---
title: "What the sources say about the North American Beaver | AnimalTracks.wiki"
description: "59 claims from the North American Beaver profile, each beside the words of the source that backs it."
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---

# What the sources say about the North American Beaver (*Castor canadensis*)

> 59 claims from the North American Beaver profile, each beside the words of the source that backs it. A "..." marks a cut in a quote and [brackets] an insertion.

Profile: [North American Beaver](https://animaltracks.wiki/animals/north-american-beaver/)

## Beaver. Smithsonian's National Zoo and Conservation Biology Institute.

https://nationalzoo.si.edu/animals/american-beaver

| The page says | The source says |
| :--- | :--- |
| Self-sharpening orange teeth strengthened with iron | Their large, orange incisors grow continuously throughout their lifetime ... These teeth are self-sharpening ... The iron strengthens the enamel |
| dams streams into ponds | Dams reduce stream erosion by forming slow-moving ponds. |
| the largest rodent in North America and the second largest in the world, behind the capybara | North American beavers are the largest rodents in North America and the second largest in the world (South America's capybaras being the heaviest). |
| It weighs 35 to 65 pounds (16 to 30 kilograms) | They weigh between 35 and 65 pounds (16 to 30 kilograms) |
| the heaviest beaver on record weighed 110 pounds (50 kilograms) | with the heaviest beaver on record weighing 110 pounds (50 kilograms) |
| runs 3 to 4 feet (1 to 1.2 meters) long | They are 3 to 4 feet (1 to 1.2 meters) long |
| Beavers typically live 10 to 12 years | North American beavers typically live 10 to 12 years. (note: Smithsonian gives no wild/captive qualifier; ADW's older 'average lifespan of a beaver in the wild is 10 to 20 years' disagrees, and the current Smithsonian page wins) |
| the oldest one on record reached 30 in human care | The oldest on record lived 30 years in human care. |
| A beaver's incisors keep growing throughout its life, and daily use wears them down | These teeth grow continuously throughout its life and are worn down through daily use. |
| Self-sharpening, iron-strengthened incisors that keep growing throughout its life and can cut through a finger-thick sapling in one bite | These teeth grow continuously throughout its life ... These teeth are self-sharpening and can cut a tree the size of a person's finger in a single bite! ... The iron strengthens the enamel (note: 'sapling' (a young tree) stands in for the source's 'a tree the size of a person's finger') |
| Their incisors keep growing throughout their life | These teeth grow continuously throughout its life |
| the outer enamel is loaded with iron | the high amount of iron contained in the enamel, which is the hard outer layer of the teeth |
| which makes the teeth look dark orange and strengthens them, helping stop them cracking or breaking as the beaver gnaws | Beavers' incisors appear dark orange due to the high amount of iron contained in the enamel, which is the hard outer layer of the teeth. The iron strengthens the enamel, helping prevent the teeth from breaking or cracking while the beaver gnaws. (note: 'look' is the source's 'appear', a description of colour rather than a hedge) |
| The iron makes the teeth look dark orange and strengthens the enamel, helping keep them from cracking or breaking while the beaver gnaws | Beavers' incisors appear dark orange due to the high amount of iron contained in the enamel, which is the hard outer layer of the teeth. The iron strengthens the enamel, helping prevent the teeth from breaking or cracking while the beaver gnaws. (note: 'look' is the source's 'appear', a description of colour rather than a hedge) |
| Beaver teeth are self-sharpening | These teeth are self-sharpening |
| a single bite can cut through a sapling as thick as a finger | can cut a tree the size of a person's finger in a single bite! (note: 'sapling' (a young tree) stands in for the source's 'a tree the size of a person's finger') |
| incisors that grow too long to let the back molars meet can lead to starvation | If the incisors become too long, they can prevent the beaver's mouth from closing enough for its grinding molars to meet, which could lead to starvation. |
| If the incisors grow too long to let the back molars meet, though, a beaver can starve | If the incisors become too long, they can prevent the beaver's mouth from closing enough for its grinding molars to meet, which could lead to starvation. |
| Underwater, a see-through nictitating membrane, a kind of built-in swim goggle, slides over each eye | The beaver's eyes have a thin, transparent membrane, called a nictitating membrane, which is pulled over the eyeball for underwater work. (note: 'a kind of built-in swim goggle' is a plain-language gloss for the term, not a claim about eyesight) |
| slides over each eye for underwater work | which is pulled over the eyeball for underwater work |
| valves close its ears | Its ears are external, small and rounded, with valves that also close while submerged |
| valves close a beaver's ears while it is submerged | Its ears are external, small and rounded, with valves that also close while submerged |
| It can swim at up to 6 mph (10 km/h) on webbed hind feet | Their larger hind feet are webbed for swimming ... beavers can swim up to 6 mph (10 kilometers per hour) |
| it can swim at up to 6 mph (10 km/h) | beavers can swim up to 6 mph (10 kilometers per hour) |
| oversized lungs let it stay submerged for up to 15 minutes while traveling over half a mile | Their oversized lungs allow them to stay submerged for up to 15 minutes while traveling over half a mile. |
| Oversized lungs let it stay underwater for up to 15 minutes while traveling over half a mile | Their oversized lungs allow them to stay submerged for up to 15 minutes while traveling over half a mile. |
| A Tail With Four Jobs | The tail is used as a rudder in swimming, as a balance prop while working on land and to signal danger when slapped on the water. Beavers will also store fat in their tails (note: the lead-in counts the four uses the page gives: rudder, balance prop, alarm signal, fat store) |
| A beaver's broad, flat, scaly tail | a broad, flat, scaly tail |
| steers it through the water, props it up while it works on land, and slaps the water as an alarm | The tail is used as a rudder in swimming, as a balance prop while working on land and to signal danger when slapped on the water. |
| an alarm that tells nearby beavers to head for deep water | this alarm signal alerts others in the area to seek refuge in deep water |
| It also stores fat: beavers eat more in the fall so they can live off that fat through winter if food runs out | Beavers will also store fat in their tails, eating more in the fall so they can survive off the fat stored in their tails through winter if food is not available. |
| along with leaves, woody stems, roots and aquatic plants | Beavers are herbivores, eating leaves, woody stems and aquatic plants. (note: roots come from ADW, claimed separately) |
| Their favorite trees for both food and building are poplar, aspen, willow, birch and maple | Their chief building materials are also their preferred foods: poplar, aspen, willow, birch and maple. |
| They build watertight dams of sticks woven with reeds, branches and saplings, caulked with mud | they build watertight dams of sticks woven with reeds, branches and saplings, which are caulked with mud |
| which turn streams into slow-moving ponds | Dams reduce stream erosion by forming slow-moving ponds. |
| Beavers also build dome-like lodges that rise 6.5 feet (2 meters) or more and can reach 39 feet (12 meters) wide | Beavers also build dome-like lodges that rise 6.5 feet (2 meters) or more and can reach widths of 39 feet (12 meters). |
| Often built away from the shore, a lodge forms an island that can only be entered from underwater | Often built away from the shore, these lodges form islands that can only be entered from underwater. |
| walls a third of a meter thick can insulate the chamber inside | The lodge chamber may be 4 feet (1.2 meters) wide and 2 feet (0.6 meters) high, insulated by walls one-third of a meter thick (note: 'can' carries the source's 'may') |
| Beaver fur was once in constant demand for robes, coats and top hats | Beaver fur was in constant demand for robes, coats, clothing trim and top hats (called beavers). |
| Wars, including the French and Indian War, were even fought over access to beaver trapping areas | Wars, including the French and Indian War, were even fought over access to beaver trapping areas. |
| In the early 1800s, beaver pelts were the single most valuable commodity in most of North America | During the early 19th Century, beaver pelts were the single most valuable commodity in most of North America. (note: early 1800s = early 19th century) |
| With trapping totally unregulated well into the 20th century, beavers all but disappeared from most of their original range | With trapping totally unregulated well into the 20th Century, beavers all but disappeared from most of their original range. |
| Now protected from overexploitation, they have reestablished themselves over most of the continent and have even become an agricultural pest in some regions | Now protected from over exploitation, beavers have reestablished themselves over most of the continent and have even become an agricultural pest in some regions. |
| Ponds, lakes, rivers, marshes, streams and wetlands across North America, except the California and Nevada deserts and parts of Utah and Arizona | Beavers are found throughout North America with the exception of the California and Nevada deserts and parts of Utah and Arizona. They live in ponds, lakes, rivers, marshes, streams and adjacent wetland areas. |
| leaves, woody stems | Beavers are herbivores, eating leaves, woody stems and aquatic plants. |
| preferring poplar, aspen, willow, birch and maple | Their chief building materials are also their preferred foods: poplar, aspen, willow, birch and maple. |
| Beavers live in ponds, lakes, rivers, marshes and streams across most of North America | Beavers are found throughout North America with the exception of the California and Nevada deserts and parts of Utah and Arizona. They live in ponds, lakes, rivers, marshes, streams and adjacent wetland areas. (note: 'most of' carries the source's exceptions: the California and Nevada deserts and parts of Utah and Arizona) |
| a builder that weaves sticks, reeds and saplings into watertight dams | they build watertight dams of sticks woven with reeds, branches and saplings, which are caulked with mud |

## Castor canadensis (American beaver). Animal Diversity Web, University of Michigan.

https://animaldiversity.org/accounts/Castor_canadensis/

| The page says | The source says |
| :--- | :--- |
| its nostrils close too | the animal's closable nostrils, closable ears, and transparent eye membranes are for aquatic existence |
| They eat bark and cambium, the soft growing layer just under a tree's bark | Beavers eat bark and cambium (the softer growing tissue under the bark of trees). |
| roots and aquatic plants | They also eat water vegetation, as well as buds, and roots. |
| Bark and cambium | Beavers eat bark and cambium (the softer growing tissue under the bark of trees). |
| roots and aquatic plants | They also eat water vegetation, as well as buds, and roots. |

## Cassola (2016). Castor canadensis. The IUCN Red List of Threatened Species 2016: e.T4003A22187946.

https://doi.org/10.2305/iucn.uk.2016-3.rlts.t4003a22187946.en

| The page says | The source says |
| :--- | :--- |
| The IUCN lists the species as Least Concern | Least Concern |

## Wright, Jones & Flecker (2002). An ecosystem engineer, the beaver, increases species richness at the landscape scale. Oecologia.

https://doi.org/10.1007/s00442-002-0929-1

| The page says | The source says |
| :--- | :--- |
| an ecosystem engineer | ecosystem engineering by beaver leads to the formation of extensive wetland habitat |
| In New York's Adirondack Mountains, beavers create wetlands that can support herbaceous (non-woody) plants found nowhere else along the river | In the central Adirondacks, New York, USA, ecosystem engineering by beaver leads to the formation of extensive wetland habitat capable of supporting herbaceous plant species not found elsewhere in the riparian zone. (note: 'non-woody' defines herbaceous; 'along the river' is a plain-language stand-in for 'the riparian zone') |
| In New York's Adirondack Mountains, beavers create wetlands that can support herbaceous plants found nowhere else along the river | In the central Adirondacks, New York, USA, ecosystem engineering by beaver leads to the formation of extensive wetland habitat capable of supporting herbaceous plant species not found elsewhere in the riparian zone. |
| Counting stretches beavers had changed and stretches they had never occupied, a 2002 study found that beavers raised the number of herbaceous plant species in the riverside zone by more than 33% | beaver increase the number of species of herbaceous plants in the riparian zone by over 33% at a scale that encompasses both beaver-modified patches and patches with no history of beaver occupation (note: 'riverside zone' is a plain-language stand-in for 'riparian zone'; 'stretches they had never occupied' paraphrases 'patches with no history of beaver occupation'; 2002 is the reference's publication year) |
| The researchers call the beaver an ecosystem engineer: an animal that physically reshapes its habitat | Ecosystem engineering - the physical modification of habitats by organisms ... ecosystem engineering by beaver |