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What the sources say

Eurasian BeaverCastor fiber

Every figure, record and mechanism on the Eurasian Beaver profile was written from a source, and this is the working table behind it: 51 claims checked word for word against these sources. The left column is what the page says. The right column is the source's own words, copied, not paraphrased; a ... marks a cut and[brackets] an insertion. Open any source and check it yourself.

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Source
01

Animal Diversity Web, University of Michigan

Castor fiber (Eurasian beaver). Animal Diversity Web, University of Michigan.

The page saysAn adult weighs 13 to 35 kilograms (29 to 77 pounds) and measures 73 to 135 centimeters (29 to 53 inches) long
The source saysEurasian beavers weigh from 13 to 35 kg and are 73 to 135 cm in length.Note: 13-35 kg converts to 28.63-77.09 lb and 73-135 cm to 28.74-53.15 in, rounded
The page saysAnimal Diversity Web says it can live 10 to 17 years, though in the wild few live past 7 or 8
The source saysEurasian beavers can live 10 to 17 years of age but rarely live longer than 7 to 8 years in the wild.Note: lifespan rests on ADW alone, so it is credited to ADW
The page saysIn winter it eats mostly woody plants, preferring willow, aspen, and birch; in summer it feeds heavily on aquatic plants, shoots, leaves, and roots
The source saysEurasian beavers are herbivores, feeding primarily on woody vegetation in the winter months. Eurasian beavers prefer willow, aspen, and birch trees ... During summer months beavers feed heavily on aquatic vegetation, shoots, twigs, bark, leaves, buds, and roots.
The page saysA beaver's ears and nostrils have valves and its eyes have nictitating membranes, inner eyelids, closing when it goes under water
The source saysBoth ears and nostrils are valvular and the eyes have nictitating membranes, closing when they go under water.Note: 'inner eyelids' glosses nictitating membrane for the audience
The page saysA fold of skin inside its mouth lets it gnaw on branches underwater without getting water in its mouth
The source saysInside the mouth, beavers have a skin fold that allows them to gnaw on branches under water without getting water in their mouths.
The page saysit can stay submerged for 4 to 5 minutes at a time
The source saysBeavers are semi-aquatic and can stay under water for 4 to 5 minutes at a time.
The page saysIts two large incisors carry hard, orange-colored enamel on the front surface
The source saysThey have two, large incisor teeth with hard, orange-colored enamel on the anterior surface.
The page saysTheir dams alter a stream's flow and flood former uplands, and the new water draws in new species of birds, fish, and amphibians
The source saysThrough the process of building dams they alter the flow of the water and flood many acres of former uplands. ... This new water source attracts new species of birds, fish, and amphibians by providing a suitable water table.
The page saysThey live in colonies of up to 12 with one dominant breeding pair
The source saysIn the lodges, beavers live in colonies of up to 12. These colonies consist of only one dominant, monogamous breeding pair.
The page saysmark their territory with castoreum, a pungent scent from glands near the tail
The source saysEurasian beavers have two castoreum glands located next to the cloacal opening. These glands produce a pungent, sweet smelling chemical called castoreum and is used to mark territories.Note: 'near the tail' simplifies 'next to the cloacal opening' for the audience
The page sayswhich they put on mounds of mud piled up on the shore
The source saysThey do this by building a scent mound on the shore. They bring mud and vegetation up from the bottom, holding it tight to their chest with their forelegs and pushing themselves up the bank with their hind legs until they have a mound. The beaver will then apply castoreum to the mud pile creating a scent mound.
The page saysEurasian beavers once lived across Europe and Asia, but overhunting for fur and castoreum, along with habitat loss, left most countries there with none by the 19th century
The source saysEurasian beavers, Castor fiber, once heavily populated all of Europe and Asia. However due to overhunting for fur and castoreum, a chemical from their castor sacs, and habitat loss, populations fell nearly to extinction. By the 19th century most countries in Europe and Asia had no remaining beavers.
The page saysCastoreum is a pungent, sweet-smelling substance made in two glands near the base of a beaver's tail
The source saysEurasian beavers have two castoreum glands located next to the cloacal opening. These glands produce a pungent, sweet smelling chemical called castoreumNote: 'near the base of a beaver's tail' simplifies 'next to the cloacal opening'
The page saysa beaver brings mud and plants up from the bottom, holds them against its chest with its forelegs and pushes itself up the bank with its hind legs until it has a mound, then puts castoreum on the pile
The source saysThey bring mud and vegetation up from the bottom, holding it tight to their chest with their forelegs and pushing themselves up the bank with their hind legs until they have a mound. The beaver will then apply castoreum to the mud pile creating a scent mound.
The page saysTo mark its territory
The source saysEurasian beavers are very territorial and mark their territory with castoreum, a form of olfactory communication. They do this by building a scent mound on the shore.
The page saysA beaver that finds an unfamiliar scent mound in its territory often reacts aggressively, hissing and slapping the water with its tail
The source saysBeavers act very aggressively towards an unknown scent mound in their territory often hissing at it and slapping the water with the tail and resurfacing right away.
The page saysPopulations fell nearly to extinction
The source saysHowever due to overhunting for fur and castoreum, a chemical from their castor sacs, and habitat loss, populations fell nearly to extinction.
The page saysAnimal Diversity Web estimates that by the 20th century about 1,300 Eurasian beavers were left in the wild
The source saysBy the 20th century an estimated 1300 beavers remained in the wild.
The page saysFreshwater rivers, streams, lakes, and ponds, usually in forested areas with willow, aspen, birch, and alder
The source saysEurasian beavers are semi-aquatic and inhabit freshwater systems, including lakes, ponds, rivers, and streams, usually in forested areas but also in marshes and swamps. Permanent access to water is necessary and preferred tree species for C. fiber are willows, aspen, birch, and alder.Note: stats.habitat
The page saysWoody willow, aspen, and birch in winter; aquatic plants, shoots, leaves, and roots in summer
The source saysEurasian beavers are herbivores, feeding primarily on woody vegetation in the winter months. Eurasian beavers prefer willow, aspen, and birch trees ... During summer months beavers feed heavily on aquatic vegetation, shoots, twigs, bark, leaves, buds, and roots.Note: stats.diet
The page saysHard orange-enameled incisors
The source saysThey have two, large incisor teeth with hard, orange-colored enamel on the anterior surface.Note: stats.superpower, part 1
The page saysvalved ears and nostrils that close underwater
The source saysBoth ears and nostrils are valvular and the eyes have nictitating membranes, closing when they go under water.Note: stats.superpower, part 2
The page saysdams that flood former uplands and draw in new birds, fish, and amphibians
The source saysThrough the process of building dams they alter the flow of the water and flood many acres of former uplands. ... This new water source attracts new species of birds, fish, and amphibians by providing a suitable water table.Note: stats.superpower, part 3
The page saysorange-toothed dam builder
The source saysThey have two, large incisor teeth with hard, orange-colored enamel on the anterior surface.Note: tagline; dam building is covered by the body's dam claims
The page saysdangerLevel: Low
The source saysNegative Impacts crop pestNote: task #717; Low is 'Effectively harmless to people'. ADW's negative impacts are flooding, crops and timber, with no 'injures humans' flag (the raccoon's ADW page carries one)
The page saysweightKg: 24
The source saysEurasian beavers weigh from 13 to 35 kgNote: task #717; midpoint of ADW's range. The name guess puts 'beaver' in Light (<10 kg); the whole 13 to 35 kg range is Medium. Not in a curated matchup

Source
02

Gazzard 2024

Gazzard (2024). Castor fiber. The IUCN Red List of Threatened Species 2024: e.T4007A218566456.

The page saysLeast Concern
The source saysIUCN Red List category: Least Concern (LC).

Source
03

Brazier et al. 2020

Brazier et al. (2020). Beaver: Nature's ecosystem engineers. WIREs Water.

The page saysEurasian beavers were long thought to build smaller dams and lodges than North American beavers, but a 2015 study found that under the same conditions the two species build alike
The source saysUntil relatively recently, it was considered that the North American beaver had a tendency to build dams and lodges more frequently and of a greater size than the Eurasian beaver, but it has now been shown by Danilov and Fyodorov ( 2015 ) that, under the same environmental conditions, the building behavior of the two species does not differ.Note: replaces ADW's older 'much smaller dams and lodges', which this 2020 review supersedes
The page saysGreat Britain lost its last wild beavers about 400 years ago
The source saysbeavers were hunted to near extinction and extirpated entirely in countries such as Great Britain (GB) about 400 years ago
The page saysIn recent decades, reintroductions followed by natural spread have returned the species to much of its Eurasian range
The source saysIn recent decades species reintroductions across Europe, followed by natural expansion has led to the return of C. fiber to much of its Eurasian range
The page saysa review published in 2012 put Europe's population at over 1.5 million
The source sayswith a recent review of national population studies, estimating that the C. fiber population in Europe numbers over 1.5 million individuals (Halley et al., 2012 )Note: the estimate is Halley et al. 2012 as cited by Brazier et al.; dated in the text because it is not a current count
The page says1.5 million
The source sayswith a recent review of national population studies, estimating that the C. fiber population in Europe numbers over 1.5 million individuals (Halley et al., 2012 )Note: covers the tagline's 'over 1.5 million across Europe by 2012'
The page says2012
The source sayswith a recent review of national population studies, estimating that the C. fiber population in Europe numbers over 1.5 million individuals (Halley et al., 2012 )Note: year of the review cited for the 1.5 million estimate (body and tagline)
The page sayshunted to near extinction
The source saysIn the Northern hemisphere, beavers were hunted to near extinctionNote: tagline; the review's statement covers beavers in the Northern hemisphere, the body gives the Eurasian detail from ADW

Source
04

Puttock et al. 2017

Puttock et al. (2017). Eurasian beaver activity increases water storage, attenuates flow and mitigates diffuse pollution from intensively-managed grasslands. Science of The Total Environment.

The page saysResearchers introduced two Eurasian beavers to a wooded site on a small stream draining intensively farmed grassland
The source saysTwo Eurasian beavers (Castor fiber) were introduced to a wooded site, situated on a first order tributary, draining from intensively managed grassland.Note: 'small stream' glosses 'first order tributary'
The page saysMainly by building 13 dams, the beavers raised the water stored at the site, with about 1,000 cubic meters held in their ponds, and likely damped storm flows: peak discharges fell by 30% on average
The source saysbeaver activity, primarily via the creation of 13 dams, has increased water storage within the site (holding ca. 1000m 3 in beaver ponds) and beavers were likely to have had a significant flow attenuation impact, as determined from peak discharges (mean 30±19% reduction)
The page saysWater leaving the site carried lower concentrations of suspended sediment, nitrogen, and phosphate
The source saysEvent monitoring of water entering and leaving the site showed lower concentrations of suspended sediment, nitrogen and phosphate leaving the site
The page saystwo beavers released on a small stream draining farmed grassland
The source saysTwo Eurasian beavers (Castor fiber) were introduced to a wooded site, situated on a first order tributary, draining from intensively managed grassland.Note: task #717; vibe.reason; 'small stream' glosses 'first order tributary'
The page saysbuilt 13 dams
The source saysprimarily via the creation of 13 damsNote: task #717; vibe.reason

Source
05

Graf et al. 2015

Graf et al. (2015). The Use of Acceleration to Code for Animal Behaviours; A Case Study in Free-Ranging Eurasian Beavers Castor fiber. PLOS ONE.

The page saysResearchers glued accelerometers, the same kind of motion sensor built into a fitness tracker, to the fur of 12 free-ranging Eurasian beavers in Norway.
The source saysWe deployed tri-axial accelerometer loggers on 12 free-ranging Eurasian beavers Castor fiber in the county of Telemark, NorwayNote: the fitness-tracker comparison is a generic explanation of what an accelerometer is, not a claim from the paper
The page saysResearchers glued accelerometers
The source sayswere attached on the fur of the lower back using two-component epoxy resinNote: epoxy resin is a glue
The page saysA computer model fed the motion data told seven behaviours apart, from swimming and grooming to sleeping
The source sayswe were able to distinguish seven behaviours; standing, walking, swimming, feeding, grooming, diving and sleeping
The page sayswith 95% accuracy
The source saysOur random forests model classified behaviours with 95% accuracy

Source
06

Horn et al. 2011

Horn et al. (2011). Mitochondrial Genomes Reveal Slow Rates of Molecular Evolution and the Timing of Speciation in Beavers (Castor), One of the Largest Rodent Species. PLoS ONE.

The page saysSecond-Largest Rodent on the Planet
The source saysBoth species are characterized by their large body size, being the second largest rodent, and their semi-aquatic lifestyleNote: heading generalizes the body's second-largest-rodent claim, sourced below
The page saysshares the title of the world's second-largest rodent with its North American cousin
The source saysBoth species are characterized by their large body size, being the second largest rodent, and their semi-aquatic lifestyle
The page saysThe beaver family has only two living species, the Eurasian and the North American beaver
The source saystoday the family of beavers, Castoridae, is represented by only two extant species, Castor canadensis in North America and Castor fiber in Eurasia
The page saysa 2011 study of their mitochondrial genomes describes both as the second largest rodent
The source saysBoth species are characterized by their large body size, being the second largest rodent, and their semi-aquatic lifestyleNote: 2011 is the paper's year (reference and 'Collection date 2011'); the title names mitochondrial genomes
The page says2011
The source saysReceived 2010 Jul 13; Accepted 2010 Nov 10; Collection date 2011.Note: the paper's publication year, covers the FAQ's '2011 genetic study' phrasing

Source
07

Ansón & García-Prendes 2024

Ansón & García-Prendes (2024). A beaver in the Tagus river: a new location in Spain. Galemys, Spanish Journal of Mammalogy.

The page saysIn Spain, where new sites have been reported in recent years
The source saysIn recent years, different authors have reported new locations for the species.
The page saysa beaver was sighted in the Tagus river in June 2024 and its presence confirmed from signs on the banks: the first report of the species in that river basin, more than 100 kilometers from the nearest beaver area reported before
The source saysHere we made the first report of the species in the Tagus river basin. The first sighting occurred in June 2024 at dusk, in Zorita de los Canes, Guadalajara ... The presence of beaver in this area was confirmed by visual contact and some signs on the river banks of the Tagus River ... This new locality is more than 100 kilometers from the nearest beaver area reported previously.Note: 'some' qualifies the signs found, not the confirmation

Source
08

Department for Environment, Food & Rural Affairs / Natural England

Approach to beaver management in England. Department for Environment, Food & Rural Affairs / Natural England.

The page saysIn England, the Eurasian beaver is a European protected species, and releasing beavers requires a licence
The source saysIn England, Eurasian beavers are a European protected species under the Conservation of Habitats and Species Regulations 2017. Under the Wildlife and Countryside Act 1981, a licence is required to release beavers in England.Note: page updated 28 February 2025, after the 2022 listing

How the table was made: a writer drafted the profile from these sources and logged each claim with its quote, a reviewer with nothing but this table checked every sentence said no more than its quote, and a script confirmed each quote appears word for word in the source. The method is in the site'sAbout page.