3]. As the kits grow up and become yearlings and more kits are born, the previous yearlings leave on their own or are expelled by the colony [2,3]. These beavers will then leave the area to find their own mate and build their own dam and lodge [2,3]. In some cases when a beaver lake or pond is particularly large the newly independent beavers will remain in the area and build their own lodge [2,3]. A colony of beavers works together to keep the dam and lodge in working order, clean the inside of the lodge, grooms one another inside the lodge, and collectively helps raise the kits [2,3]. Unlike most rodents, beavers do not have many babies at one time, take care of their babies for a long time, and teach their kits for longer [2].
Since beavers live in groups it is important for them to communicate with one another as well as with other non-family group beavers. For close proximity communication beavers will use vocalizations to communicate with one another. These vocalizations include whines, growls, and hisses [2,3]. Hissing and growling appears to be related to aggression towards other beavers, predators, and humans, or when they smell an unusual smell or are frightened [2,3]. Whining is mostly produced by kits and younger beavers as a way to beg for food or complain when their food is taken by other beavers [2]. In order to communicate over longer distances, beavers will often slap their tails on the surface of the water in order to warn other beavers in the area of predators or simply when they are frightened [2,3]. This often causes the other beavers in the colony to tail slap in return and dive deeper into the water or run to water from land [2,3].
Another way for beavers to communicate with one another is through scent marking. Unlike vocalization, scent marking serves to mark the borders of a colony's territory in order to keep foreign beavers away [2,3]. Beavers of both sexes contain two scent glands, castor glands that produces an brownish paste and anal glands that produces an oily substance [2,3]. Castoreum that is produced in the castor glands and oil from the anal glands are used to scent mark "scent mounds," piles of substrate that beavers will deposit around their territory [2,3]. These scent mounds serve to let other beavers know when they are entering another colony's territory [2,3]. Often, beavers that encounter a scent mound from another beaver they are unfamiliar with will scratch out the scent mound and replace it with their own [2,3]!
Another way for beavers to communicate with one another is through scent marking. Unlike vocalization, scent marking serves to mark the borders of a colony's territory in order to keep foreign beavers away [2,3]. Beavers of both sexes contain two scent glands, castor glands that produces an brownish paste and anal glands that produces an oily substance [2,3]. Castoreum that is produced in the castor glands and oil from the anal glands are used to scent mark "scent mounds," piles of substrate that beavers will deposit around their territory [2,3]. These scent mounds serve to let other beavers know when they are entering another colony's territory [2,3]. Often, beavers that encounter a scent mound from another beaver they are unfamiliar with will scratch out the scent mound and replace it with their own [2,3]!
References
1. North American Beaver, North American Beaver (2016)
2. Baker, B. W., and E. P. Hill. (2003). Beaver (Castor canadensis). Pages 288-310 in G. A. Feldhamer, B. C. Thompson, and J. A. Chapman, editors. Wild Mammals of
North America: Biology, Management, and Conservation. Second Edition. The Johns Hopkins University Press, Baltimore, Maryland, USA
3. Muller-Schwarze, D. (2011). The Beaver : Natural History of a Wetlands Engineer: Vol. 2. ed. Comstock Publishing Associates.
4. Grudzinski, B. P., Cummins, H., & Vang, T. K. (2020). Beaver canals and their environmental effects. Progress in Physical Geography: Earth and
Environment, 44(2), 189–211. https://doi.org/10.1177/0309133319873116
5. Naiman, R. J., Johnston, C. A., & Kelley, J. C. (1988). Alteration of North American Streams by Beaver. BioScience, 38(11), 753–762. doi: 10.2307/1310784
Picture References in Order of Use
Williams, K. [2011]. A Beaver Tale. [Photograph]. Retrieved from https://tinyurl.com/abeavertale
Poskanzer, A. [2010]. Willow. [Photograph]. Retrieved from https://tinyurl.com/yao6yh2y
Allen, N. [2010]. Aspens. [Photograph]. Retrieved from https://tinyurl.com/yaqstufj
di bo di. [2006]. Poplar. [Photograph]. Retrived from https://tinyurl.com/ya8ow62b
Baker, B and Hill, E. [2003]. Distribution of the Beaver (Castor canadensis). [Map]. Retrieved from Beaver (Castor canadensis) page 289
Kelly, T. [2012] Beaver Dam in Autumn. [Photograph]. Retrieved from https://tinyurl.com/beaverdaminautumn
Arthur, A. [2011]. Beaver Lodge on Banks. [Photograph]. Retrieved from https://tinyurl.com/y9ruyetf
Kilby, E. [2009]. Beaver Lodge. [Photograph]. Retrieved from https://tinyurl.com/y895md5v
Natali, J. [2017]. Beaver Canal. [Photograph]. Retrieved from https://tinyurl.com/y8xe7xma
Halsam, E. [2014]. Mother and Child. [Photograph]. Retrieved from https://tinyurl.com/yavy4uf2
Connecticutbirder. [2010]. IMG_3537 Beaver Scent Mound. [Photograph]. Retrieved from https://tinyurl.com/y8y9d2fd
1. North American Beaver, North American Beaver (2016)
2. Baker, B. W., and E. P. Hill. (2003). Beaver (Castor canadensis). Pages 288-310 in G. A. Feldhamer, B. C. Thompson, and J. A. Chapman, editors. Wild Mammals of
North America: Biology, Management, and Conservation. Second Edition. The Johns Hopkins University Press, Baltimore, Maryland, USA
3. Muller-Schwarze, D. (2011). The Beaver : Natural History of a Wetlands Engineer: Vol. 2. ed. Comstock Publishing Associates.
4. Grudzinski, B. P., Cummins, H., & Vang, T. K. (2020). Beaver canals and their environmental effects. Progress in Physical Geography: Earth and
Environment, 44(2), 189–211. https://doi.org/10.1177/0309133319873116
5. Naiman, R. J., Johnston, C. A., & Kelley, J. C. (1988). Alteration of North American Streams by Beaver. BioScience, 38(11), 753–762. doi: 10.2307/1310784
Picture References in Order of Use
Williams, K. [2011]. A Beaver Tale. [Photograph]. Retrieved from https://tinyurl.com/abeavertale
Poskanzer, A. [2010]. Willow. [Photograph]. Retrieved from https://tinyurl.com/yao6yh2y
Allen, N. [2010]. Aspens. [Photograph]. Retrieved from https://tinyurl.com/yaqstufj
di bo di. [2006]. Poplar. [Photograph]. Retrived from https://tinyurl.com/ya8ow62b
Baker, B and Hill, E. [2003]. Distribution of the Beaver (Castor canadensis). [Map]. Retrieved from Beaver (Castor canadensis) page 289
Kelly, T. [2012] Beaver Dam in Autumn. [Photograph]. Retrieved from https://tinyurl.com/beaverdaminautumn
Arthur, A. [2011]. Beaver Lodge on Banks. [Photograph]. Retrieved from https://tinyurl.com/y9ruyetf
Kilby, E. [2009]. Beaver Lodge. [Photograph]. Retrieved from https://tinyurl.com/y895md5v
Natali, J. [2017]. Beaver Canal. [Photograph]. Retrieved from https://tinyurl.com/y8xe7xma
Halsam, E. [2014]. Mother and Child. [Photograph]. Retrieved from https://tinyurl.com/yavy4uf2
Connecticutbirder. [2010]. IMG_3537 Beaver Scent Mound. [Photograph]. Retrieved from https://tinyurl.com/y8y9d2fd