15 

Beaver Bruce W. Baker 

Castor canadensis Edward P. Hill 

NOMENCLATURE 

C N. Beaver, North American beaver, Canadian beaver, 

American beaver, el Castor 

S N. Castor canadensis 

S. C. c. acadicus, C. c. baileyi, C. c. belugae, C. c. caecator, 

C. c. canadensis, C. c. carolinensis, C. c. concisor, C. c. duchesnei, C. c. 

frondator, C. c. idoneus, C. c. labradorensis, C. c. leucodontus, C. c. 

mexicanus, C. c. michiganensis, C. c. missouriensis, C. c. pallidus, C. c. 

phaeus, C. c. repentinus, C. c. rostralis, C. c. sagittatus, C. c. shastensis, 

C. c. subauratus, C. c. taylori, and C. c. texensis (Hall 1981) 

Castor canadensis (hereafter beaver) is endemic to North America and is one of two extant species in the genus Castor. Castor fiber 

(hereafter Eurasian beaver) is endemic to Europe and Asia, although 

its current range is severely reduced relative to its historical range. The 

general physical appearance of the two species is similar, but their karyotypes and several cranial and behavioral patterns are distinct (Lavrov 

and Orlov 1973). Multilocus allozyme electrophoresis can distinguish 

C. canadensis from C. fiber using tissue or blood samples from either 

live or dead animals, which makes the technique useful as a management tool for restoration of C. fiber in Europe (Sieber et al. 1999). 

C. c. acadicus, C. c. canadensis, C. c. carolinensis, and C. c. missouriensis are the most widespread subspecies of beaver in North America (Hall 1981); however, reintroductions following extirpation have 

substantially altered pristine geographic variation among subspecies. 

The gene pools of some subspecies have been altered through introductions and subsequent mixing with other subspecies. Some subspecies 

may have disappeared entirely. Because subspecies are difficult to determine even with an animal in hand, subsequent discussions will be 

limited to species. 

Fossil remains of a giant beaver, genus Casteroides, and a number 

of closely related prehistoric mammals also have been found in North 

America (Cahn 1932). The family Castoridae dates to the Oligocene 

and was highly diversified in the Tertiary period in North America 

(Kowalski 1976). The genus Castor dates to the Pleistocene (Garrison 

1967) or late Tertiary (M. Schlosser 1902). 

DISTRIBUTION 

Historical Range. Seton (1929) estimated the beaver population at 

60–400 million before European settlement of North America. Beaver 

occurred throughout the subarctic of mainland Canada below the northern tundra and the mouth of the MacKenzie River in the Northwest Territories (Novakowski 1965). They were widespread in Alaska, except 

along the Arctic Slope from Point Hope east to the Canadian border 

(Hakala 1952). Within the contiguous United States, they occupied 

suitable wetland and riparian habitat from coast to coast, even in the 

arid southwest. They were generally absent from the Florida peninsula 

and parts of southern California and southern Nevada. Although their 

original range in Mexico is difficult to determine, they were present in 

the Colorado River and Rio Grande River (Leopold 1959) as well as 

some coastal streams along the Gulf of Mexico. 

Despite their legendary abundance, most beaver populations were 

decimated by fur trappers during the 1700s and 1800s, primarily to 

support the European fashion for felt hats (Bryce 1904). Large trading 

companies, such as the Hudson Bay Company, employed Europeans and 

Native Americans who supplied furs without regard for method or season of take. Because trappers continually moved to new territory, they 

likely were unaware of their cumulative effects on entire populations. 

In addition, intense harvest likely caused the local destruction of population structures, contributing to regional declines (Ingle-Sidorowicz 

1982). Beaver populations in the eastern United States were largely 

extirpated by fur trappers before 1900. 

Growing public concern over declines in beaver and other wildlife 

populations eventually led to regulations that controlled harvest through 

seasons and methods of take, initiating a continent-wide recovery of 

beaver populations. To supplement natural recovery, during the mid1900s beaver were livetrapped and successfully reintroduced into much 

of their former range, a remarkable achievement of early wildlife managers. Although the area of pristine beaver habitat has been much reduced by human land-use practices, beaver have proved to be highly 

adaptable and occupy a variety of human-made habitats. In addition, 

beaver have been intentionally or accidentally introduced into areas 

outside their original range. Thus, the present range of beaver is a result 

of natural recovery and reintroduction to their original range, introduction and expansion into areas beyond their original range, the limits of 

native habitat as modified by human land uses, and adaptability to new 

human-made habitats such as urban areas, croplands, and areas with 

exotic vegetation. 

Present Range. Beaver populations were estimated at 6–12 million 

by Naiman et al. (1988). Beaver now occupy much of their former 

range in North America, although habitat loss and other causes have 

severely restricted populations in many areas (Fig. 15.1) (Hall 1981; 

Larson and Gunson 1983). For example, since 1834, about 195,000– 

260,000 km2 of wetlands has been converted to agricultural or other use 

in the United States, much of which was likely beaver habitat (Naiman 

et al. 1988). Nonetheless, beaver are remarkably adaptable. They can 

marginally subsist above timberline in mountainous areas; however, 

beaver have been unable to colonize Alaskan or Canadian arctic tundra, perhaps because tundra vegetation lacks essential woody plants 

for winter food and lodge construction or because thick ice limits surface access in winter. Although suitable beaver habitat in Canada has 

been reduced since pre-European settlement, fur harvest records indicate that beaver populations have fully recovered in many areas, perhaps a result of a return to earlier successional stages of forest cover 

(Ingle-Sidorowicz 1982). In the United States, beaver populations have 

continued to increase since major reintroductions ended in the 1950s. 

Populations in southeastern states have grown large enough to become 

a major nuisance to the timber industry and others (Larson and Gunson 

1983). In the Far West, they have been reestablished in the Santa Ana 

and Colorado River systems of southern California. In Mexico, beaver 

may still subsist in some northern areas of Nuevo Leon and Chihuahua 

(Leopold 1959), although populations there likely are marginal (Landin 

1980). 

288 
F 15.1. Distribution of the beaver (Castor canadensis). Modifications of 

the range map by Deems and Pursley (1978) include populations in Mexico, 

southern California, west-central Florida, and Delaware and the absence of 

beaver in the North Slope of Alaska. 

Introductions of beaver in Finland (Lahti and Helminen 1974), 

Asian Kamchatka (Safonov 1979), Argentina (Lizarralde 1993), and 

other locations have resulted in the establishment of viable populations 

beyond their original range in North America. For example, 25 mated 

pairs of beaver were introduced (as a captive population) to Tierra del 

Fuego, Argentina, in 1946 to establish a fur industry. Animals that later 

escaped or were intentionally released resulted in a viable wild population. This population rapidly expanded in the absence of predators 

and other natural population controls, causing a substantial impact on 

native southern beech (Nothofagus) forests (Lizarralde 1993). 

DESCRIPTION 

Beaver are the largest rodents in North America. Most adults weigh 

16–31.5 kg and attain a total length of up to 120 cm. They have heavily 

muscled bodies supported by large bones. Forelegs are shorter than hind 

legs, which results in greater height at the hips than at the shoulders. 

Viewed dorsally, beaver are short and thick, broadest just anterior to the 

hips, and taper gradually toward the nose; a short, thick neck appears 

almost continuous with the shoulders and head. Their most characteristic feature is a dorsoventrally flattened, paddle-like tail, the unfurred 

portion of which in most adults varies from 230 to 323 mm long and 

from 110 to 180 mm wide (Davis 1940). The distal three fourths of 

the tail is covered with black, leathery, uncornified scales (Kowalski 

1976) containing a few scattered, coarse hairs. The caudal vertebrae 

are dorsoventrally flattened, with a complex arrangement of muscles 

and tendons to support the flat tail (Mahoney and Rosenburg 1981). Incisors are generally orangish in color, with the anterior surface in adults 

>5 mm wide, a feature that helps distinguish beaver damage from other 

rodent damage on the basis of toothmark width. 

Beaver move with an awkward waddle on land, but can gallop if 

frightened. Adult beaver can walk upright in a bipedal fashion (partially supported by the tail) while carrying mud or sticks held against 

the chest with their chin and front legs. In water, they swim by alternate 

kicks of the hind legs, appearing graceful and efficient, though slow 

and deliberate. Beaver are shaped more like marine mammals than like 

other terrestrial mammals, with a fineness ratio (a hydrodynamic index of streamlining) of 4.8, a value similar to that for phocid seals 

their mouth and to rotate small, pencil-sized stems as they gnaw off bark. 

The ears are rounded, short (30 mm), fleshy, and placed high on the rear 

of the head. The small eyes also are located high on the head, about 

midway between the nose and the base of the skull. Both these adaptations enable beaver to swim with minimum exposure above the water 

surface. 

Pelt coloration is variable within and among populations, with 

reddish, chestnut, nearly black, and yellowish-brown specimens possible in the same watershed. Fur of the flanks, abdomen, and cheeks 

is usually shorter and lighter than back fur. Guard hairs are about 10 

times the diameter of the hairs constituting the underfur, giving the pelt 

a coarse appearance. Guard hairs attain their greatest length (50 mm) 

and density along the back. Underfur is longest on the back (25 mm) 

and has wavy individual hairs, which give the pelt a downy softness. It 

may be dark gray to chestnut in color on the back and, like the guard 

hair, becomes lighter in color on the sides and ventral areas. Unlike the 

case in many furbearers, coloration of individual guard hairs is usually 

consistent throughout their length. 

The two inside (medial) toes of each hind foot have movable, split 

nails, which beaver use as combs to groom their fur (Wilsson 1971). 

Beaver have closable nostrils, valvular ears, nictitating eye membranes, 

and lips that close behind large incisors, adaptions important to their 

semiaquatic existence. During periods of active lactation and when parturition is near, four pectoral mammae are discernible on the chest of 

the adult female. During pregnancy, beaver have a subplacenta located 

between the placenta and uterine tissues. Although its morphology has 

been well described, its function is unknown (Fischer 1985). The reproductive organs of both sexes are internal and lie anterior to a common 

anal cloaca containing the castor and anal glands (Svendsen 1978). A 

notable characteristic of beaver is the strong aroma from the paired 

castor glands. Contents of the castor glands (castoreum) and anal gland 

secretion may be deposited during scent marking. Castoreum has been 

used as a base aroma in perfume and in making trappers’s lures. 

Beaver skeletons are massive when compared to those of other 

mammals of similar length. The skull and the mandible are thick and 

heavy, providing a strong foundation for large incisors (Fig. 15.2). A 

less rugged skull would be unable to withstand the physical stress and 

strain of jaw muscle contractions of sufficient strength to cut hardwoods 

such as oak (Quercus spp.) and maple (Acer spp.). The braincase is 

narrow and there is a small infraorbital canal. A prominent rostrum 

is anterior to the massive zygomatic arch. Adult skulls are very large 

(120–148 mm condylobasal length), which minimizes the possibility 

of confusing them with other North American rodents. Juvenile skulls 

are smaller and may be similar in size to those of adult nutria (Myocastor coypus), porcupine (Erethizon dorsatum), or mountain beaver 

(Aplodontia rufa); however, differences other than size are apparent on 

close examination. As in other semiaquatic mammals, the acetabulum 

is shifted dorsally (Kowalski 1976). The male beaver has a baculum that 

generally enlarges with age (Friley 1949) and can be palpated as an aid 

in determining the sex of live beavers and unskinned carcasses (Denney 

1952). Osteological changes during growth and development of beaver 

were described by Robertson and Shadle (1954). The dental formula is 

I 1/1, C 0/0, P 1/1, M 3/3. Incisors grow continuously and the chiseled 

edge is sharpened by grinding the uppers against the lowers (Wilsson 

1971). The hard enameled front surface of incisors serves as the cutting 

edge to fell trees and peel bark. Cheek teeth are hypsodont and grow 

only through the deposition of cementum at the root base. Deciduous 

premolars are replaced at about 11 months of age by permanent premolars. Specializations such as large size; type and location of ears, 

eyes, and nose; size and function of front and hind legs; and a large, 

flattened tail appear to have individually and collectively enhanced the 

adaptability and survival of beaver in wetland environments. 
F 15.2. Skull of the beaver (Castor canadensis). From top to bottom: 

lateral view of cranium, lateral view of mandible, dorsal view of cranium, 

ventral view of cranium, dorsal view of mandible. 

PHYSIOLOGY 

Growth. Size of the adult beaver depends on latitude, climate, quality 

of available food, and extent of exploitation. In Alabama, a sample of 

1450 beaver from an unexploited population showed mean body weight 

stabilized at 4 or 5 years of age and then diminished slightly after 9 years 

of age. Average weight of all specimens was 18.6 kg; maximum was 

beaver, winter ice formation on ponds and streams restricts or eliminates 

access to surface food, and adults and yearlings lose weight as fat stores 

are depleted. In southern beaver, adults and yearlings also lose weight 

in winter, even though their habitat typically remains ice free. Failure to 

maintain fat reserves during winter for beaver living in ice-free regions 

is likely not due to lack of adequate energy from available food, as it 

may be in the northern range, but instead may be associated with seasonal changes in physiology. Reduced food consumption, as described 

for captive beaver of a northern population, may also occur in southern 

beaver with the onset of warming trends in February and March, as 

beaver are frequently observed sunning themselves on lodges during 

clear sunny days of late winter, and early spring (review by Hill 1982). 

In northern populations, Smith and Jenkins (1997) found that winter loss of body weight and tail size can vary among colonies by severity 

of winter, and sex and age composition of the colony. Beaver lost more 

body weight and tail size when winters were longer. Adults and yearlings that overwintered with young in the colony lost more weight than 

those without young. This supports Novakowski’s (1965) conclusion 

that older members of the colony eat less stored food when young are 

present, and rely instead on other adaptations to survive the winter. 

Thermoregulation. Northern populations of beaver in winter must 

contend with the thermoregulatory cost of foraging under the ice in 

near-freezing water and must subsist primarily on stored food and metabolized fat (Dyck and MacArthur 1992). Some mammals can conserve energy in winter by reducing their body temperature through 

seasonal torpor. Researchers have suspected torpor in beaver, but studies of change in body temperature in response to freezing ambient 

temperatures have been equivocal. Dyck and MacArthur (1992:1671) 

found the body temperature of free-ranging beaver averaged about 37◦ C 

throughout the year, with “no evidence of shallow torpor in either kits 

or adults.” In contrast, D. W. Smith et al. (1991) found the mean daily 

body temperature of adult beaver declined by 1◦ C from fall to winter, but remained constant for kits. Body temperature can also vary 

by daily activity level. Before freeze-up, body temperature is higher 

during daylight hours, when beaver spend more time in the lodge, and 

lower at night, when they are away from the lodge (Dyck and MacArthur 

1992). Thus, thermoregulation likely contributes to overwinter survival 

in beaver in combination with several other adaptations described in this 

chapter, including warmer winter fur, increased body fat, a stored food 

cache, a warmer microclimate in the lodge, huddling together in the 

lodge, and reduced activity in winter (D. W. Smith et al. 1991). 

Digestion. Beaver are hind-gut fermenters. Digestion is enhanced by 

a prominent and unusual cardiogastric gland on the lesser curvature 

of the stomach (Vispo and Hume 1995), a glandular digestive area 

(Kowalski 1976), and a large trilobed cecum containing commensal 

microbiota. Beaver consume a high percentage of cellulose, but maximize the nutritional value of woody plants by eating only the bark. They 

can digest about 32% of available cellulose by microbial action in the 

cecum, which is similar to the case in some other mammals (review by 

Hill 1982, Buech 1984). Beaver have a relatively long small intestine, 

70% longer than in the porcupine, which suggests a high absorptive capacity (Vispo and Hume 1995). Consumption of soft green excrement 

directly from the cloaca (coprophagy) occurs diurnally in the beaver 

(observed as early as 10 days of age; Buech 1984) as well as in the 

Eurasian beaver (Wilsson 1971), lagomorphs, and other rodents. Feces 

are reingested and chewed by the beaver and pass quickly through the 

digestive system (Buech 1984). In contrast, lagomorphs reingest and 

swallow mucous-covered entire pellets. 

Circulation. Beaver heart weight averages 0.40% of body weight, 

which is consistent with heart ratios for other terrestrial mammals, but 
(review by Hill 1982). Aleksiuk (1970a:145) noted that “minute blood 

vessels permeate the entire tail, and a countercurrent heat exchange system is present at the base.” This specialized circulatory feature helps 

conserve heat energy in extremely cold water and radiate heat during 

hot weather. 

REPRODUCTION AND DEVELOPMENT 

Sexual Maturity. Beaver reach sexual maturity (defined as age at 

breeding that results in the first litter) at 1.5–3 years of age, although 

puberty may be reached several months before first breeding. Most 

studies have found at least some beaver had reached sexual maturity 

as yearlings (1.5–2.0 years old), although regional variation is evident. 

Gunson (1970) estimated that two thirds to three fourths of 2-yearold beaver produced young, and believed that early sexual maturity 

in Saskatchewan beaver was enhanced by high-quality habitat. Reproduction in yearlings may cease where >40% of suitable beaver habitat 

is occupied by established colonies. In Newfoundland, 24% of yearling females had bred (Payne 1975). In northern Canada, Novakowski 

(1965) found first pregnancies in 3 of 21 females that were approaching their third birthday, but no indications of conception in females that 

were almost 2 years old. In Alabama, in 2.5- to 3-year-old females, 

only 16 of 65 had ovulated, and there were no indications of ovulation 

or pregnancy in 50 yearlings. However, in Tennessee, Lizotte (1994) 

found sexual maturity occurred at 1.5–2.0 years of age, with a 25% 

pregnancy rate in this age class. 

Breeding. Beaver are monogamous, described by Svendsen 

(1989:339) as “characterized by a single adult pair and young 

forming a family, a relatively long pair-bond where desertion of a 

mate is rare, and turnover of mates usually occurs after the death of 

one of the pair.” Beaver typically breed in winter and give birth in late 

spring, producing only 1 litter/year. The potential breeding season is 

very long, with conception reported between November and March 

and parturition between February and November (review by Wigley 

et al. 1983). Latitude and climate can affect the breeding season, 

which is generally shorter in colder climates and longer in warmer 

climates (Hill 1982; Wigley et al. 1983). Breeding takes place in 

water (Kowalski 1976), bank dens, or lodges. Wilsson (1971) reported 

that C. fiber remains in estrus 10–12 hr and has a second estrus in 

14 days if not fertilized. A gestation period of 100 days is typical for 

C. canadensis (Wigley et al. 1983), with a range of 98–111 days 

(review by Hill 1982). 

Sex Ratios. Sex ratios in monogamous species are important because 

they can influence pregnancy rates. When averaged across age class, 

region, and harvest level, the sex ratio of beaver may be nearly even, 

but substantial variation among populations suggests caution in making this assumption. Sex ratios of trapped populations may reflect bias 

inherent in trapping methods, although results of different studies are 

inconsistent. For example, some studies found no difference in susceptibility of sexes to baited Conibear traps set under ice, but others 

suggested trapping was selective for adult females. Others have noted 

higher mortality from trapping and other causes for adult males (review 

by Hill 1982). In a review of 15 studies, Woodward (1977) found an 

average sex ratio of 98.5 males:100 females, but a ratio of 90.7:100 for 

adults and 111.4:100 for subadults. The combined average from studies 

in Saskatchewan, Newfoundland, Vermont, and Alabama was 105:100 

(N = 4867) (review by Hill 1982). 

Pregnancy Rates. Knowledge of pregnancy rates among age groups 

in monogamous species increases accuracy in computing estimates 

of reproductive performance. Pregnancy rates usually increase from 

calculate reproductive performance. 

Reproductive Performance. Placental scar counts (Hodgdon 1949), 

counts of developing embryos, and, with some limitations, counts of 

corpora lutea and corpora albicantia are useful indices of reproductive 

performance in beaver (Provost 1958). In Mississippi, counts of fetuses, placental scars, and corpora lutea all yielded statistically similar 

estimates of litter size, despite pre- or postimplantation losses (Wigley 

et al. 1984). Preimplantation losses from unfertilized ova or failure 

of fertilized ova to implant and postimplantation losses resulting in resorptions account for differences between ovulation rates and litter size. 

Intrauterine mortality was 16% in 48 beaver from Ohio and almost 19% 

in 40 beaver from western Massachusetts (review by Hill 1982). Where 

rates of prenatal loss are high, correction factors should be developed 

to obtain more precise estimates of litter size and annual productivity 

(Wigley et al. 1984). 

In areas where carcasses are available from fall or early winter 

trapping, counts of placental scars and persisting corpora albicantia, 

corrected for current resorption rates and prenatal loss, respectively, 

provide an index of litter size from the previous spring. Sources of error, such as regression or discoloration of implantation sites by some 

preservatives and degeneration of corpora albicantia with the onset of 

the breeding season (Provost 1962), make estimates of reproductive performance in fall less accurate than those made at other times. Where 

trapping seasons overlap the breeding season, a combination of placental scar counts corrected for the past season resorption rates and 

corpora lutea counts corrected for current resorption rates can provide 

information on litter size. However, early in gestation, it is difficult to 

distinguish between corpora lutea of ovulation and corpora lutea of 

pregnancy, which introduces a potential source of error in estimates 

of reproductive performance (Provost 1962). Also, embryo counts and 

ovulation rates of females trapped in January and February may not 

provide precise estimates of current-year breeding among yearlings 

and subadults. These age groups may breed later than adults (Grinnell 

et al. 1937), particularly at southern latitudes or if they had dispersed 

during the summer. Thus, winter samples may not reflect reproductive 

performance as well as those from May or June. 

Where trapping seasons occur after the breeding season, counts 

of developing embryos, corrected for current resorption rates, provide 

an accurate index of litter size among age groups. Resorption is negligible if embryos are in an advanced stage of development. Where 

possible, delaying the trapping season until breeding has occurred may 

lower the incidence of unbred females whose mates were trapped from 

the population before breeding (Hodgdon and Hunt 1953). Such delay also facilitates measurement of current litter size through embryo 

counts. 

The litter size of beaver is typically two to four, although local 

averages may be as high as six, and the number can vary from one to 

nine (reviews by Hill 1982; Wigley et al. 1983). These reviews suggest 

that beaver in the southeastern United States tend to have smaller litters, 

whereas northern and perhaps western beaver tend to have larger litters. 

Large litters may be associated with better quality habitats and increased 

weight of the mother. In Mississippi, age of mother was only weakly 

correlated with litter size, but weight of mother was strongly correlated. 

Litter size can also be reduced by lack of food (e.g., due to ice on ponds) 

or quality of food (e.g., limited supply of preferred plants) (Rutherford 

1955). Because fewer yearlings breed in relatively dense populations 

and litter size may be inversely related to the number of beaver in 

the family, reproduction in beaver may be density dependent (Payne 

1984). Some evidence also suggests that beaver may breed only during 

alternate years in very poor quality habitat, although this hypothesis 

needs further investigation (D. W. Smith, pers. commun., 2001). 
ontogeny of behavior in captive kits and found they were able to swim 

at 4 days and could dive and stay submerged at 2 months of age. Bipedal 

walking was noted at 1 month of age, and carrying construction materials while walking on the hind legs occurred at 90 days of age. Suckling 

peaked at 25 ml of milk/day at 1 month and decreased until weaned 

at 45–50 days. Zurowski et al. (1974) noted that the anterior nipples 

produced 50–75% less milk than the posterior nipples. Kits can take 

some solid food at 1–4 weeks of age and switch to mostly solid food 

by 1 month. However, they may suckle for up to 3 months even though 

they obtain little milk, perhaps to maintain the mother–infant bond. 

The fur of kits is not water repellent at birth, but after 3–4 weeks of age 

they begin to spread anal gland secretions on their fur, which creates 

water repellency by 5–8 weeks. Captive kits began to dive underwater 

in response to alarm at 8–10 days of age and initiated tail slapping in 

response to alarm at 3–4 weeks of age (Lancia and Hodgdon 1983). 

Rudimentary scent marking began at 13–14 days of age. Thus, very 

young kits express some adult behaviors, but require a long period in 

the family to develop their complex construction ability and other skills 

required for independent life. 

BEHAVIOR 

Social Organization. Individual beaver spend most of their lives in 

small, closed, extended-family units traditionally called colonies. Although the term “colony” is commonly used for beaver, its use has been 

questioned (Hodgdon and Lancia 1983) because a colony more often 

describes a spatially associated collection of individual families rather 

than a single family unit. For example, a family of prairie dogs (Cynomys spp.) living in the same burrow system is called a coterie and a 

group of families is called a colony. However, to maintain consistency 

with previous beaver literature, we use colony to represent an extended 

beaver family. Thus, a beaver colony typically contains the adult pair; 

young of the current year, or kits (<12 months old); and young of the 

previous year, or yearlings (12–24 months old). Sometimes older young 

may remain with the colony as subadults (>24 months old) before they 

disperse, especially if the available habitat is near carrying capacity 

(Busher 1987). A small percentage of colonies may contain more than 

one adult male or female (Busher 1983). Established colonies inhabit 

discrete and defended territories. Dispersing beaver of both sexes, also 

called floaters, remain transient until they settle with an unpaired beaver 

or they build dams or lodges, which may help attract a mate. Compared 

to many other mammals, especially other rodents, beaver populations 

are characterized by relatively low natality, low mortality of young, prolonged behavioral development, high parental care, and adult longevity 

(Hodgdon and Lancia 1983). 

Social interactions involving close contact are fairly infrequent 

outside the lodge, perhaps an adaptation to minimize predation risk on 

land. The most common interaction among individual beaver concerns 

food items and usually involves kits begging for food from older siblings 

or adults (Busher 1983). Adults discourage yearlings from begging by 

snapping their head toward the yearling. Grooming fur to maintain water repellency is a common activity inside the lodge. Beaver groom 

themselves wherever they can reach, but rely on other family members to groom their back fur (Patenaude and Bovet 1984). This social 

grooming appears to be primarily to maintain a layer of air in the fur, 

as does self-grooming, rather than to maintain social bonds or as an 

appeasement gesture (Brady and Svendsen 1981). Aggressive interactions are rare among family members, with most aggression directed 

as threats that do not result in fights. Studies of dominance hierarchy 

systems in beaver have been equivocal. Hodgdon and Larson (1973) described dominance hierarchy as age class (older dominant over younger) 

and sexual (adult females dominant over adult males). Busher (1983), 

)q

repeated in rapid succession. Beaver of all ages whine, but kits account 

for two thirds of events, either when food is at risk of being taken away or 

when begging for food. Food begging by kits is usually effective, which 

provides kits with food without the risk of obtaining it from land (Brady 

and Svendsen 1981; Hodgdon and Lancia 1983). Vocalizations are also 

used to initiate grooming and play. Although beaver are typically docile 

with humans, they sometimes become aggressive, a behavior sometimes 

preceded by a hiss or a growl. 

Probably the most familiar sound produced by beaver is the tail 

slap. The sound is made when a beaver forcefully strikes the water 

with its heavy paddle-like tail, a behavior that may precede diving underwater when alarmed (tail-slap dive). Tail slapping may function to 

(1) issue a warning signal to family members, which typically respond 

by moving to deep water or to the lodge (especially kits); (2) drive away 

potential predators; and (3) elicit a response from the source of disturbance (Brady and Svendsen 1981; Hodgdon and Lancia 1983). Tail 

slapping is used by all ages and both sexes, but studies of variation in 

frequency of use by sex and age have been equivocal. Hodgdon (1978) 

found older beaver slapped more often than younger ones, females were 

more easily provoked than males, and males slapped more times per 

event than females. Sudden alarm often elicits immediate tail slapping. 

However, if beaver are unsure, they often move to deep water and orient toward the disturbance with their nose in the air, a behavior that 

often precedes tail slapping. Smell, sound, sight, and movement are all 

important stimuli, either separately or in combination. The response of 

individual beaver to tail slapping also varies by age. Tail slapping by 

adults elicits the most response from all age classes, but adult beaver 

are the most responsive to tail slapping of other beaver. Kits are least 

likely to move or to elicit a response and yearlings are intermediate 

(Hodgdon and Lancia 1983). 

Scent Marking. Scent marking is a highly developed communication 

method in beaver. Castor glands produce castoreum, a strong-smelling, 

urine-based brown paste containing phenolic, neutral, basic, and acidic 

compounds. Anal glands (also called oil glands) produce anal gland secretions consisting of waxy esters and fatty acids. Castoreum is likely 

derived from diet and thus subject to seasonal variation in odor; however, anal gland secretions are unique chemical identifiers of individual 

beaver (Sun and Muller-Schwarze 1998). Beaver use castoreum and 

anal gland secretions as scent marks, which they actively deposit on 

piles of mud and debris called scent mounds. Beaver deposit castoreum 

by rubbing it on scent mounds during and after construction; it is not 

clear how and when anal gland secretion is applied (Svendsen 1980a). 

Most scent mounds are constructed by adult males, who gather material in their forepaws and carry it to scent mounds in a bipedal fashion. 

Large numbers of scent mounds (>100) can be constructed within a 

territory, and they are usually placed on or near lodges, dams, and trails 

<1 m from water. Beaver of all ages place scent on mounds, but the 

frequency of marking increases with age. Males of all ages place the 

most scent marks (Hodgdon and Lancia 1983). In colder climates, construction and marking of scent mounds peaks soon after ice melts in 

the spring as beaver reoccupy their full territory and reapply scent that 

faded during the winter. In warmer, ice-free regions, scent marking can 

occur all year, but still may be more intense during the spring dispersal 

period. Scent marking has been observed in December and January in 

Alabama, where mounds can reach 35.5 cm in height. 

The primary function of scent marking appears to be territorial. 

Scent marks may define the location and limits of the territory by 

creating a “scent fence” (Muller-Schwarze and Heckman 1980), which 

minimizes aggressive encounters with neighbors and discourages colonization by dispersing beaver. Beaver can distinguish the scent of castor fluid among family members, neighbors, and nonneighbors (beaver 
applied by trappers (Brady and Svendsen 1981). In New York, beaver 

obliterated foreign scent by pawing the mud, overmarking foreign scent, 

and transferring the mud to their own scent mounds (Muller-Schwarze 

et al. 1983). In addition, a territorial function for scent mounds may 

be expressed as a change in the motivational state of beaver. Svendsen 

(1980a) suggested that scent may increase the confidence of resident 

beaver, which smell their own scent, and decrease the confidence of 

nonresident dispersing beaver, thus increasing the likelihood nonresidents will flee a territory “defended” by scent mounds. Experimental 

field studies support a territorial function for scent marking, as Schulte 

(1998) found that beaver could distinguish among the scents of adjacent 

neighbors, far neighbors, and family members. Beaver spent more time 

investigating and overmarking scent from unrelated beaver than from 

family members. 

The ability of beaver to recognize relatives from nonrelatives via 

anal gland secretions (but not castoreum) may help prevent inbreeding 

as related individuals meet each other following dispersal outside their 

home territory (Sun and Muller-Schwarze 1997). Experimental comparisons of compounds in anal gland secretions have not yet clearly 

identified underlying mechanisms, but have shown that perhaps as few 

as two or three compounds may be important in communicating family membership (Sun and Muller-Schwarze 1998). In addition, scent 

marking may help orient beaver within their territory at night, although 

this has not been experimentally demonstrated. 

Scent marking by beaver may be density dependent and vary by 

season and location. In Maine, beaver colonies with close neighbors 

had more scent mounds than isolated colonies (Muller-Schwarze and 

Heckman 1980). In South Carolina, scent marking was positively correlated with colony density. Peak scent marking occurred in fall and 

winter, with very little marking activity in summer (Davis et al. 1994). 

Southern beaver may increase marking activity in the fall in response to 

increased food competition among colonies (Davis et al. 1994). Thus, 

scent marking in southern beaver may differ from that in northern 

beaver, which exhibit a peak of marking in the spring. 

Daily Activity Patterns. Beaver are crepuscular and nocturnal. In icefree areas, they follow a normal 24-hr period yearlong, but in northern 

latitudes, they do so only during spring, summer, and fall. Winter activity periods of northern beaver commonly exhibit a free-running circadian rhythm of about 26–29 hr, likely because relatively constant light 

conditions preclude entrainment of a photoperiod (Lancia et al. 1982). 

To survive extreme cold in winter, beaver remain under the ice or inside a lodge, where temperatures are nearer a relatively moderate 0◦ C. 

When beaver venture above the ice, ambient air temperatures below 

about −10◦ C cause substantial energy deficits. During extreme cold, 

beaver may exhibit no detectable movement inside the lodge (Aleksuik 

and Cowan 1969; Lancia et al. 1982), an energy-saving mechanism that 

may reduce caloric needs by 20% (McKab 1963). 

Dispersal and Other Movements. Bergerud and Miller (1977) classified the major movements of beaver as (1) movement of the entire 

colony between ponds within a territory; (2) short-term wandering of 

yearlings; (3) dispersal of beaver, usually at age 2 years, to establish new 

colonies; and (4) miscellaneous movement of adults, often following 

loss of a mate. Dispersal of 2-year-old beaver is the primary mechanism 

of population expansion. Dispersing individuals may return to the home 

colony for short periods of time, which suggests that dispersal is innate 

rather than learned from or encouraged by any aggressive behavior of 

parents (Hodgdon 1978). Dispersal of subadults often coincides with 

the birth of kits in the spring and/or high runoff, especially where ice 

in winter limits movements (Van Deelen and Pletscher 1996). Movements in ice-free areas are less restricted, as some dispersal occurs in 

late February and March, and scent marking and territorial defense may 

sal patterns are inconsistent (Gunson 1970; Van Deelen and Pletscher 

1996). Stochastic models of beaver population growth have assumed 

density-dependent dispersal rates (Molini et al. 1980). Distance of natural dispersal varies greatly, sometimes depending on the location of 

suitable but unoccupied habitat. Direction of dispersal can be either 

upstream or downstream within a watershed, or beaver can cross watersheds by overland travel of up to several kilometers. In a study of 46 

dispersing beaver in New York, 74% initiated dispersal downstream, 

35% moved to neighboring colonies, and females moved farther than 

males (Sun et al. 2000). In that study, 14% of dispersers were 1 year old, 

64% were 2 years old, and 21% were 3 years old. If the entire colony 

moves to a new location, then movement usually occurs before parturition; single animals usually disperse before pairs (Hodgdon 1978). 

Distances moved and time of movement are important considerations 

in formulating management strategies. 

Home Range. Home range of a beaver depends on sex, age, social 

organization of the family unit, type of occupied habitat, and seasonal 

constraints. During the summer, parental care for kits in and near the 

lodge or den can restrict the distance that adults can forage, with females 

staying closer to kits than do males. As young become more independent 

in the fall, the home range of adults may increase, although this is not 

always the case. In areas where ice confines movements in winter, home 

range is also constrained. For example, a radiotelemetry study of beaver 

in the taiga of southeastern Manitoba showed those in family units had 

smaller average summer home ranges (8 ha) than those in nonfamily 

units (18 ha) and that home ranges were larger in summer and fall than 

in winter (Wheatley 1997a, 1997b). 

Habitat features, especially shoreline configuration, strongly affect 

home range shape and size. Home ranges tend to follow the irregular 

shoreline patterns of lakes, ponds, rivers, and streams. Small ponds may 

contain only a single family unit with a relatively circular home range, 

but in lakes, streams, and rivers, the home ranges of beaver are typically 

larger and more linear (Novak 1987; Wheatley 1997c). However, these 

habitat-related patterns may break down when beaver are not living 

in a sedentary family unit or during seasonal movements (Wheatley 

1997c). In addition, intraspecific competition, or territoriality, is an important mechanism, which helps to regulate population density. Boyce 

(1981a) suggested that territoriality likely was responsible for a minimum intercolony distance of 1 km. Beyond that distance, availability of 

suitable sites for foraging, dams, and lodges more strongly influenced 

the distribution of colonies. 

Population Density. Beaver population density varies spatially and 

temporally. Because the home ranges of adjacent beaver families are 

usually separated by unoccupied habitat, density estimates typically include some unoccupied habitat. Factors that contribute to variation in 

density of beaver populations include human exploitation (trapping), 

water quality, habitat suitability, area available for new colonization, 

length of habitation time relative to available resources, epizootic diseases, local predation events, and territoriality. There is a wide range in 

the density of beaver colonies, from near zero to at least 4.6/km2 (reviews by Hill 1982; Novak 1987). Observers in different regions have 

attempted to estimate the maximum density or saturation point in local 

populations. Saturation has been reported to vary from 0.4 colony/km 

of stream in northern Alberta to 1.2 colonies/km of stream in New York 

and Utah (reviews by Hill 1982; Novak 1987). In the headwaters of four 

Alabama watersheds, saturation approached 1.9 colonies/km of stream 

(Hill 1976). 

Trapping can suppress beaver populations below habitat-based 

carrying capacity and is an important consideration in understanding 

population dynamics. Trapping often removes a larger percentage of 

adult beaver than it does other age classes; thus, it can increase adult 
and 53% in the second year (Zeckmeister and Payne 1998). Trapping 

can also alter the age structure of populations as removal of adults 

from established territories frees suitable habitat, allowing beaver to 

disperse earlier from their natal colony and increasing their survival 

(Boyce 1981b). Comparing harvested and unharvested beaver populations in New York, Muller-Schwarze and Schulte (1999) found that 

in unharvested populations, beaver colonized steeper stream gradients, 

young remained longer in the natal colony, preferred forage species 

were depleted and less preferred species were used more often, and 

beaver foraged further from their pond, lodge, or den. 

Density of beaver populations that occupy particular sites may also 

vary as a function of the length of time sites have been occupied. For example, after beaver returned to the Prescott Peninsula in Massachusetts 

following an absence of more than 200 years, the population showed 

slow growth the first 15 years, then 15 years of very rapid growth, and 

then a rapid decline in numbers until it stabilized at 23% of its peak. 

Populations in Sagehen Creek, California, also followed a pattern characterized first by slow growth, then rapid growth, then rapid decline to 

a level of relative stability (Busher and Lyons 1999). 

Observers monitoring short-term trends in beaver populations 

should consider these and other intrinsic population regulation mechanisms (such as territoriality) as factors that might explain population 

change. These intrinsic factors can be important confounding variables 

when attempting to understand extrinsic factors affecting beaver populations, such as trapping, anthropogenic habitat alteration, and competition with other species. 

Construction of Dams, Ponds, and Canals. Beaver are unique in 

their ability to create favorable aquatic habitat by building dams to 

restrict the flow of moving water, a behavior richly described in early 

literature on beaver and in many popular texts (Hilfiker 1991). The 

widely recognized beaver dam and beaver pond have made this seldom 

seen nocturnal rodent a familiar and well-studied mammal in North 

America. 

Dams may be initiated by pushing sediment, rocks, or sticks into 

a ridge formed perpendicular to the flow of moving water or by locating sites to take advantage of existing substrate (Hodgdon and Lancia 

1983). Structure is added by anchoring leafy branches, peeled branches, 

or other material to the substrate (stream bottom, stream banks, large 

rocks, or coarse, woody debris). Branches in the bulk of the dam may 

be anchored and intertwined perpendicular or parallel to the flow of 

water; however, material on the downstream side is usually placed with 

the cut end pushed into the stream bottom or bank and the branched 

end pointing upstream to support and stabilize the dam. 

Beaver use woody vegetation (bark may be peeled and eaten before placement in dams) and many other materials in dams. Dams can 

include conifers, sagebrush (Artemisia tridentata), tamarisk (Tamarix 

pentandra), aquatic plants, corncobs, cornstalks, plastic, metal, or 

other debris. Interestingly, when preferred foods are limited and lesspreferred foods are more abundant, beaver will select stems that are 

less palatable for dams and save the more palatable stems for food, 

especially for use in their winter food cache (Barnes and Mallik 1996; 

B. W. Baker, unpublished data). For example, Barnes and Mallik (1996) 

found that beaver preferred stems that were 1.5–3.5 cm in diameter and 

grew close to shore for dam-building material (mostly alder, Alnus 

spp.). They searched for and selected larger stems (>4.5 cm) that were 

further from the shore as food items. Thus, beaver increased risk of predation to obtain food but not dam-building material. Barnes and Mallik 

(1996) speculated that smaller stems were also better for construction 

of dams, as they might be easier to work with and provide a tighter 

seal against leaks. However, conventional wisdom suggests that larger 

material might make stronger dams in regions that experience high 

the dam laterally by adding shallow wings. Often several dams are built 

in succession, with water from each pond backed up to the base of the 

upstream dam, creating a stair-step pattern of dams and ponds, which 

flattens the slope of the drainage. 

The sound of running water is the primary cue for beaver to maintain and sometimes initiate dams (e.g., a noisy road culvert). Although 

beaver typically work on dams individually, sudden or loud sounds of 

running water may elicit cooperative behavior, especially to repair a 

breach in the dam (Aeschbacher and Pilleri 1983). Beaver of all ages 

inspect and repair dams, but adults perform most of the work. The literature is inconsistent about the relative efforts of males and females 

(Hodgdon 1978; Busher 1983). Beaver may initiate and maintain dams 

at any ice-free time of year; however, in many areas there is a peak of 

activity in the fall before freeze-up and again in the spring after high 

flows have subsided. 

The size and number of dams in a colony and the surface area 

and volume of water in ponds vary greatly depending on duration of 

occupancy, topography, substrate, flow levels, available vegetation, and 

other factors. As water spreads from primary dams within main channels, beaver often build small dams on the surface of the floodplain to 

further spread and direct water. Thus, individual dams and ponds can 

be very large or very small, with area inundated generally increasing 

through the first few years of beaver occupancy. 

Beaver often dig canals to facilitate movement of food and building 

material within and among their ponds or increase water depth for icefree access to a lodge or food cache. The longer that beaver occupy a 

site, the more likely it is that they will build or extend canals to access 

new foraging areas. Canals built within the pond may not be visible 

unless the pond is drained, but canals built in the floodplain may become 

obvious features of the landscape. Some canals may contain burrows 

with an underwater entrance to provide a refuge from predators. 

Beaver also create surface trails or “slides” as they transport woody 

material from their foraging area back to ponds and canals. These trails 

make it easier for beaver to drag material across the ground, permitting 

them to move material across greater distances. This is especially obvious in steep terrain, where gravity aids movement of material and can 

increase the effective foraging distance by several hundred meters. 

Lodges and Bank Dens. Beaver construct bank dens and lodges, which 

are used for protection from predators and weather. Bank dens are often 

dug under a large tree or shrub on the stream bank to provide support 

for the roof of the den. They have a nest area above the water level, an 

underwater entrance, and small holes in the surface soil to permit air 

exchange. Where beaver live exclusively in rivers or deep lakes, bank 

dens are typically the only housing structures that are built. Even where 

beaver eventually build dams and lodges, they often live in a bank den 

until more permanent structures are completed. The only place that 

bank burrows are completely absent is where the substrate prohibits 

their construction, such as areas with very rocky soils or permafrost. In 

many areas, lodges and bank dens are used. 

Lodges can be built in ponds or shallow lakes, where they are 

surrounded by water, or they can be built on the shore, often as an 

upward extension of a bank den. In this case, in which they often are 

called a bank lodge, beaver add sticks on top of the bank den and cut a 

hole to create a nest chamber. This process can be extended over several 

years if dam height and water level increase. Construction of a lodge in 

open water is similar, with sticks piled high enough to enable beaver to 

cut a nest chamber above the water surface. Mud is added to the surface 

of the lodge to provide a weather seal, but a portion of the top remains 

unsealed to allow air exchange. Beaver may have multiple active and 

inactive lodges within their territory. In addition to mud and freshly cut 

branches or dead sticks, beaver lodges may include some rocks or other 
Food Caches. In regions where ponds or streams freeze during the 

winter, beaver build food caches, which they access from their lodge 

by swimming under the ice. The use of food caches is uncommon or 

absent where beaver inhabit ice-free regions. Beaver typically build a 

cache by first floating cut branches in a deep part of the pond and then 

adding new material under this raft. The branches eventually become 

water-logged and sink to the bottom, holding the cache in place. The 

upper layer of the cache, called a cap or raft, becomes frozen in ice and 

unavailable to beaver. Interestingly, beaver often use inedible or lesspreferred species for the cap and place more-preferred food items deep 

enough in the cache to remain ice free and accessible throughout the 

winter (Slough 1978; B. W. Baker, unpublished data). Differential use 

of woody plants in food caches and dams can also occur. For example, 

beaver in Ontario preferentially used conifers and alder in dams and 

aspen (Populus tremuloides) and maple in food caches (Doucet et al. 

1994a). Quality of food items in caches is especially important in colder 

climates, where gestation, parturition, and feeding of newborn young 

occur under the ice. Construction of a winter food cache usually occurs 

in late fall and is often initiated by the first hard frost. Beaver may 

build multiple food caches in a single colony and often do not consume 

the entire cache during the winter. In the spring, barked stems from the 

cache may be used to maintain the dam. During ice-free months, beaver 

sometimes forage by cutting stems on land and returning to a favored 

location at the edge of a pond to consume them in safety, leaving a pile 

of peeled stems suggestive of a winter food cache. 

ECOLOGY 

Diet. Beaver are choosy generalist herbivores, consuming a diet of 

herbaceous and woody plants, which varies considerably by region and 

season. The number of plant species in the diet is highest in the southern 

part of the range and decreases toward the northern and alpine limits of 

the range (Novak 1987). Herbaceous plants make up much of the diet 

when they are available and succulent (actively growing). In the central 

and southern United States, beaver eat a variety of aquatic and riparian 

forbs and grasses as well as cultivated row crops and grains. Roberts 

and Arner (1984) found that beaver in Mississippi depended on the bark 

of woody plants in late fall and winter, but abruptly shifted their diet to 

herbaceous species after spring greenup in March. Using stomach analysis, they identified 16 genera of herbaceous plants, 15 species of trees 

and shrubs, and four woody vines in the yearlong diet. Woody material 

constituted 53% of the annual diet (86% in winter, 16% in summer); 

grasses occurred in 25% of stomach samples, including some collected 

in midwinter. In an Ohio study, herbaceous plants accounted for 90% 

of the feeding time during summer and 40–50% during spring and 

fall (Svendsen 1980b). In the Mackenzie Delta, Northwest Territories, 

leaves and the growing tips of willow (Salix spp.) were the main foods in 

July and August. Bark of willow (76%), poplar (Populus balsamifera) 

(14%), and alder (A. crispa) (10%) made up the diet the rest of the year 

(Aleksiuk 1970b). The protein:calorie ratio was 40 mg/cal in summer 

and 8 mg/cal for the rest of the year, indicating that beaver in northern 

areas shift their diet to high-protein willow leaves whenever they are 

available. In northern latitudes, water lily (Nymphaea, Nuphar) is often 

the most important herbaceous component of the diet (Novak 1987). Its 

edible rhizomes remain succulent after cutting and are often stored in a 

food cache for winter use (Jenkins 1981). A variety of grasses, sedges 

(Carex), rushes (Scirpus), and cattails (Typha) is important in the West 

and Southwest. 

Deciduous woody plants are usually the most important component of the diet of beaver and often are the primary limiting factor 

where ice forces subsistence on a winter food cache. Beaver eat the 

leaves, buds, twigs, noncorky bark, roots, and fruits of deciduous woody 

vak (1987) suggested that local populations of beaver in southern areas 

included more woody plant species in their diets than did northern populations, but at regional scales the number of woody species used was 

similar. 

Conifers also are cut or gnawed by beaver and used for food or 

building material, although their value varies greatly by region and 

availability of preferred deciduous species. In the eastern United States, 

loblolly pine (Pinus taeda) and Virginia pine (P. virginiana) may make 

up over half of the woody material cut by beaver (Novak 1987). They 

may repeatedly gnaw the bark of pine trees to obtain sap (Svendsen 

1980b) or sweetgum (Liquidambar styraciflua) trees to obtain storax, 

an aromatic balsam, which they lick from the injured site. In many areas, 

especially in their northern and western range, any substantial use of 

conifer is considered unusual and a sign that more-preferred species 

are lacking (Novak 1987). Dietary use of conifer also may be seasonal, 

as beaver in Massachusetts selected against pine during the fall, but not 

during the rest of the year (Jenkins 1979). 

Food Preference. Preference for a particular food item indicates “it 

constitutes a significantly larger fraction of the diet than an unbiased 

sample of items of the various food types available” (Jenkins 1981:560). 

Thus, some foods may constitute a large percentage of the diet, but may 

not be preferred over less available, but more favored species. 

Willow is often the most available and the most used woody riparian species in much of the beaver’s range. In many areas of the 

far north, Rocky Mountains, and intermountain west, beaver may depend entirely on willow to supply winter forage and building material 

(Aleksiuk 1970b). Where aspen or poplar is available, it is usually 

more preferred than willow (Jenkins 1981). Cafeteria-style feeding experiments in Ontario showed the following preferences (in descending 

order): aspen, white water lily (Nymphaea odorata), raspberry (Rubus 

idaeus), speckled alder (A. rugosa), and red maple (A. rubrum). Similar 

experiments in Nevada showed that beaver preferred aspen and avoided 

Jeffery pine (P. jeffreyi) (Basey 1999). 

Selection of forage items by beaver may be related to a variety of 

physical and chemical factors. Evidence suggests that beaver may select 

aspen resprouts based on their age-related growth form (Basey et al. 

1988, 1990). Aspen reproduces asexually by resprouting within a clone. 

Aspen clones that have been repeatedly cut by beaver produce juvenileform root sprouts (large leaves with an absence of lateral branching), 

which are avoided by beaver when compared to available adult-form 

root sprouts (small leaves with lateral branching). Although juvenileform aspen sprouts have more protein and likely provide better nutrition, 

they contain secondary metabolites that apparently cause avoidance 

by beaver. The importance of secondary metabolites to selection was 

further demonstrated in experiments where leaf extracts from different 

deciduous and coniferous species were painted on aspen leaves and then 

presented to beaver. Selection favored aspen leaves painted with extracts 

from deciduous species more so than those painted with extracts from 

coniferous species (Basey 1999). 

Retention time of forage passed through the digestive tract varies 

with diet composition (likely due to lignin and fiber content) and may 

also influence food selection by beaver. Experiments have shown that 

food preference and retention time are correlated; species with a shorter 

retention time, such as aspen, are more preferred than those with a 

longer retention time. Beaver “select a diet that maximizes long-term 

energy intake, subject to digestive limitations” (Doucet and Fryxell 

1993:201). Thus, retention time may influence intake rates and energy 

gained from different forage species, indicating it may be an important 

factor in food selection by beaver (Fryxell et al. 1994). 

Physical features of the food item may also influence selection. In 

an experimental study of foraging behavior, Doucet et al. (1994b) found 
trees available for food, red maple may be the only tree left standing 

at the edge of an older beaver pond. Odor may also affect selection. In 

a similar experiment using extracts of predator feces painted on aspen 

logs, there was a strong preference against the odors of coyote, lynx, 

and river otter. Thus, predator odors may be a useful management tool 

for preventing beaver damage (Engelhart and Muller-Schwarze 1995). 

Central-Place Foraging. Beaver typically cut woody vegetation from 

terrestrial locations for food or construction material and bring it back 

to a central place, such as a pond, cache, aquatic feeding station, lodge, 

burrow, or dam. Because this behavior creates exposure to predation 

and has high energetic costs, beaver have been used to test general predictions of central-place foraging theory. These predictions suggest that 

beaver should modify their behavior to concentrate foraging near the 

central place and should increase their selectivity for size and species 

away from the central place (Fryxell 1992). Most studies have confirmed these general predictions, but exceptions to these patterns occur. 

For example, studies confirmed that beaver typically cut increasingly 

smaller stems (less provisioning time) further from the central place, as 

predicted by optimal foraging models (Jenkins 1980; Belovsky 1984; 

Fryxell and Doucet 1990). In contrast, where relatively small (1.5– 

30 mm) stems are the only woody plants available, beaver may select 

larger stems even when located further from the central place (McGinley 

and Whitman 1985). Selection for larger stems is particularly evident 

where beaver occupy shrub habitats, such as those containing only 

smaller species of willow and alder. In some cases, repeated cutting by 

beaver can cause trees to develop and maintain a shrubby growth form 

(e.g., Fremont cottonwood, Populus fremontii; McGinley and Whitman 

1985). 

The size–distance relation in food selection by beaver also may 

be affected by species preferences. For example, Jenkins (1980) found 

that beaver cut larger stems of preferred species, such as oak and cherry 

(Prunus), further from the central place than less-preferred species. 

In contrast, although Belovsky (1984) did find that beaver had strong 

food preferences, preferences did not change relative to distance from 

beaver ponds. In many cases, the interaction of species preferences 

with stem size and distance from the central place has been difficult to 

document in the field because depth to water and other plant-growing 

conditions preclude equal availability of stems to beaver. Modeling the 

diet of beaver is one way to overcome limitations of field experiments. 

For example, Belovsky (1984:220) found that beaver at Isle Royale 

selected their diet “consistent with an energy-maximizing solution to 

a linear-programming model.” This energy maximization model was 

further confirmed by Fryxell (1992) with a second line of evidence, 

which found both density and distance were important predictors of 

food selection by beaver. 

Chemical factors and stem size may also influence stem selection 

by beaver. If aspen responds to repeated beaver cutting by producing 

a juvenile growth form, then higher concentrations of phenolic compounds (secondary metabolites) may inhibit further cutting by beaver 

and influence the predictive value of optimal foraging models for beaver. 

Basey et al. (1988) found beaver avoided aspen stems <4.5 cm in diameter in favor of those >19.5 cm in diameter near a 20-year-old beaver 

pond where 51% of stems had been previously cut by beaver and the 

remaining 49% of stems were in juvenile form. In contrast, beaver at 

a newly occupied site selected smaller aspen stems and against larger 

ones. Taken together, these results suggest that phenolic compounds, 

or other factors in addition to size of stem, may influence selection by 

beaver. 

Food Consumption and Production. Estimates of daily forage consumption rates (wet woody biomass) for beaver vary from 0.5 kg/day 

(Dyck and MacArthur 1993) to 2.0 kg/day (review by Stegeman 1954). 

could not be met from the submerged food cache in their study colony. 

Supporting research has shown that when food is limited, beaver may 

metabolize body tissue during winter. 

Estimates of beaver food (twigs and bark) produced by trees and 

shrubs may be useful for predicting the carrying capacity of beaver 

where woody biomass limits population density. Beaver food estimates 

are derived from graphs or equations that model annual production 

(current annual growth) and total biomass based on measures of basal 

stem diameter. Estimates have been derived for aspen (Aldous 1938; 

Stegeman 1954), willow (Baker and Cade 1995), and five species of riparian shrubs in Minnesota (Buech and Rugg 1995). The maximum 

diameter of twigs that are entirely consumed by beaver is a critical consideration in deriving estimates of beaver food. The diameter 

used is often based on assumptions made from observing the size of 

peeled stems, but may vary greatly by species and region. For example, 

Aldous (1938) assumed beaver ate all stem portions <12.7 mm in diameter for aspen, Buech and Rugg (1995) assumed <5 mm for Minnesota shrubs, and Baker and Cade (1995) assumed <3 mm for coyote 

willow (S. exigua). Application of results among studies and different woody species requires caution. In addition, intense ungulate or 

livestock herbivory of the terminal leaders on shrubs may strongly reduce the biomass of beaver food relative to unbrowsed stems of equal 

diameter (B. W. Baker, pers. obs.). 

Habitat Requirements. The ability of beaver to alter existing habitat conditions to meet their needs has allowed populations to inhabit a 

variety of natural and human-made habitats in North America. They 

have successfully colonized tundra and taiga in the far North, bottomland hardwood forests and marshes in the deep South, riparian areas 

in both cold and hot deserts, and elevations that vary from sea level to 

above 3400 m (reviews by Hill 1982; Novak 1987). Although beaver 

can occupy a wide variety of habitats, some generalizations are evident. A comprehensive evaluation of beaver habitat requirements in the 

Rocky Mountains showed they generally preferred wide valleys with 

a low (<6%) stream gradient, which offered relatively more food and 

reduced risk of severe floods (Retzer et al. 1956). Beaver typically inhabit streams with at least intermittent flow and lakes or ponds with 

standing water, but they can also inhabit bogs that lack open water. In 

Minnesota, they occur in sedge-moss and other bogs, where they can 

enlarge natural moats to create ponds of standing water and build floating lodges able to adjust to fluctuating water levels, and thus maintain 

protection from predators (Rebertus 1986). 

Early studies of beaver formed the foundation for later mathematical models, which quantified habitat requirements and created 

a framework for making and testing predictions. Slough and Sadleir 

(1977) sampled colony density and associated habitat conditions at 

136 lakes and 45 stream sites in Ontario and used regression analysis 

to develop a land classification system for beaver. Howard and Larson 

(1985) used principal component analysis of habitat variables to predict 

beaver colony density in Massachusetts. Percentage hardwood vegetation, watershed size, stream width, and stream gradient were important 

predictors in their classification system. Allen (1983) used existing literature and expert opinion to develop a general habitat suitability index 

(HSI) model for beaver, which used nine variables to rate habitat quality on a scale of 0.0–1.0. These variables included measures of canopy 

cover, height, stem diameter, species of trees and shrubs, stream gradient, water level fluctuation, and shoreline development (ratio of length 

and area). The HSI model assumed a minimum habitat area of 0.8 km of 

stream or 1.3 km2 of lake or marsh as a prerequisite of suitable beaver 

habitat. This model has been widely used by environmental planners 

to quantify potential impacts from development projects and mitigate 

habitat loss. 
tures of the stream, such as a lower gradient and a greater depth and 

width, were more important than vegetation in describing the location 

of lodge sites selected by beaver (Beier and Barrett 1987). In contrast, 

Barnes and Mallik (1997) found that concentration of woody plants 1.5– 

4.4 cm in diameter and size of the stream and its upstream watershed 

area were important predictors of dam-site location in northern Ontario. 

In Oregon streams, McComb et al. (1990) found that beaver selected 

dam sites where the substrate was less rocky, the water was shallower, 

the channel had a lower gradient, and woody vegetation (e.g., Alnus) 

had a greater canopy cover. They concluded that Allen’s (1983) HSI 

model was useful in predicting habitat quality for beaver at their sites, 

but required some site-specific modifications. 

In contrast, others have found that Allen’s HSI model was a poor 

predictor of beaver habitat quality in their region. For example, a Kansas 

study suggested that water quality, river substrate type, and adjacent 

agricultural land-use practices are important predictors of riverine habitat quality for beaver in the central United States (Robel et al. 1993). 

In an Oregon study, many potential beaver sites were highly rated by 

the HSI model even though they were unoccupied by beaver at the time 

of study, which suggested poor model performance to the investigators (Suzuki and McComb 1998). However, low density or absence of 

beaver in apparently suitable habitat is not unusual and may be caused 

by many non-habitat-based factors, such as trapping, disease, territoriality, or simply the inherent variation of natural systems. At occupied 

sites, cutting of preferred species by beaver may alter the density and 

species composition of vegetation, and thus affect how the habitat might 

be rated by habitat models (Suzuki and McComb 1998). 

MORTALITY 

Predation. Predation by the timber wolf (Canis lupus) can be an important limiting factor of beaver populations where they occur together. 

Wolves prey on beaver during the ice-free period, when nearly half their 

diet may consist of beaver (Potvin et al. 1992). In Algonquin Park, 

Ontario, as white-tailed deer (Odocoileus virginianus) populations declined over a 9-year period, beaver gradually became the most important 

prey item: 55% of wolf scats had beaver remains (Voigt et al. 1976). In 

an experimental study in Quebec, density of beaver colonies increased 

20% after 3 years of wolf control and then declined again after wolf 

control ceased, indicating wolf predation may have suppressed populations below the carrying capacity of the habitat (Potvin et al. 1992). 

Habitat conditions that force beaver to forage farther from water may increase predation rates by wolves. On Isle Royale, beaver foraged further 

(>100 m) from ponds when wolf populations were low and closer (<35 

m) to ponds when wolf populations were high (D. W. Smith, unpublished data). Thus, the impact of wolf predation on beaver populations 

can be locally significant, but varies greatly depending on wolf density, 

alternative prey availability, and other factors. 

Coyotes (Canis latrans) and mountain lions (Puma concolor) also 

prey on beaver, as do some other mammalian predators of generally 

minor importance, such as bears (Ursus spp.), wolverines (Gulo gulo), 

river otters (Lontra canadensis), lynx (Lynx canadensis), bobcat (Lynx 

rufus), and mink (Mustela vison) (review by Hill 1982). However, unusual circumstances can alter typical predation patterns. Black bear (U. 

americanus) predation strongly suppressed beaver populations on an island in Lake Superior (Smith et al. 1994). In this case, bears colonized 

one of two similar islands in the 1970s that beaver had colonized in the 

late 1940s or early 1950s. As the bear population grew, they focused 

predation on beaver, the only source of meat on the island, digging into 

18 of 26 beaver lodges and causing surviving beaver to concentrate 

foraging on trees <30 m from water. 

sponsible for the remaining human infections. It can be fatal to humans 

and has a terrestrial cycle in rabbits (Sylvilagus spp.) and ticks (Morner 

1992). Tularemia infections in beaver are typically subclinical without 

noticeable effects on the individual or the population, but they can be fatal to beaver and cause mass mortality from local or regional epizootics. 

Tularemia in beaver sometimes can be traced to infections in terrestrial 

rodents that deposit urine or feces in water, or die in water, which then 

harbors F. tularensis bacteria. For example, an outbreak of tularemia 

in Montana during 1939–1940 caused widespread mortality of beaver 

(several hundred carcasses were found) and coincident infection and 

mortality of meadow voles (Microtus pennsylvanicus) that inhabited 

the grassy streambanks (Jellison et al. 1942). Interestingly, rabies has 

been documented in beaver, but little is known about its pathogenesis or epizootiology (J. Rupprecht, 47th Wildlife Disease Association 

Conference, oral commun., 1998). 

Other Mortality. Starvation can be an important cause of mortality, 

especially at northern latitudes, when beaver are unable to construct a 

food cache large enough to sustain them through the winter (Gunson 

1970; Bergerud and Miller 1977). Sudden snowmelts in midwinter or 

violent spring breakups can raise water levels in streams and may destroy lodges and occupants or drown large numbers of beaver under the 

ice (Hakala 1952). 

BEAVER AS A KEYSTONE SPECIES AND 

AN ECOSYSTEM ENGINEER 

A keystone species is one that greatly influences the species composition and physical appearance of ecosystems (Paine 1969) and whose 

effects on ecosystem structure and function are both large overall and 

disproportionately large relative to its abundance (Power et al. 1996). 

An ecosystem engineer is a species that directly or indirectly controls 

resource availability by causing “physical state changes in biotic or 

abiotic materials” (Jones et al. 1997:1946). The beaver is a definitive 

example of both a keystone species and an ecosystem engineer. 

The dam-building, canal-building, and foraging activities of 

beaver have profound effects on ecosystem structure and function. 

Beaver dams slow current velocity, increase deposition and retention of 

sediment and organic matter in the pond, reduce turbidity downstream 

of the dam, increase the area of soil–water interface, elevate the water 

table, change the annual stream discharge rate by retaining precipitation runoff during high flows and slowly releasing it during low flows, 

alter stream gradients by creating a stair-step profile, and increase resistance to disturbance (reviews by Naiman et al. 1988; Gurnell 1998). 

Canals dug by beaver spread impounded water across a larger surface 

area, and thus magnify the effects of single dams. The foraging activity of beaver alters the species composition, density, growth form, 

and distribution of woody vegetation. These effects on vegetation and 

the physical characteristics of streams strongly alter the composition 

of the animal community. Because research did not begin until after 

beaver populations recovered following near extinction by presettlement trapping and extensive habitat loss, researchers have observed a 

human-impacted and likely conservative picture of how beaver have 

altered ecosystem structure and function (Naiman et al. 1988). 

Effects of Beaver on Geological Processes. In 1938, researchers evaluating the formation of broad, flat alluvial valleys in the Catskill region 

of New York discovered that geological processes alone could not explain observed sediment deposition rates (Ruedemann and Schoonmaker 1938). They suggested that during the 25,000 years since the 

last glaciation, layer on layer of sediment-filled beaver ponds caused 

the “complete aggrading of valley floors, originally in small descending 

steps, which disappear in time and leave a gently graded, even valley 
(Meentemeyer and Butler 1999). Thus, unless dams fail, beaver ponds 

will eventually fill with sediment and become beaver meadows. This 

process of accelerated meadow development by beaver dams is likely 

more important in meandering, low-gradient, valley-bottom streams, 

where conditions favor stable dams that spread sediment-laden water 

over a large surface area, rather than in steep, V-shaped, high-energy 

streams, where beaver dams tend to fail at a greater rate. 

Beaver dams also affect erosional processes within stream channels, typically increasing channel aggradation. As sediment-loaded 

water enters a beaver pond, it slows in velocity and drops sediment, 

increasing aggradation. However, water downstream of dams can be 

underloaded with sediment and increase erosional forces as the stream 

regains lost sediment (Meentemeyer and Butler 1999). This can lead 

to a localized increase in bank sloughing below beaver dams in areas 

with erosive soils. In most cases, the net effect of beaver dams is to 

decrease channel and streambank erosion and increase channel aggradation (Parker et al. 1985). Catastrophic beaver dam failures are rare 

events, but can occur following unusually large rainfalls or high spring 

runoffs. In 1994, a beaver dam in central Alberta failed and released 

7500 m3 of water, causing a flood wave that was 3.5 times the maximum recorded discharge for the stream (Hillman 1998). In this case, the 

flood wave was largely attenuated by downstream wetlands, including 

several beaver ponds. 

Beaver dams may also act as a filter to decrease nonpoint-source 

water pollution. In a study of Currant Creek, Wyoming, a highly erosive 

second-order stream, concentrations of suspended solids, total phosphorus, sodium hydroxide-extractable phosphorus (biologically available P), and total Kjeldahl nitrogen were reduced in water flowing 

through beaver ponds during high spring runoff (Maret et al. 1987). 

The effect of beaver ponds on these parameters continued during summer low flows, but was of lower magnitude. Effects disappeared at about 

1.6 km below the beaver dams, likely due to inputs from bank erosion 

(Parker et al. 1985; Maret et al. 1987). Beaver ponds may also influence 

water quality by affecting the number and composition of bacteria in 

the stream. In Wyoming, some species of bacteria apparently increased 

and others decreased as water flowed through beaver ponds; however, 

results were confounded by the effects of different livestock grazing 

systems (Skinner et al. 1984). 

Effects of Beaver on Ecological Processes. In addition to geological affects, beaver alter the landscape by creating layers of spatially 

distinct volumetric units, or patch bodies, which include the bedrock, 

the water-saturated anerobic soil under the pond, the moist aerobic soil 

at the water’s edge, the pond, the browse zone concentric to the pond 

or central place, and the overlying atmosphere (Johnston and Naiman 

1987). These patch bodies create a shifting mosaic of conditions in the 

landscape, which varies spatially and temporally as beaver populations 

colonize new territory or abandon old sites (Naiman et al. 1988). The 

inherent habitat matrix strongly influences how these patch bodies affect ecosystem process. Effects are greatest where contrast is greatest. 

Beaver that create dams in existing wetlands have less effect than those 

that dam streams in upland forest or desert shrubland. Basin geomorphology and length of occupancy also affect the magnitude of influence. 

Beaver typically select the best pond sites first and move to less desirable sites as populations grow or as resources are depleted. Ponds built 

in better sites have greater longevity and affect the disturbance dynamics in the system. In a Minnesota study, a series of aerial photographs 

between 1940 and 1986 showed the rate of patch formation was much 

greater during the first two decades following colonization than during 

the second two decades, which suggests that geomorphology eventually 

limited the availability of pond sites after the initial better sites were 

occupied (Johnston and Naiman 1990a). 

addition, the turnover time of carbon in beaver ponds averaged 161 

years, much slower than the 24 years found in riffles. Beaver ponds 

affect the amount and distribution of nitrogen in the system, as ponds 

create anerobic conditions, slow flows, and increase oxygen demand by 

retaining organic matter. In Quebec, a beaver-modified section of stream 

“accumulated 103 times more nitrogen than before alteration” (Naiman 

and Melillo 1984:150). Anerobic conditions caused by water-saturated 

soils in beaver ponds fundamentally alter biogeochemical pathways 

(Naiman et al. 1994). When beaver create ponds in forested uplands, 

most upland vegetation dies from inundation and woody material cut 

by beaver is moved to the stream for dams and lodges. The organic 

horizons of pond sediments accumulate chemical elements from formerly upland plants that become available for vegetative growth when 

the ponds fill with sediments or dams fail and abandoned sites become beaver meadows. Even small dams can accumulate a tremendous 

amount of sediment. For example, dams containing 4–18 m3 of wood 

retained 2000–6500 m3 of pond sediment in a boreal forest system in 

Quebec (Naiman et al. 1986). In a long-term Minnesota study, beaver 

activities increased the standing stock of chemical elements in the organic horizon of ponds by 20–295% (Naiman et al. 1994). Transport 

of water through beaver ponds can also neutralize acids, increase pH, 

and increase dissolved oxygen concentrations in acidic stream systems (M. E. Smith, et al. 1991). Thus, the activities of beaver can 

strongly modify the biogeochemical characteristics of stream systems 

and fundamentally influence forest ecosystem dynamics at landscape 

scales. 

Effects of Beaver on Invertebrates. Beaver ponds affect the species 

composition and abundance of stream invertebrates as the community responds to increased sediment deposition and still water behind 

dams. Invertebrate taxa that prefer running water are replaced by pond 

taxa. Community function is changed as collectors and predators increase in importance and shredders and scrapers decrease in importance 

(McDowell and Naiman 1986; Naiman et al. 1988). In Quebec, density 

and biomass of invertebrates in pond sites were two to five times greater 

than in riffle sites in the spring and summer, but were similar in the fall 

(McDowell and Naiman 1986). The number of species in ponds was 

similar to that in the natural stream channel, but resembled that in slowwater habitats of larger order streams, indicating that invertebrates in the 

beaver ponds may not be unique in the watershed (Naiman et al. 1988). 

In a study that compared stream riffle sites above and below beaver 

dams in the Adirondack Mountains, sites immediately below dams had 

lower invertebrate richness and diversity, but higher total invertebrate, 

predator, and collector–gatherer densities (M. E. Smith et al. 1991). 

Beaver may also affect the invertebrate community by changing 

the structure and chemistry of plant hosts. In a study of leaf beetles 

(Chrysomela confluens) and their cottonwood (P. fremontii × P. angustifolia) hosts, beetles were attracted to beaver-cut cottonwood regrowth 

even though it contained twice the level of defensive chemicals (to protect the plant from herbivory) as normal juvenile regrowth (Martinsen 

et al. 1998). In this case, beetles may have sequestered these chemicals 

for their own defense against mammalian predators. Beetles also may 

have obtained a nutritional benefit from beaver-cut regrowth because it 

contained more total nitrogen than nonresprout growth. Thus, beetles 

grew faster and were heavier at maturity. 

Beaver impoundments also may affect local mosquito populations, 

but not necessarily as conventional wisdom might suggest. At a New 

York site, observers noted marked reductions in mosquito populations 

after beaver impounded an area of poorly drained forest (Butts 1992). 

Before impoundment, the area supported large larval populations of 

the Aedes mosquito, which is unable to breed in the permanent water 

developed by beaver. 
pools, which resist freezing in winter (often capped with ice and snow, 

which prevents formation of anchor ice) and maintain cooler temperatures in summer. Beaver provide additional benefits by increasing the 

size of the wetland area, improving physical cover, and increasing the 

invertebrate forage base because of changes in the substrate and higher 

water temperatures in ponds (reviews by Hill 1982; Olson and Hubert 

1994). In Wyoming, standing stock (kg/ha) and density of brook trout 

(Salvelinus fontinalis) in beaver ponds were correlated with surface 

area, mean water depth, water volume, discharge into pond, elevation, 

and a morphoedaphic index (Winkle et al. 1990). However, where trout 

populations are limited by high water temperature in the eastern United 

States, beaver ponds may increase temperatures beyond tolerable limits, 

and beaver dams are often removed to improve trout habitat. However, a 

study of the thermal effects of beaver dams in Wisconsin found no consistent relationship between size or number of beaver ponds and degree 

of downstream warming (McRae and Edwards 1994). They found that 

large ponds may act as thermal buffers, which dampen daily fluctuations 

in water temperature and only slightly raise downstream temperatures. 

Thus, large-scale beaver dam removal in headwater streams may have 

net negative consequences on trout populations as their positive effects 

on invertebrates and ecosystem processes are lost. 

Beaver dams may be detrimental to populations of trout and salmon 

if they restrict or prevent fish passage. However, some studies have 

shown that trout can pass over dams during high water and may pass 

through newly constructed dams at any season (review by Olson and 

Hubert 1994). In the Pacific Northwest, many beaver dams are partially washed out each year by winter high water. However, dams can 

still benefit fish that use the remaining ends for cover, thus providing 

value as coarse, woody debris. During summer low flows in this area, 

beaver dams improved rearing habitat for coho salmon (Oncorhynchus 

kisutch), as beaver ponds were larger and contained more coho fry than 

pools without beaver (Leidholt-Bruner et al. 1992). 

Beaver activities can have profound effects on fish community 

structure. In an experimental study of a headwater stream in northern Minnesota, beaver ponds appeared to act as reproductive “source” 

populations for fish, which dispersed to adjacent streams, which functioned as reproductive “sinks” in the landscape. Thus, the boundary 

influences of beaver ponds were “critical in controlling fish dispersal 

between ponds and streams and the subsequent abundance and composition of fish in lotic ecosystems” (I. J. Schlosser 1995:908). The age 

and size of beaver ponds also affect stream dynamics. In Georgia, fish 

species richness per pond increased until ponds were 9–17 years old 

and then decreased as ponds aged in headwater streams, but showed little change relative to pond age in downstream sections (Snodgrass and 

Meffe 1998). In larger ponds, fish species shifted from lotic to lentic 

species, and larger predators replaced small-bodied minnows in older 

ponds. The size of beaver ponds is also important. As expected from 

general species–area relationships, fish species richness increases with 

size of pond, but very small beaver ponds can have higher than expected 

richness compared to ponds of a similar size not impounded by beaver 

(Keast and Fox 1990). Thus, beaver have a strong effect on fish species 

richness, but the effect is dependent on the size and age of beaver ponds 

and how ponds are distributed within the landscape. 

Effects of Beaver on Vegetation. Beaver affect vegetation by building 

dams and removing woody plants as food and building material. Beaver 

dams raise the water table by creating a pond area that may be inundated 

by several meters of water and an umbrella-shaped zone of influence 

that radiates out from the pond, creating a new water table gradient 

controlled by soil texture and other factors. The soil behind dams can 

act like a sponge, retaining water during wetter months and slowly releasing it during drier months. In areas of low or irregular precipitation, 

willow as dams alter hydrological and ecological conditions within incised stream channels (B. W. Baker, pers. obs.). Higher water tables 

caused by beaver ponds generally kill upland vegetation and promote 

establishment and growth of wetland vegetation. 

Beaver can improve conditions for seedling establishment of willow, cottonwood, and other riparian species. Sediment deposited behind 

beaver dams creates an ideal moist soil substrate, which can become 

exposed as water levels in the pond decrease due to a dam washout or 

other cause. Beaver cuttings may be an important mechanism of plant 

establishment for some woody species such as willow (Cottrell 1995). 

Stems that are cut by beaver but not eaten can become imbedded in 

dams, lodges, or moist soil in or near ponds and sprout adventitious 

roots and new stem growth. Because a high percentage of stem segments is not consumed by beaver, they may substantially contribute to 

plant establishment, although the relative importance of this method is 

not well understood at the community level. 

Cutting by beaver can stimulate vigorous resprouting, which may 

increase biomass production in many woody riparian species. Plants 

can sprout new shoots by activating dormant meristems located below 

the cut on the same stem or on below ground plant tissue, or from previously developed root suckers. In a study of red willow (S. lasiandra) 

in Oregon, trees that had a higher percentage of stems cut by beaver 

responded by producing a higher percentage of regrowth the following season (Kindschy 1985). Where stem cutting is concentrated in 

late fall to build dams or prepare a food cache, plants are dormant 

when cut and respond with new shoots in the next spring in an attempt 

to recover former root:shoot ratios, maximizing plant production and 

minimizing plant damage. Cutting by beaver can also stimulate plants to 

initiate growth earlier in the spring, further increasing stem production 

(Kindschy 1989). However, biomass of new shoots can be decreased if 

regrowth is browsed by native ungulates or livestock. 

The interaction of stem cutting by beaver and intense browsing by 

livestock or native ungulates can strongly suppress regrowth and may 

result in declining riparian plant communities. Summer browsing by 

livestock that congregate along riparian areas can be particularly detrimental to recovery of beaver-cut willow, when new green shoots become 

highly preferred as grasses cure and become less palatable (Kindschy 

1989). Intense browsing by native herbivores can also severely suppress 

regrowth of beaver-cut stems. When beaver cut tall stems, regrowth occurs at or near ground level, placing the apical portions of stems within 

easy reach of herbivores. Browsing the tips of stems (leaders) releases 

apical dominance and may cause plants to develop a short stature. In 

an experimental study at Rocky Mountain National Park, Colorado, intense elk (Cervus elaphus) browsing of willow (S. monticola) regrowth 

during 3 years following simulated beaver cutting produced plants of 

low vigor, which were small, short, and hedged with a high percentage 

of dead stems (B. W. Baker, unpublished data). In contrast, regrowth of 

unbrowsed plants was vigorous, large, tall, highly branched, and leafy 

with a low percentage of dead stems. Browsed and unbrowsed plants recovered more stems per plant (about 70 after 3 years) than were present 

before simulated beaver cutting, but elk browsing strongly suppressed 

recovery of plant biomass. After 2 years of regrowth, browsed plants 

had recovered only 6% of their precut biomass, whereas unbrowsed 

plants had recovered 84%. Thus, beaver cutting and elk browsing may 

interact to decrease woody plant height and biomass, eventually reducing beaver habitat suitability and the positive effects of beaver on 

community structure and function. 

Foraging by beaver can significantly alter forest composition and 

plant succession. Besides humans, beaver are the only species in 

North America that can affect overstory vegetation by felling mature 

trees (Johnston and Naiman 1990b). In contrast to many other herbivores, beaver foraging is restricted to a central place within riparian 
and Naiman 1990b). Selective foraging decreased aspen and increased 

alder and conifer, with long-term effects on forest succession. In Wisconsin, beaver substantially reduced the density of preferred understory 

tree species (W. J. Barnes and Dibble 1988). Because understory species 

normally replace overstory species in areas without beaver, it was predicted that selective foraging by beaver strongly altered riparian forest 

succession. Donkor and Fryxell (1999) also found that the foraging activity of beaver altered forest succession by replacing deciduous species 

with conifers. They suggested this detracted from the keystone role of 

the beaver because the already dominant conifer community was increased. 

Woody plant communities along major river systems can also be 

affected by the foraging behavior of beaver. In rivers too large for beaver 

to dam, bank-dwelling beaver can have significant effects on the structure of woody riparian vegetation. Regulation of rivers by major dams 

can modify the effects of beaver as peak flows are decreased and base 

flows are increased, which affects growth of woody vegetation and its 

use by beaver. In a comparative study of the unregulated Yampa River 

and the regulated Green River in northwestern Colorado, Breck (2001) 

found that beaver harvested a higher percentage of willow and cottonwood on the regulated river, where the constant flow regime caused 

vegetation patches to be more uniformly available to beaver. In the unregulated river, shifting channels constantly changed access to shoreline 

vegetation. 

Abandonment of beaver ponds creates new habitat for plant establishment. Beaver meadows dominated by grasses and sedges often 

develop on the rich sediment that settles in beaver ponds. Meadows 

may eventually be replaced by forests, but in some cases succession is 

slower than expected. In northern forests, beaver meadows may resist 

invasion by conifers and persist for many decades as graminoid meadows (Terwilliger and Pastor 1999). Successful conifer (Abies, Picea) 

invasion requires the presence of ectomycorrhizal fungi, which form 

an obligate association with tree roots. Because past flooding would 

have killed these necessary fungi, beaver meadows require dispersal of 

fungi from nearby forest soils before conifers can invade. One possible 

mechanism of ectomycorrhizal fungi dispersal is via small-mammal 

feces. However, an evaluation of the red-backed vole (Clethrionomys 

gapperi) as a vector showed only about one third of plants grown in 

beaver meadow soils inoculated with vole feces had ectomycorrhizae 

present, compared to 100% of plants grown in forest soil. In addition, 

the potential of red-backed voles to facilitate dispersal of fungi is limited 

by their general avoidance of beaver meadows (Terwilliger and Pastor 

1999). Thus, persistence of beaver meadows in forest communities may 

be controlled by complex ecological mechanisms. 

Effects of Beaver on Mammals. A variety of mammals use the lush 

vegetation around beaver ponds as food and cover or rely on beaver 

to provide aquatic habitat (review by Olson and Hubert 1994). Beaver 

ponds are often important habitat for moose (Alces alces) because they 

increase production of woody plants and aquatic vegetation, which can 

contribute substantially to their total diet. In some cases, moose may 

compete with beaver for limited food supplies; however, the extent of 

their interaction and its effect on riparian vegetation are not well understood. Elk and deer can also be attracted to the increased abundance, 

palatability, or availability of woody and herbaceous forage at beaver 

ponds. Beaver ponds also create habitat for other semiaquatic mammals, 

such as river otter, mink, and muskrat, some of which may occur in a 

large percentage of active or abandoned ponds. In Idaho, the density and 

standing crop biomass of small-mammal populations was two to three 

times higher in willow-dominated beaver pond habitat than in adjacent 

riparian habitat (Medin and Clary 1991). Montane voles (M. montanus) 

and shrews (Sorex spp.) were the most abundant small mammals in the 

gpgg

ever, few studies have quantified these effects and some conclusions 

have been equivocal. For example, Russell et al. (1999) compared new 

(<5 years) and old (>10 years) beaver ponds to unimpounded streams 

in South Carolina. They found that richness and abundance did not differ among sites for amphibians, but both were higher for reptiles at the 

older beaver ponds than at new ponds or unimpounded streams. Reptile 

species diversity was highest at old ponds, intermediate at new ponds, 

and lowest at unimpounded sites. They suggested that beaver have generally benefited herpetofauna in the Piedmont of South Carolina, as the 

range of several species, such as common musk turtle (Sternotherus 

odoratus) and eastern mud turtle (Kinosternon subrubrum), has increased concurrent with the range expansion of beaver. 

Effects of Beaver on Birds. Waterfowl use beaver ponds for nesting 

and brood-rearing habitat and as stopover sites during migration. Beaver 

ponds enhance vegetation growth, which improves dense nesting cover 

and enhances interspersion of cover and water, improving nest isolation for territorial waterfowl pairs and increasing nest density (review 

by McCall et al. 1996). When beaver ponds flood timber, dead trees provide nesting sites for waterfowl (cavity nesters) that are relatively safe 

from predators. Beaver ponds increase the production of invertebrates 

and aquatic vegetation, which improves brood-rearing habitat. The benefits of beaver ponds to waterfowl may be expressed by increased 

production of waterfowl as regional beaver populations increase. For 

example, when beaver populations in south-central Maine increased in 

the 3–4 years following a trapping closure, density of Canada geese 

(Branta canadensis), hooded mergansers (Lophodytes cucullatus), and 

mallards (Anas platyrhynchos) also increased, as did the number of 

wetlands used by these species (McCall et al. 1996). Waterfowl in Finland also responded positively to increasing beaver populations, but 

response varied by species. Teal (Anas crecca, the European race of the 

green-winged teal) increased to become the dominant species during 

the first 2 years following flooding by beaver, but populations of mallards and wigeon (Anas penelope) did not respond (Nummi and Poysa 

1997). 

Beaver ponds can be preferred to similar open-water wetlands by 

breeding waterfowl. In Ontario, open-water lakes made up 47% of the 

study area, but were avoided by blue-winged teal (Anas discors), mallards, and wood duck (Aix sponsa). However, beaver ponds constituted 

only 25% of the area and were preferred by wood ducks (Merendino 

et al. 1995). Preference for beaver ponds may be due to their increased 

production of invertebrates important to waterfowl broods. For example, populations of water fleas (Cladocera spp.), a small invertebrate 

preferred by young ducklings, were abundant in first-year beaver ponds, 

with populations of larger invertebrates more important in 2- and 3-yearold ponds (Nummi 1992). Beaver ponds substantially enhance waterfowl habitat in the western United States, where riparian areas constitute 

<2% of the landscape. Breeding waterfowl surveys in Wyoming found 

that streams with beaver ponds had 7.5 ducks/km, but similar streams 

without beaver ponds had only 0.1 duck/km (McKinstry et al. 2001). A 

survey of 125 land managers found that beaver had been removed from 

23% of 28,297 km of Wyoming streams and that >3500 km of streams 

without beaver had potential for beaver reintroduction to improve waterfowl nesting habitat (McKinstry et al. 2001). Finally, beaver ponds can 

be highly important for migrating waterfowl throughout North America 

and for wintering waterfowl in ice-free southern regions (Ringelman 

1991). 

In addition to waterfowl, a variety of other bird species benefit 

from beaver activity. Beaver ponds can increase the area of open water, length of the shoreline, density of dead standing trees, and biomass, 

height, and canopy cover of shrubs. The abundance and diversity of terrestrial insects important to foraging birds are enhanced by changes in 
phoeniceus), Brewer’s blackbirds (Euphagus cyanocephalus), common 

snipe (Gallinago gallinago), and spotted sandpipers (Actitis hypoleucos) in Wyoming (Brown et al. 1996). In South Carolina, beaver ponds 

were an important avian habitat in all seasons, but reached maximum 

bird diversity in spring and summer and maximum number of individuals (all bird species combined) during fall migration (Reese and 

Hair 1976). Beaver ponds are especially important in arid environments, 

where riparian–wetland habitat provides an oasis for birds. Any increase 

in area or structural complexity of riparian vegetation usually benefits 

the avian community. 

ECONOMIC STATUS, MANAGEMENT, 

AND CONSERVATION 

Economic Value. The ecological role of beaver discussed in the previous section has tremendous indirect economic benefit through wetland 

creation, water storage, improved water quality, erosion control, sediment deposition, and recreation. These indirect benefits may far outweigh the direct monetary value obtained from their fur, and may offset 

any direct or indirect costs due to beaver damage. However, because 

the monetary value of these indirect ecological benefits has not been 

quantified, fur trapping and damage control are typically considered of 

primary economic importance. 

Native Americans valued beaver for food and clothing and early 

Europeans valued the underfur of beaver pelts for the manufacture of felt 

hats. In 1610, France granted Samuel de Champlain the first fur-trading 

monopoly in North America, initiating 200 years of intensive beaver 

trapping, which continued until the early 1900s, when beaver populations had been nearly extirpated and demand for felt hats had declined 

(reviews by Hill 1982; Hill and Novakowski 1984; Novak 1987). Since 

then, strict harvest regulations, reintroduction programs, and cutting 

and burning of climax boreal forests (setting back succession) have 

greatly benefited beaver populations. Annual harvests during the 1980s 

sometimes exceeded 1 million beaver pelts, more than recorded at any 

other time (Novak 1987). Although beaver trapping is still an important part of the fur industry in Canada and the United States, erratic 

and relatively low pelt prices have caused the economic importance of 

trapping beaver (numbers marketed and value of pelts) to decline relative to furbearers such as red fox (Vulpes vulpes), mink, and several 

other species (Hill and Novakowski 1984; Novak 1987). In addition, the 

value of beaver pelts varies by region, with those from warmer southern climates valued lower and those of colder northern climates valued 

higher. Pelt prices are a primary incentive for most trappers. Prices influence annual harvest levels and the ability of resource managers to use 

recreational trapping as a tool to reduce beaver populations or remove 

unwanted individuals. 

Strict trapping regulations or trapping bans can limit beaver trapping as a management tool. In recent years, recreational trapping has 

been the target of animal rights groups, which have successfully used the 

public initiative/ballot referendum process in some states (e.g., Amendment 14 in Colorado, November 1996) to eliminate or severely curtail 

trapping of furbearers. The long-term implications of trapping bans on 

beaver populations in these areas remain to be determined. One possible outcome may be that in some areas where private landowners once 

considered beaver a valuable fur resource they may instead be viewed 

as a pest species, with negative consequences to populations (Hill 

1982). Regulations that control or ban recreational trapping in many 

jurisdictions do not apply to landowners who are protecting private 

property. 

Beaver Damage. Expanding populations of humans and beaver inevitably lead to property damage. From the point of view of a landowner 

by plugging culverts) and pastures, eating or flooding agricultural crops 

(e.g., corn), damage to timber by flooding and cutting (mainly in the 

relatively flat Southeast), burrowing damage to dikes, ditches, and dams 

(mainly the arid West), cutting or flooding ornamental plants around 

homes or businesses, flooding habitat of rare plants or animals, damaging wild trout habitat, damaging fish ponds by plugging the overflow pipe, and potentially increasing the risk of human infection via 

Giardia lamblia, although some data suggest this is unlikely (Hill 1982; 

Woodward et al. 1985; Hammerson 1994; Olson and Hubert 1994). Annual cost of damage can be very high. In the early 1980s, annual beaver 

damage in the United States was estimated at $75–100 million; in the 

Southeast, the 40-year cumulative damage was estimated at $4 billion 

(review by Novak 1987). 

The importance of timber damage in the southeastern states was 

recognized soon after beaver were reintroduced; timber damage there 

far exceeds all other types of complaints (review by Hill 1982). Timber 

damage was reported by 67% of respondents to landowner questionnaires in Alabama (Hill 1976). In South Carolina, a 1984 survey showed 

beaver flooded >35,000 ha of timber, often flooding trees during the 

entire growing season with low dams <0.5 m high (Woodward et al. 

1985). If the root systems remain inundated for one to two growing 

seasons, many species of tree usually will die. Beaver kill timber of all 

size classes, with loss of larger trees causing greater financial impact 

on producers. Beaver frequently gnaw bark from hardwoods, which 

increases the risk of disease and subsequent rotting. 

Damage Control. Killing unwanted individual beavers and controlled 

harvests of beaver populations are the most common, and often the 

most effective, methods of reducing beaver damage, even though lethal 

control is becoming increasingly less acceptable to the public. In Mississippi, about 20,000 beaver are harvested annually, with 80% of the 

carcasses discarded without use of meat or fur (Schulte and MullerSchwarze 1999). Nonetheless, annual harvest may be the most prudent 

approach to animal damage problems, particularly where such harvest 

can involve citizen participants with no resultant public expense (Hill 

1974, 1976). Trapping techniques for taking beaver vary with trapper 

preference and climatic conditions, the greatest differences occurring 

between areas that have extremely thick ice and those that are ice free. 

Successful harvest techniques involve shooting, snaring, and trapping 

with either No. 3 or No. 4 leghold traps or No. 330 Conibear traps (Hill 

1982; Miller and Yarrow 1994). Shooting beaver from boats or from 

land may or may not be an effective control method (Hill 1982; Olson 

and Hubert 1994) and raises significant safety concerns. Alligators (Alligator mississippiensis) have been evaluated as a control method in 

the Southeast, but are generally not effective (Hill 1982). Poison bait 

substances, such as strychnine alkaloid baits and compound 1080, have 

been evaluated as a lethal control method, but are not approved for this 

purpose. They also pose political and practical problems, which will 

likely preclude their development (Hill 1982; Hammerson 1994). Thus, 

if the decision is to kill problem beaver, then trapping likely remains 

the most effective method. 

However, trapping beaver can be an ineffective control measure if 

landowners create a sink population by trapping beaver from their own 

land but fail to reach consensus for control among adjacent landowners containing a source population of beaver. Even when consensus 

for control is reached, migration of beaver from less-controlled sites to 

more-controlled sites imposes an external cost (negative diffusion externality) when landowners must incur the future cost of repeated trapping (Bhat et al. 1993). When attempting to minimize beaver damage to 

timber resources, the cost of trapping must be weighed against the benefit of increased timber production. Integrating a trapping plan with a 

timber plan via a cost-minimizing, area-wide bioeconomic model may 
migrants from June to September, or until dispersal rates are relatively 

low (Houston et al. 1995). In some cases, trees may tolerate relatively 

high levels of beaver damage without any major effect on the forest. In 

a study of beaver damage to bald cypress (Taxodium distichum) trees 

in Texas, 85% of the trees near lodges had their bark peeled by beaver 

with only minimal effects on tree survival (King et al. 1998). Thus, 

managing timber damage requires understanding the response of the 

particular tree species to foraging and flooding by beaver, gaining cooperation of all landowners within the affected area, and evaluating 

costs and benefits of beaver control relative to timber production. 

Livetrapping and relocation of problem beaver is more acceptable 

to the general public and has become fairly popular in urban areas. 

However, this can be cost prohibitive without volunteer labor and is 

not an option if suitable relocation sites are not available (Hammerson 

1994). Moreover, released beaver may suffer high mortality from predation or from their inability to successfully assimilate into established 

populations. Hancock traps are usually preferred to Bailey traps for 

removing problem beaver, although properly used snares may be more 

effective and less costly than either trap type (Hill 1982; Novak 1987; 

Hammerson 1994; McKinstry and Anderson 1998). In some situations, 

hand-held nets can help capture beaver on land or in shallow water from 

boats (Rosell and Hovde 2001). Chemosterilents and surgical sterilization also have been evaluated for beaver control, but remain impractical 

for treating wild populations (reviews by Hill 1982; Hammerson 1994). 

Beaver repellents or wire fencing may be an effective means of 

protecting plants from cutting or discouraging beaver occupancy of selected sites. Tree trunks can be protected by hardware cloth, chain link, 

or similar wire mesh connected at the ends (leaving room to allow tree 

growth) and extending about 1 m above the ground (Hammerson 1994). 

A solution of 10% creosote and 90% diesel fuel sprayed or painted on 

tree trunks reduces gnawing damage by beaver, as does a mixture of 

acrylic paint and sand, which acts as an unpalatable abrasive. Commercial deer repellents (Thiram, Magic Circle) may also be effective 

chemical repellents (Hammerson 1994). Chemical extracts from native 

tree species that beaver avoid (Jeffery pine) also may be effective as a 

beaver repellent (Basey 1999). Marking areas with beaver scent (artificial scent mounds) may discourage occupancy in the short term, but this 

method is likely an ineffective long-term solution. Scent marking by 

beaver more likely acts as a form of territoriality rather than as a scent 

fence (Welsh and Muller-Schwarze 1989; Sun and Muller-Schwarze 

1998; Schulte and Muller-Schwarze 1999). 

Flooding by beaver can often be prevented or managed by installation of beaver-proof road culverts and other water control structures 

or by installation of flow control devices in existing beaver dams (Fig. 

15.3). Damage occurs when beavers plug culverts or impound water 

against the beds of roads or railroads, causing flooding or washouts. 

Techniques for minimizing or preventing beaver from plugging road 

culverts include using oversized pipe-arch culverts (Fig. 15.3A), lowprofile box culverts (Fig. 15.3B), and various designs of beaver exclosure fencing (Fig. 15.3C) which prevent beaver from building a dam 

at the upstream end of a road culvert (Buech 1985; Hammerson 1994; 

Olson and Hubert 1994; Jensen et al. 1999; S. Lisle, oral communication, Beaver and Common-Sense Conflict Solutions Conference, 1999). 

In most cases, preventing damage with proper culvert design is far more 

cost-effective than the repeated, labor-intensive unplugging of dammed 

culverts or removing unwanted beaver (Jensen et al. 1999). Flow control devices installed in existing beaver dams have been very effective 

at mitigating damage to roads or other developments while maintaining 

the ecological and esthetic values of beaver presence. For example, the 

Clemson beaver pond leveler (Fig. 15.3D) can control the water level in 

beaver ponds by using tubes or similar structures laid perpendicular to 

the dam with the upstream end porous and protected from plugging by 

habitat changes that are unacceptable to landowners. 

Methods for controlling beaver or their damage often require special training, materials, and permits. State and local regulations should 

be consulted before attempting to control populations or to mitigate 

damage, such as by installing water control structures that affect instream flow. 

Public Opinion. Public opinion is an important consideration when 

choosing methods to control beaver damage. Many people have an 

emotional attachment to beaver and are vehemently opposed to any 

control methods that may cause their pain, suffering, or death. However, 

attitudes toward beaver control methods vary greatly among individuals, communities, regions, and type of land tenure. Rural residents, 

especially in agricultural areas, may have less opposition to lethal control than urban residents. People who experience beaver problems may 

accept harsher control than those without problems. Cultural values 

attributed to the presence of beaver also vary by region. Beaver may 

be more socially and economically valued in regions of Canada and 

the northern United States than in the Southeast, where fur values are 

lower, damage to timber and development is more severe, and beaver 

have less historical and cultural value. 

Social acceptability of beaver control depends on many factors. 

Residents in suburban areas of New York were willing to accept increasingly invasive control when they had increasingly severe concerns about 

problems (Loker et al. 1999). Contrary to predictions, residents were 

willing to use more severe control measures for nuisance and economic 

damage problems than for concerns about public health and safety (results combined for white-tailed deer, Canada geese, and beaver). In 

another New York survey, nearly 50% of stakeholders took lethal actions to solve beaver problems; highway superintendents were more 

likely than the general public to attempt to solve beaver problems and 

to use actions that were nonlethal but invasive (Enck et al. 1997). In 

Wyoming, managers of private and public lands were concerned that 

beaver caused problems when they blocked irrigation ditches, girdled 

timber, blocked culverts, and flooded pastures, roads, crops, and timber. 

However, 45% of private landowners with beaver on their land and all 

public land managers were interested in the proactive use of beaver for 

riparian management (McKinstry and Anderson 1999). 

Population and Harvest Management. Do beaver populations “need” 

to be harvested so they do not “eat themselves out of house and home ?” 

This management philosophy is pervasive in the culture of laypeople 

and professional wildlife managers. But is it true ? Why would beaver 

need the help of humans to control their populations, whereas nongame 

mammals seem to manage just fine without it (aside from pervasive 

anthropogenic stressors) ? How does the absence of wolves or other 

predators affect beaver carrying capacity ? Clearly, answers to these 

questions are beyond the scope of this chapter, but recent evidence 

provides some interesting discussion points. For example, densities of 

beaver colonies did not differ in a comparison of unexploited, saturated 

populations and exploited, thinned-out populations. Beaver in the saturated populations, however, colonized steeper gradients, had families 

with a larger percentage of 3-year-olds, depleted preferred trees and 

fed on less palatable species, and extended trails to more distant foraging sites (Muller-Schwarze and Schulte 1999). Because the maximum 

density of colonies (usually a minimum distance of about 0.9 km between colonies) may be controlled by territorial behavior rather than 

by habitat conditions, beaver populations in optimum habitat may become saturated or self-limiting below habitat-based carrying capacity. 

Beaver typically maintain intercolony distances and body weight regardless of population density. In some areas, forage near the central 

place may become temporarily depleted or ponds may become silted-in, 

causing colonies to periodically move to former beaver habitat that has 
Oversized pipe-arch culvert Low-profile box culvert 

C D 

Beaver exclosure fencing Clemson beaver pond leveler 

F 15.3. Examples of water control structures used to manage beaver (Castor canadensis) impacts. S: Adapted in part from Jensen et al. (1999). 

recovered or to new habitat. In other areas, beaver may persist indefinitely within the same stream reach. In the Rocky Mountains, beaver 

may temporarily abandon mixed aspen–conifer sites after removing 

available aspen from nearby uplands, but may indefinitely occupy 

riparian–willow sites, where dams create moist, bare soil and a high 

water table, which helps establish and perpetuate the willow community. Despite lack of any inherent control needs, beaver harvest provides valuable recreational and income opportunities for trappers and 

is the primary means of reducing beaver damage to timber and other 

resources. Thus, justification for beaver harvest should be based on 

the economic value of fur trapping or “managerial decisions [that] address conflicts between beaver and humans, and not necessarily any 

requirements of the beaver themselves” (Muller-Schwarze and Schulte 

1999:176). 

Beaver populations are managed by state, provincial, and territorial wildlife agencies in the United States and Canada. Agencies are 

responsible for setting seasons, setting bag limits or area-specific quotas, licensing trappers, stamping or tagging pelts, licensing fur dealers 

and auction houses, and enforcing laws and regulations (Novak 1987). 

Trapper education is an important part of beaver management. Trappers in the field influence the age, sex, and distribution of animals 

removed as they make decisions about how, when, and where to set and 

check traps. Harvest rates, or quotas, are based on allowable harvest 

to maintain sustained yield. Rates suggested by different studies have 

varied from 10% to 70%, depending on habitat type, elevation, and 

region. The most typical recommended annual harvest rate is 20–30% 

of the population, which is about 1.0–1.5 beaver/colony/year. Beaver 

are highly vulnerable to overharvest, so managers must closely monitor populations. Their slow rate of reproduction and delayed sexual 

maturity preclude reproduction as a means to offset intensive annual 

harvest. 

Regional differences among habitat types and land management 

prescriptions warrant regional beaver management plans (Snodgrass 

1997). Managing beaver by managing their food supply may be possible 

in some regions. For example, prescribed burning may encourage aspen 

production in mixed conifer habitat, but may be of limited value where 

multiple forage species are available. 

Using Beaver for Habitat Restoration and Improvement. The ability of beaver to store water, trap sediment, reduce channel erosion, 

and enhance establishment and production of riparian vegetation can 

be used as a proactive management tool to restore degraded riparian 

habitat. Beaver were abundant in forested, shrub–steppe, and some hot 

desert habitats in the western United States until fur trapping decimated populations. Ranchers followed trappers in settlement of the 

West, and immense numbers of sheep and cattle subjected newly beaverfree riparian areas to intense overgrazing. Overgrazing stripped streambanks of soil-binding vegetation, and channels responded with accelerated erosion and severe downcutting (see Elliott et al. [1999] for a 

discussion of possible mechanisms to explain observed channel incision). Mechanical restoration and revegetation (willow, cottonwood) 

of incised channels can be expensive, labor-intensive, and often 
of herbaceous aquatic and riparian vegetation for summer beaver food 

and to permit establishment and growth of willow or other woody riparian vegetation for winter beaver food. Aspen, cottonwood, or willow 

can be provided at reintroduction sites, or where beaver have initiated 

dam building on their own, to encourage beaver to remain at the site 

and to provide them with stronger dam-building material, which might 

otherwise be lacking (Apple et al. 1985). In some cases where overwinter food is lacking, beaver may subsist on herbaceous vegetation 

long enough to build dams and ponds. These features may initiate a 

positive riparian response, which stimulates growth of willow or other 

woody vegetation suitable as winter food. A winter food cache provides 

beaver with more permanent habitat and the ability to successfully raise 

young. Thus, beaver can create a positive feedback mechanism by temporarily expanding into marginal habitat (naturally or by introduction), 

improving conditions for the establishment and survival of woody riparian vegetation, and persisting long enough to raise young, which can 

disperse to new marginal habitat. 

Beaver restoration in western riparian areas may also help control 

tamarisk, an invasive woody species (Fig. 15.4). In northwestern Colorado, beaver used tamarisk, sagebrush, and greasewood (Sarcobatus 

vermiculatus) as building material for a series of dams, which coincided 

with increase in the distribution and abundance of coyote willow (S. exigua) relative to tamarisk (B. W. Baker, unpublished data). A similar 

response was observed on the Zuni Indian Reservation in New Mexico 

following the relocation of 23 beaver to seven restoration sites (Albert 

and Trimble 2000). As beaver selectively cut vegetation and impound 

water and sediment behind dams, they alter conditions driving establishment and survival in riparian plant communities. Thus, beaver may 

create a competitive advantage for willow relative to tamarisk in some 

riparian systems, although specific mechanisms need further study at 

various spatial and temporal scales (B. W. Baker, unpublished data). 

Population Estimation. Population density of beaver is usually expressed as number of colonies or individuals in areal or linear units. 

Areal estimates are more appropriate where wetlands are diffuse and 

linear estimates are better where beaver habitat is limited to welldefined watercourses. Estimates of number of individuals are often 

derived from colony counts, but are not meaningful unless the mean 

number of beaver per colony is based on local data and not the general literature. Multiplying number of colonies by the general average 

of 5 or 6 beaver per colony only adds false precision to population 

estimates. 

Estimates of mean colony size are very difficult to obtain and 

vary temporally and spatially, but are important in setting harvest quotas (Novak 1987). Colony size can be estimated by using night-vision 

scopes to count beaver as they move about their territory, driving beaver 

from their lodges using smoke or dogs, draining the pond and dismantling the lodge (not recommended), attempting to trap all the beaver in a 

colony (difficult to accomplish, thus a conservative estimate), and employing models that use age and reproductive data from populations of 

trapped beaver (Novak 1987) or data on the interactions among natality, 

mortality, and dispersal (Bishir et al. 1983). 

Size of the food cache may be a useful predictor of colony size, but 

more research is needed to better understand relationships, as studies in 

different regions have been equivocal. In Montana, aerial cache surveys 

of prairie rivers located about 90% of caches, but colony size varied 

among years and areas. Thus, cache counts alone are not good predictors 

of population size or trend (Swenson et al. 1983). Estimates of cache size 

were a significant predictor of colony size in a Montana study (EasterPilcher 1990). This was not the case in a Wyoming study, however, 

perhaps due to variation in cache-building behavior among different 

age cohorts (Osmundson and Buskirk 1993). 

F 15.4. A conceptual model of the use of the beaver (Castor canadensis) activity as a possible mechanism for riparian 

restoration in shrub–steppe ecosystems. 
beaver (reviews by Hill 1982; Novak 1987). For example, aerial surveys only located 41 of 146 ground-located beaver colonies in Kansas 

riverine habitat, where beaver lived in bank dens and did not build food 

caches (Robel and Fox 1993). 

Various combinations of aerial photography, aerial videography, 

and geographic information systems (GIS) can also be used to survey 

beaver populations and evaluate habitat conditions. Aerial photographs 

can be used as a reconnaissance aid to locate beaver habitat in remote 

locations for later ground or aerial survey; to map locations of dams, 

ponds, and lodges via photointerpretation methods; to find and/or plot 

colony locations during ground surveys (<1:3000-scale best); and to 

create overlays of beaver colony locations and habitat features that can 

be digitized into a GIS (Parsons and Brown 1978; Novak 1987; Baker 

et al. 1992; Werth and Boyd 1997). A GIS is essential for some types of 

landscape-level analysis of beaver habitat and may be better than manual methods for others, depending on costs and technical requirements 

(Johnston and Naiman 1990c). Global positioning systems (GPS) allow users to plot exact locations of active or inactive lodges and dens, 

which can be integrated with GIS systems to develop highly accurate 

beaver habitat models or monitoring programs. Aerial videography via 

a helicopter-mounted video camera may be useful for locating and monitoring beaver populations, especially in meandering riparian systems 

that are difficult to observe from low-level, fixed-winged aircraft (B. W. 

Baker, pers. obs.). Video has the advantage of instant availability on 

return from the flight and can be integrated with on-board GPS systems 

to create georeferenced data for computer analysis; however, videography is less useful than aerial photography for creating images for use 

in the field. 

Sex Determination. Sex of beaver carcasses can be determined by the 

presence of the baculum and testes in males and the uterus in females, 

but the lack of any obvious external sex characteristics makes sex determination in live animals difficult (Novak 1987). The sex of live adult 

beaver can be determined by probing the cloaca or palpating the abdominal region for the baculum and testes, by noting the presence of 

four enlarged pectoral mammae in pregnant females (after 2 months), 

by giving beaver the anesthetic combelen (which causes the penis to 

lapse into the cloaca), by detecting Barr bodies in blood smears, and 

by using radiographs that reveal the presence of the baculum (review 

by Novak 1987). Each of these methods has some level of uncertainty 

or practical constraints for adult beaver and is especially difficult for 

young (reviews by Novak 1987; Schulte et al. 1995). A recently developed technique uses the color and viscosity of anal gland secretion to 

determine the sex of adult and juvenile beaver. This method produced 

relatively accurate and consistent results from three different regions in 

New York, which suggests it may have general field application for sex 

identification in beaver (Schulte et al. 1995). 

Age Estimation. Characteristics of tooth eruption and annual cementum layers have been in standard use for age determination since the 

1960s (reviews by Hill 1982; Novak 1987). A refinement in the cementum layer method used the independent variables cementum length and 

noncementum length to fairly accurately predict ages for a sample of 28 

beaver (≥4 years old) with an exponential model, suggesting practical 

application in cases where more exact data are not necessary (Houston 

and Pelton 1995). Techniques for estimating age of live beaver are generally less accurate than the cementum method used for carcasses. The 

most common methods have used weight and skull measures, despite 

large error rates (Novak 1987; Hartman 1992). A refinement using regression models to estimate the age of live beaver based on live weight, 

tail width, and tail length was useful in identifying three age classes: 

kits, yearlings, and ≥ 2-year olds (Van Deelen 1994). A technique using 

seep bas ad aey aps ae sesaow wae. oae sucase

type traps, which hold the beaver in a wire cage above water until 

released. Hancock traps are usually more effective than Bailey traps 

and are preferred in most situations (Novak 1987). Snares are cheap, 

light, and easy to set. They permit trappers to increase capture rates 

by saturating an area with traps, but have a greater mortality rate than 

Hancock traps due to increased risk of predation, entanglement leading to suffocation, and drowning (Hill 1982; McKinstry and Anderson 

1998). Box traps baited with aspen and scent lure were effective for 

all age classes in spring and early summer when set along shoreline 

travel lanes in Massachusetts (C. Henner, pers. commun., 2001). In all 

cases, multiple traps per trapnight percolony will increase the likelihood of trapping all colony members or specific targeted individuals 

before colony members become trap shy. In some cases, beaver can be 

captured by nets or by hand after being flushed from lodges or dens 

by dogs or other means (Hill 1982; Rosell and Hovde 2001). In large 

river systems or lakes, surface-swimming beaver can be captured using 

a dip net. A dive net can be pushed down over the top of swimming 

beaver in shallow water, after locating them with the aid of spotlights 

and headlights from a motorboat (Rosell and Hovde 2001). 

Tagging. Beaver can be individually marked with ear tags, neck collars, tail tags, and other methods (Novak 1987). Beaver may retain ear 

tags for several years, but retention rates have varied greatly among 

studies (review by Novak 1987). The tail can be marked with holes, 

notches, rivets, waterproof paint, branding, cryobranding with liquid 

nitrogen, and cattle ear tags (B. W. Baker, pers. obs.), and the fur can 

be bleached or dyed. Hind feet webs also can be tattooed or punched 

to individually mark beaver. Subcutaneously placed passive integrated 

transponder tags can positively identify recaptured beaver as well as 

free-ranging beaver, which can be scanned with a tag reader as they 

enter or exit burrows or lodges (although this method has not been field 

tested). These techniques all vary in their effectiveness and in trauma 

caused to beaver during and after marking, important considerations 

when selecting an appropriate marking technique. 

Telemetry. Beaver are nocturnal and difficult to observe, so telemetry 

is often valuable in studies of their behavior and movements. However, 

transmitter attachment has been problematic. Neck collars often slip 

off because beaver have a thick neck relative to head size, and tail collars slip off if tail size decreases following release (B. W. Baker, pers. 

obs.). Free-floating intraperitoneal transmitter implants have proven 

successful in several studies, although their range can be relatively 

short (ground-to-ground signal of 0.1 km for beaver inside burrows 

and 2 km for active beaver; Davis et al. 1984). Implanted transmitters become tightly encapsulated with necrotic fibrous tissue and may 

be well tolerated by beaver (Guynn et al. 1987). Implants have been 

performed via dorsal (Davis et al. 1984) and ventrolateral (Wheatley 

1997d) incisions. Although both techniques have been successful, the 

ventrolateral method appears to involve less risk to the animal. 

Tail-mounted transmitters have shown variable success in 

Wyoming (Bothmeyer et al. 2002), Massachusetts (C. Henner, pers. 

commun., 2001), and Colorado (B. W. Baker, pers. obs.). This method 

uses a livestock ear tag transmitter attached to the dorsal surface of a 

beaver’s tail. Dimensions and weight of tail-mounted transmitters can 

be designed to fit beaver tails of various sizes (kits, adults) and allow 

for variation in tail thickness. Durability and attachment effects (e.g., 

tearing the tail) of tail-mounted transmitters have yet to be determined, 

although preliminary evidence suggests short retention time for a relatively high percentage of individuals (B. W. Baker, pers. obs.). 

Reintroduction. The first step in any reintroduction program should be 

to determine the purpose and feasibility of attempting to establish new 
able data, but also may be based on mathematical simulation models. 

South et al. (2000) developed a spatially explicit model to evaluate the 

proposed reintroduction of Eurasian beaver to Scotland. Their model 

simulated births and deaths of individuals and dispersal between habitat 

patches based on a land cover map and predicted that a reintroduction 

of 20 beaver would be sufficient to establish an initial population that 

would eventually expand and fill suitable habitat. 

Most beaver do not stay at release sites and may move great distances following release. Average dispersal distances were 14.6 km in 

a North Dakota study, 16.7 km in a Colorado study, 11.7 km in a Maine 

study, 18 km in a Quebec study, and 7.4 km for beaver transplanted 

to streams and 3.2 km for beaver transplanted to lakes in a Wisconsin 

study (review by Novak 1987). Beaver can sometimes be encouraged 

to stay at specific release sites by providing aspen or other preferred 

species as food and building material or creating a base for a beaver 

dam by placing posts, wire fencing, silt-retaining fabric, rock, or other 

material (Apple et al. 1985; B. W. Baker, pers. obs.). 

Survival of relocated beaver can depend on suitability of available 

habitat, timing of release (late summer in areas that freeze allows time 

to establish ponds and food cache), sex, age, composition, and number released (entire family units may improve establishment success), 

predation, and disease. In a study of 57 released Eurasian beaver in the 

Netherlands, 19 animals were found dead within the first year and 50% 

of these had died of infectious diseases (Yersinia pseudotuberculosis, 

Y. enterocolitica, Leptospirosis, and others) (Nolet et al. 1997). Stress 

during handling may increase risk of disease following release. Vaccination against likely disease agents and attention to animal hygiene 

before release may reduce mortality. Holding beaver in a cool, damp environment, providing adequate food and water, and minimizing length 

of captivity should improve survival following release (Novak 1987). 

RESEARCH NEEDS 

Beaver research has evolved from descriptions of beaver and their habitat to attempts to better understand mechanisms that explain behavior, 

population structure, and their keystone role in ecosystem structure and 

function. New knowledge about beaver will likely come from crossdiscipline studies that stretch the boundaries of our already rich literature base on beaver. For example, a better understanding of the role of 

beaver as geological agents in the formation of alluvial floodplain valleys begs for the integration of the ecological sciences with new methods 

in geology and geomorphology, such as dating of buried organic layers 

that represent beaver dams and pond sediments. An important research 

need is to develop independent lines of evidence about how beaver 

affect ecosystem structure and function over the full range of ecological conditions inhabited by beaver, especially in the less well-known 

communities such as southeastern forests, western shrub–steppe, and 

desert grasslands. These studies should include the sequential events 

of development and abandonment that make up the life history of a 

beaver pond ecosystem. In South America and Europe, beaver are an 

invasive species with an ecological role that likely will require a different level of understanding than in their native North American habitat. 

The economic values of beaver wetlands in storing water, improving 

water quality, restoring wetland function, and mitigating development 

will be of critical importance as human populations expand and strain 

the land’s ability to absorb their impact. The human dimensions of 

beaver management and control methods need improved understanding to better educate a public that is becoming more removed from 

the land and more inclined to use legislative or judicial means rather 

than the judgment of wildlife professionals to manage wildlife populations. Techniques need further refinement to more effectively estimate 

beaver populations, determine sex and age of live beaver in the field, and 

of Wild Mammals of North America for a more thorough coverage of 

earlier work, and the following reviews and annotated bibliographies: 

Denney (1952), Yeager and Hay (1955), Jenkins and Busher (1979), 

Hodgdon and Larson (1980), Novak (1987), Medin and Torquemada 

(1988), and Olson and Hubert (1994). 

ACKNOWLEDGMENTS 

We are grateful to David Mitchell for compiling relevant literature, 

Dale Crawford for the preparing the artwork in Figures 15.3 and 15.4, 

and Stewart Breck, Doug Smith, and Butch Roelle for reviewing the 

manuscript. Funding was provided by the U.S. Geological Survey, Fort 

Collins Science Center, Fort Collins, Colorado. 

LITERATURE CITED 

Aeschbacher, A., and G. Pilleri. 1983. Observation on the building behaviour 

of the Canadian beaver (Castor canadensis) in captivity. Pages 83–98 in 

G. Pilleri, ed. Investigations on beaver, Vol. 1. Brain Anatomy Institute, 

Berne, Switzerland. 

Albert, S., and T. Trimble. 2000. Beavers are partners in riparian restoration on 

the Zuni Indian Reservation. Ecological Restoration 18:87–92. 

Aldous, S. E. 1938. Beaver food utilization studies. Journal of Wildlife Management 2:215–22. 

Aleksuik, M. 1970a. The function of the tail as a fat storage depot in the beaver. 

(Castor canadensis Kuhl). Journal of Mammalogy 51:145–48. 

Aleksiuk, M. 1970b. The seasonal food regime of arctic beaver. Ecology 51:264– 

70. 

Aleksiuk, M., and I. Cowan. 1969. Aspects of seasonal energy expenditure 

in the beaver (Castor canadensis). Canadian Journal of Zoology 47:471– 

81. 

Allen, A. W. 1983. Habitat suitability index models: Beaver. (FWS/OBS82/10.30, rev.). U.S. Department of the Interior, Fish and Wildlife Service. 

Apple, L. L., B. H. Smith, J. D. Dunder, and B. W. Baker. 1985. The use 

of beavers for riparian/aquatic habitat restoration of cold desert, gullycut stream systems in southwestern Wyoming. Pages 123–30 in G. Pilleri, ed. Investigations on beaver, Vol. 4. Brain Anatomy Institute, Berne, 

Switzerland. 

Baker, B. W., and B. S. Cade. 1995. Predicting biomass of beaver food from 

willow stem diameters. Journal of Range Management 48:322–26. 

Baker, B. W., D. L. Hawksworth, and J. G. Graham. 1992. Wildlife habitat response to riparian restoration on the Douglas Creek watershed. Proceedings 

of the Annual Conference of the Colorado Riparian Association 4:62–80. 

Barnes, D. M., and A. U. Mallik. 1996. Use of woody plants in construction of 

beaver dams in northern Ontario. Canadian Journal of Zoology 74:1781– 

86. 

Barnes, D. M., and A. U. Mallik. 1997. Habitat factors influencing beaver dam 

establishment in a northern Ontario watershed. Journal of Wildlife Management 61:1371–77. 

Barnes, W. J., and E. Dibble. 1988. The effects of beaver in riverbank forest 

succession. Canadian Journal of Botany 66:40–44. 

Basey, J. M. 1999. Foraging behavior of beaver (Castor canadensis), plant secondary compounds, and management concerns. Pages 129–46 in P. E. 

Busher and R. M. Dzieciolowski, eds. Beaver protection, management, 

and utilization in Europe and North America. Kluwer Academic/Plenum, 

New York. 

Basey, J. M., S. H. Jenkins, and P. E. Busher. 1988. Optimal central-place foraging 

by beaver: Tree size selection in relation to defensive chemicals of quaking 

aspen. Oecologia 76:278–82. 

Basey, J. M., S. H. Jenkins, and G. C. Miller. 1990. Food selection by beavers in 

relation to inducible defenses of Populus tremuloides. Oikos 59:57–62. 

Beier, P., and R. H. Barrett. 1987. Beaver habitat use and impact in Truckee 

River Basin, California. Journal of Wildlife Management 51:794–99. 

Belovsky, G. E. 1984. Summer diet optimization by beaver. American Midland 

Naturalist 111:209–22. 

Bergerud, A. T., and D. R. Miller. 1977. Population dynamics of Newfoundland 

beaver. Canadian Journal of Zoology 55:1480–92. 
y (

canadensis). Anatomischer Anzeiger 151:381–91. 

Bishir, J., R. A. Lancia, and H. E. Hodgdon. 1983. Beaver family organization: Its 

implications for colony size. Pages 105–13 in G. Pilleri, ed. Investigations 

on beavers, Vol. 4, Brain Anatomy Institute, Berne, Switzerland. 

Boyce, M. S. 1981a. Habitat ecology of an unexploited population of beaver 

in interior Alaska. Pages 155–86 in J. A. Chapman and D. Pursley, 

eds. Proceedings of the worldwide furbearer conference. Frostburg, 

MD. 

Boyce, M. S. 1981b. Beaver life-history responses to exploitation. Journal of 

Applied Ecology 18:749–53. 

Brady, C. A., and G. E. Svendsen. 1981. Social behavior in a family of beaver, 

Castor canadensis. Biology of Behaviour 6:99–114. 

Breck, S. W. 2001. The effects of flow regulation on the population biology and 

ecology of beavers in northwestern Colorado. Ph.D. Dissertation, Colorado 

State University, Fort Collins. 

Brown, D. J., W. A. Hubert, and S. H. Anderson. 1996. Beaver ponds create 

wetland habitat for birds in mountains of southeastern Wyoming. Wetlands 

16:127–32. 

Bryce, G. 1904. The remarkable history of the Hudson Bay Company. Reprint, 

1968. Burt Franklin, New York. 

Buech, R. R. 1984. Ontogeny and diurnal cycle of fecal reingestion in the North 

American beaver (Castor canadensis). Journal of Mammalogy 65:347– 

50. 

Buech, R. R. 1985. Beaver in water impoundments: Understanding a problem 

of water-level management. Pages 95–105 in D. M. Knighton, Comp., Water impoundments for wildlife: A habitat management workshop (General 

Technical Report NC-100). U.S. Department of Agriculture, Forest Service. 

Buech, R. R., and D. J. Rugg. 1995. Biomass of food available to beavers on five 

Minnesota shrubs (Research Paper NC-326). U.S. Department of Agriculture, Forest Service, North Central Forest Experiment Station. 

Busher, P. E. 1983. Interactions between beavers in a montane population in 

California. Acta Zoologica Fennica 174:109–10. 

Busher, P. E. 1987. Population parameters and family composition of beaver in 

California. Journal of Mammalogy 68:860–64. 

Busher, P. E., and P. J. Lyons. 1999. Long-term population dynamics of the 

North American beaver, Castor canadensis, on Quabbin Reservation, Massachusetts, and Sagehen Creek, California. Pages 147–60 in P. E. Busher 

and R. M. Dzieciolowski, eds. Beaver protection, management, and utilization in Europe and North America. Kluwer Academic/Plenum, New 

York. 

Butts, W. L. 1992. Changes in local mosquito fauna following beaver (Castor 

canadensis) activity: An update. Journal of the American Mosquito Control 

Association 8:331–32. 

Cahn, A. R. 1932. Records and distribution of the fossil beaver, Castoroides 

ohioensis. Journal of Mammalogy 13:229–41. 

Cottrell, T. R. 1995. Willow colonization of Rocky Mountain mires. Canadian 

Journal of Forest Research 25:215–22. 

Davis, J. R., A. F. Von Recum, D. D. Smith, and D. C. Guynn, Jr. 1984. Implantable 

telemetry in beaver. Wildlife Society Bulletin 12:322–24. 

Davis, J. R., D. C. Guynn, Jr., and G. W. Gatlin. 1994. Territorial behavior 

of beaver in the Piedmont of South Carolina. Proceedings of the Annual 

Conference of the Southeastern Association of Fish and Wildlife Agencies 

48:152–61. 

Davis, W. B. 1940. Critical notes on the Texas beaver. Journal of Mammalogy 

21:84–86. 

Deems, E. F., and D. Pursley. 1978. North American furbearers: Their management, research, and harvest status in 1976. University of Maryland Press, 

College Park, Maryland. 165 pp. 

Denney, R. N. 1952. A summary of North American beaver management, 1946– 

1948 (Current Report 28). Colorado Game and Fish Department, Denver. 

Dieter, C. D., and T. R. McCabe. 1989. Factors influencing beaver lodgesite selection on a prairie river. American Midland Naturalist 122:408– 

11. 

Donkor, N. T., and J. M. Fryxell. 1999. Impact of beaver foraging on structure 

of lowland boreal forests of Algonquin Provincial Park, Ontario. Forest 

Ecology and Management 118:83–92. 

Doucet, C. M., and J. M. Fryxell. 1993. The effect of nutritional quality on forage 

preference by beavers. Oikos 67:201–8. 

gy 

Dyck, A. P., and R. A. MacArthur. 1993. Daily energy requirements of beaver 

(Castor canadensis) in a simulated winter microhabitat. Canadian Journal 

of Zoology 71:2131–35. 

Easter-Pilcher, A. 1990. Cache size as an index to beaver colony size in northwestern Montana. Wildlife Society Bulletin 18:110–13. 

Elliott, J. G., A. C. Gellis, and S. B. Aby. 1999. Evolution of arroyos: Incised 

channels of the southwestern United States. Pages 153–85 in S. E. Darby 

and A. Simon, eds. Incised river channels: Processes, forms, engineering 

and management. John Wiley, New York. 

Enck, J. W., N. A. Connelly, and T. L. Brown. 1997. Acceptance of beaver 

and actions to address nuisance beaver problems in New York. Human 

Dimensions of Wildlife 2:60–61. 

Engelhart, A., and D. Muller-Schwarze. 1995. Responses of beaver (Castor 

canadensis Kuhl) to predator chemicals. Journal of Chemical Ecology 

21:1349–64. 

Fischer, T. V. 1985. The subplacenta of the beaver (Castor canadensis). Placenta 

6:311–21. 

Friley, C. E. Jr. 1949. Use of the baculum in age determination of Michigan 

beaver. Journal of Mammalogy 30:261–65. 

Fryxell, J. M. 1992. Space use by beaver in relation to resource abundance. 

Oikos 64:474–78. 

Fryxell, J. M., and C. M. Doucet. 1990. Provisioning time and central-place 

foraging in beaver. Canadian Journal of Zoology 69:1308–13. 

Fryxell, J. M., S. M. Vamosi, R. A. Walton, and C. M. Doucet. 1994. Retention 

time and the functional response of beavers. Oikos 71:207–14. 

Garrison, G. C. 1967. Pollen stratigraphy and age of an early postglacial beaver 

site near Columbus, Ohio. Ohio Journal of Science 67:96–105. 

Grinnell, J., J. S. Dixon, and J. M. Linsdale. 1937. Fur bearing mammals of 

California, their natural history, systematic status, and relations to man. 

University of California Press, Berkeley. 

Grover, A. M., and G. A. Baldassarre. 1995. Bird species richness within beaver 

ponds in south-central New York. Wetlands 15:108–18. 

Gunson, J. R. 1970. Dynamics of the beaver of Saskatchewan’s northern forest. 

M.S. Thesis, University of Alberta, Edmonton, Canada. 

Gurnell, A. M. 1998. The hydrogeomorphological effects of beaver dambuilding activity. Progress in Physical Geography 22:167–89. 

Guynn, D. C., Jr., J. R. Davis, and A. F. Von Recum. 1987. Pathological potential of intraperitoneal transmitter implants in beaver. Journal of Wildlife 

Management 51:605–6. 

Hakala, J. B. 1952. The life history and general ecology of the beaver (Castor 

canadensis Kuhl) in interior Alaska. M.S. Thesis, University of Alaska, 

Fairbanks. 

Hall, E. R. 1981. The mammals of North America, Vol. 2, 2nd ed., John Wiley, 

New York. 

Hammerson, G. A. 1994. Beaver (Castor canadensis): Ecosystem alterations, 

management, and monitoring. Natural Areas Journal 14:44–57. 

Hartman, G. 1992. Age determination of live beaver by dental x-ray. Wildlife 

Society Bulletin 20:216–20. 

Hilfiker, E. L. 1991. Beavers: Water, wildlife and history. Windswept Press, 

Interlaken, NJ. 

Hill, E. P. 1974. Trapping beaver and processing their fur (Zoology and Entomology Department Series, Alabama Cooperative Wildlife Research Unit, 

No. 1). Agricultural Experiment Station, Auburn University, Auburn, AL. 

Hill, E. P. 1976. Control methods for nuisance beaver in the southeastern United 

States. Pages 85–98 in Proceedings of the seventh vertebrate pest control 

conference. 

Hill, E. P. 1982. Beaver (Castor canadensis). Pages 256–81 in J. A. Chapman and 

G. A. Feldhamer, eds. Wild mammals of North America. Johns Hopkins 

University Press, Baltimore. 

Hill, E. P., and N. S. Novakowski. 1984. Beaver management and economics in 

North America. Acta Zoologica Fennica 172:259–62. 

Hillman, G. R. 1998. Flood wave attenuation by a wetland following a beaver 

dam failure on a second order boreal stream. Wetlands 18:21–34. 

Hodgdon, H. E. 1978. Social dynamics and behavior within an unexploited 

beaver (Castor canadensis) population. Ph.D. Dissertation, University of 

Massachusetts, Amherst. 

Hodgdon, H. E., and R. A. Lancia. 1983. Behavior of the North American beaver, 

Castor canadensis. Acta Zoologica Fennica 174:99–103. 
gy p

of Wildlife Management 13:412–14. 

Hodgdon, K. W., and J. J. Hunt. 1953. Beaver management in Maine (Maine 

Game Division Bulletin 3). 

Houston, A. E., and M. R. Pelton. 1995. Premolar cementum and noncementum lengths as potential indicators of age for beavers, Castor canadensis 

(Rodentia: Castoridae). Brimleyana 22:67–72. 

Houston, A. E., E. R. Buckner, and J. C. Rennie. 1992. Reforestation of drained 

beaver impoundments. Southern Journal of Applied Forestry 16:151– 

55. 

Houston, A. E., M. R. Pelton, and R. Henry. 1995. Beaver immigration into a 

control area. Southern Journal of Applied Forestry 19:127–30. 

Howard, R., and J. S. Larson. 1985. A stream habitat classification system for 

beaver. Journal of Wildlife Management 49:19–25. 

Ingle-Sidorowicz, H. M. 1982. Beaver increase in Ontario. Result of changing 

environment. Mammalia 46:168–75. 

Jellison, W. L., G. M. Kohls, W. J. Butler, and J. A. Weaver. 1942. Epizootic 

tularemia in the beaver, Castor canadensis, and the contamination of stream 

water with Pasteurella tularensis. American Journal of Hygiene 36:168–82. 

Jenkins, S. H. 1979. Seasonal and year-to-year differences in food selection by 

beavers. Oecologia 44:112–16. 

Jenkins, S. H. 1980. A size distance relation in food selection by beavers. Ecology 

61:740–46. 

Jenkins, S. H. 1981. Problems, progress, and prospects in studies of food selection by beaver. Pages 559–79 in J. A. Chapman and D. Pursley, eds. 

Proceedings of the worldwide furbearer conference. Frostburg, MD. 

Jenkins, S. H., and P. E. Busher. 1979. Castor canadensis. Mammalian Species 

120:1–8. 

Jensen, P. G., P. D. Curtis, and D. L. Hamelin. 1999. Managing nuisance beaver 

along roadsides: A guide for highway departments. Media and Technology 

Services Resource Center, Cornell University, Ithaca, NY. 

Johnston, C. A., and R. J. Naiman. 1987. Boundary dynamics at the aquatic– 

terrestrial interface: The influence of beaver and geomorphology. Landscape Ecology 1:47–57. 

Johnston, C. A., and R. J. Naiman. 1990a. Aquatic patch creation in relation to 

beaver population trends. Ecology 71:1617–21. 

Johnston, C. A., and R. J. Naiman. 1990b. Browse selection by beaver: Effects on 

riparian forest composition. Canadian Journal of Forest Research 20:1036– 

43. 

Johnston, C. A., and R. J. Naiman. 1990c. The use of geographic information 

systems to analyze long-term landscape alteration by beaver. Landscape 

Ecology 4:5–19. 

Jones, C. G., J. H. Lawton, and M. Shachak. 1997. Positive and negative effects 

of organisms as physical ecosystem engineers. Ecology 78:1946–57. 

Keast, A., and M. G. Fox. 1990. Fish community structure, spatial distribution 

and feeding ecology in a beaver pond. Environmental Biology of Fishes 

27:201–14. 

Kindschy, R. R. 1985. Response of red willow to beaver use in southeastern 

Oregon. Journal of Wildlife Management 49:26–28. 

Kindschy, R. R. 1989. Regrowth of willow following simulated beaver cutting. 

Wildlife Society Bulletin 17:290–94. 

King, S. L., B. D. Kneeland, and J. L. Moore. 1998. Beaver lodge distributions 

and damage assessments in a forested wetland ecosystem in the southern 

United States. Forest Ecology and Management 108:1–7. 

Kowalski, K. 1976. Mammals, an outline of theriology. Polis, Warsaw. 

Krueger, H. O. 1985. Avian response to mountainous shrub–willow riparian systems in southeastern Wyoming. Ph.D. Dissertation, University of Wyoming, 

Laramie. 

Lahti, S., and M. Helminen. 1974. The beaver Castor fiber (L.) and Castor 

canadensis (Kuhl) in Finland. Acta Theriologica 19:177–89. 

Lancia, R. A., W. E. Dodge, and J. S. Larson. 1982. Winter activity patterns of 

two radio-marked beaver colonies. Journal of Mammalogy 63:598–606. 

Lancia, R. A., and H. E. Hodgdon. 1983. Observations on the ontogeny of behavior of hand-reared beaver (Castor canadensis). Acta Zoologica Fennica 

174:117–19. 

Landin, J. A. B. 1980. Estado actual del ‘Castor’ (Castor canadensis mexicanus) 

en el Estado de Nuevo Leon, Mexico. Pages 309–14 in Proceedings of 

the Inventarios de Recursos de Zonas Aridas. La Paz, B.C.S., Mexico [in 

Spanish with English summary]. 

g

Leopold, A. S. 1959. Wildlife of Mexico, the game birds and mammals. University of California Press, Berkeley. 

Lizarralde, M. S. 1993. Current status of the introduced beaver (Castor canadensis) population in Tierra del Fuego, Argentina. Ambio 22:351–58. 

Lizotte, R. E., Jr. 1994. Reproductive biology of beaver (Castor canadensis) at 

Old Hickory Lake in middle Tennessee. Journal of the Tennessee Academy 

of Science 69:23–26. 

Loker, C. A., D. J. Decker, and S. J. Schwager. 1999. Social acceptability of 

wildlife management actions in suburban areas: 3 cases from New York. 

Wildlife Society Bulletin 27:152–59. 

Mahoney, J. M., and H. I. Rosenberg. 1981. Anatomy of the tail of the beaver 

(Castor canadensis). Canadian Journal of Zoology 59:390–99. 

Maret, T. J., M. Parker, and T. E. Fannin. 1987. The effect of beaver ponds on 

the nonpoint source water quality of a stream in southwestern Wyoming. 

Water Resources 21:263–68. 

Martinsen, G. D., E. M. Driebe, and T. G. Whitman. 1998. Indirect interactions 

mediated by changing plant chemistry: Beaver browsing benefits beetles. 

Ecology 79:192–200. 

McCall, T. C., T. P. Hodgman, D. R. Diefenbach, and R. B. Owen, Jr. 1996. Beaver 

populations and their relation to wetland habitat and breeding waterfowl in 

Maine. Wetlands 16:163–72. 

McComb, W. C., J. R. Sedell, and T. D. Buchholz. 1990. Dam-site selection by 

beavers in an eastern Oregon basin. Great Basin Naturalist 50:273–81. 

McDowell, D. M., and R. J. Naiman. 1986. Structure and function of a benthic invertebrate stream community as influenced by beaver (Castor canadensis). 

Oecologia 68:481–89. 

McGinley, M. A., and T. G. Whitman. 1985. Central place foraging by beaver 

(Castor canadensis): A test of foraging predictions and the impact of selective feeding on the growth form of cottonwoods (Populus fremontii). 

Oecologia 66:558–62. 

McKab, B. K. 1963. A model of the energy budget of a wild mouse. Ecology 

44:521–32. 

McKinstry, M. C., and S. H. Anderson. 1998. Using snares to live-capture beaver, 

Castor canadensis. Canadian Field-Naturalist 112:469–73. 

McKinstry, M. C., and S. H. Anderson. 1999. Attitudes of private- and publicland managers in Wyoming, USA, toward beaver. Environmental Management 23:95–101. 

McKinstry, M. C., P. Caffrey, and S. H. Anderson. 2001. The importance of 

beaver to wetland habitats and waterfowl in Wyoming. Journal of the American Water Resources Association 37:1571–77. 

McRae, G., and C. J. Edwards. 1994. Thermal characteristics of Wisconsin 

headwater streams occupied by beaver: Implications for brook trout habitat. 

Transactions of the American Fisheries Society 123:641–56. 

Medin, D. E., and W. P. Clary. 1990. Bird populations in and adjacent to a beaver 

pond ecosystem in Idaho (Research Paper INT-432). U.S. Department of 

Agriculture, Forest Service, Intermountain Research Station. 

Medin, D. E., and W. P. Clary. 1991. Small mammals of a beaver pond ecosystem 

and adjacent riparian habitat in Idaho (Research Paper INT-445). U.S. Department of Agriculture, Forest Service, Intermountain Research Station. 

Medin, D. E., and K. E. Torquemada. 1988. Beaver in western North America: An 

annotated bibliography, 1966 to 1986 (General Technical Report INT-242). 

U.S. Department of Agriculture, Forest Service, Intermountain Research 

Station. 

Meentemeyer, R. K., and D. R. Butler. 1999. Hydrogeomorphic effects of beaver 

dams in Glacier National Park, Montana. Physical Geography 20:436– 

46. 

Merendino, M. T., G. B. McCullough, and N. R. North. 1995. Wetland availability and use by breeding waterfowl in southern Ontario. Journal of Wildlife 

Management 59:527–32. 

Miller, J. E., and G. K. Yarrow. 1994. Beaver. Pages B1–11 in S. E. Hygnstrom, 

R. M. Timm, and G. E. Larson, eds. Prevention and control of wildlife 

damage. University of Nebraska Press, Lincoln. 

Molini, J. J., R. A. Lancia, J. Bishir, and H. E. Hodgdon. 1980. A stochastic 

model of beaver population growth. Pages 1215–45 in J. A. Chapman 

and D. Pursley, eds. Proceedings of the worldwide furbearer conference. 

Frostburg, MD. 

Morner, T. 1992. The ecology of tularemia. Revue Scientifique et Technique 

O.I.E. (Office International des Epizooties) 11:1123–30. 
Muller-Schwarze, D., S. Heckman, and B. Stagge. 1983. Behavior of freeranging beaver (Castor canadensis) at scent marks. Acta Zoologica Fennica 

174:111–13. 

Muller-Schwarze, D., B. A. Schulte, L. Sun, A. Muller-Schwarze, and C. MullerSchwarze. 1994. Red maple (Acer rubrum) inhibits feeding by beaver (Castor canadensis). Journal of Chemical Ecology 20:2021–34. 

Naiman, R. J., and J. M. Melillo. 1984. Nitrogen budget of a subarctic stream 

altered by beaver (Castor canadensis). Oecologia 62:150–55. 

Naiman, R. J., J. M. Melillo, and J. E. Hobbie. 1986. Ecosystem alteration of 

boreal forest streams by beaver (Castor canadensis). Ecology 67:1254– 

69. 

Naiman, R. J., C. A. Johnston, and J. C. Kelley. 1988. Alteration of North 

American streams by beaver. BioScience 38:753–62. 

Naiman, R. J., G. Pinay, C. A. Johnston, and J. Pastor. 1994. Beaver influences 

on the long-term biogeochemical characteristics of boreal forest drainage 

networks. Ecology 75:905–21. 

Nolet, B. A., S. Broekhuizen, G. M. Dorrestein, and K. M. Rienks. 1997. Infectious diseases as main causes of mortality to beaver Castor fiber after translocation to the Netherlands. Journal of the Zoological Society of 

London 241:35–42. 

Novak, M. 1987. Beaver. Pages 283–312 in M. Novak, J. A. Baker, M. E. 

Obbard, and B. Malloch, eds. Wild furbearer management and conservation 

in North America. Ontario Trappers Association and Ontario Ministry of 

Natural Resources. 

Novakowski, N. S. 1965. Population dynamics of a beaver population in northern latitudes. Ph.D. Dissertation, University of Saskatchewan, Saskatoon, 

Canada. 

Nummi, P. 1992. The importance of beaver ponds to waterfowl broods: An 

experiment and natural tests. Annales Zoologici Fennici 29:47–55. 

Nummi, P., and H. Poysa. 1997. Population and community level responses in 

Anas-species to patch disturbance caused by an ecosystem engineer, the 

beaver. Ecography 20:580–84. 

Olson, R., and W. A. Hubert. 1994. Beaver: Water resources and riparian habitat 

manager. University of Wyoming Press, Laramie. 

Osmundson, C. L., and S. W. Buskirk. 1993. Size of food caches as a predictor 

of beaver colony size. Wildlife Society Bulletin 21:64–69. 

Paine, R. T. 1969. A note on trophic complexity and community stability. American Naturalist 103:91–93. 

Parker, M., F. J. Wood, Jr., B. H. Smith, and R. G. Elder. 1985. Erosional downcutting in lower order riparian ecosystems: Have historical changes been 

caused by removal of beaver? Proceedings of the North American Riparian 

Conference 1:35–38. 

Parsons, G. R., and M. K. Brown. 1978. An assessment of aerial photograph 

interpretation for recognizing potential beaver colony sites. Transactions 

of the Northeast Fish and Wildlife Conference 35:181–84. 

Patenaude, F., and J. Bovet. 1984. Self-grooming and social-grooming in the 

North American beaver, Castor canadensis. Canadian Journal of Zoology 

62:1872–78. 

Payne, N. F. 1975. Trapline management and population biology of Newfoundland beaver. Ph.D. Dissertation, Utah State University, Logan. 

Payne, N. F. 1984. Population dynamics of beaver in North America. Acta 

Zoologica Fennica 172:263–66. 

Potvin, F., L. Breton, C. Pilon, and M. Macquart. 1992. Impact of an experimental 

wolf reduction on beaver in Papineau-Labelle Reserve, Quebec. Canadian 

Journal of Zoology 70:180–83. 

Power, M. E., D. Tilman, J. A. Estes, B. A. Menge, W. J. Bond, L. S. Mills, G. 

Daily, J. C. Castilla, J. Lubchenco, and R. T. Paine. 1996. Challenges in the 

quest for keystones. BioScience 46:609–20. 

Provost, E. E. 1958. Studies on reproduction and population dynamics in beaver. 

Ph.D. Dissertation, State College of Washington, Pullman. 

Provost, E. E. 1962. Morphological characteristics of the beaver ovary. Journal 

of Wildlife Management 26:272–78. 

Rebertus, A. J. 1986. Bogs as beaver habitat in north-central Minnesota. American Midland Naturalist 116:240–45. 

Reese, K. P., and J. D. Hair. 1976. Avian species diversity in relation to beaver 

pond habitats in the Piedmont Region of South Carolina. Proceedings of the 

Annual Conference of the Southeastern Association of Fish and Wildlife 

Agencies 30:437–47. 

ggg (

Leaflet 13.4.7). U.S. Department of Interior, Fish and Wildlife Service, 

Washington, DC. 

Robel, R. J., and L. B. Fox. 1993. Comparison of aerial and ground survey 

techniques to determine beaver colony densities in Kansas. Southwestern 

Naturalist 38:357–61. 

Robel, R. J., L. B. Fox, and K. E. Kemp. 1993. Relationship between habitat 

suitability index values and ground counts of beaver colonies in Kansas. 

Wildlife Society Bulletin 21:415–21. 

Roberts, T. H., and D. H. Arner. 1984. Food habits of beaver in east-central 

Mississippi. Journal of Wildlife Management 48:1414–19. 

Robertson, R. A., and and A. R. Shadle., 1954. Osteologic criteria of age in 

beavers. Journal of Mammalogy 35:197–203. 

Rosell, F., and B. Hovde. 2001. Methods of aquatic and terrestrial netting to 

capture Eurasian beavers. Wildlife Society Bulletin 29:269–74. 

Rothmeyer, S. W., M. C. McKinstry, and S. H. Anderson. 2002. Tail attachment 

of modified ear-tag radio transmitters on beaver. Wildlife Society Bulletin 

30:425–29. 

Ruedemann, R., and W. J. Schoonmaker. 1938. Beaver-dams as geologic agents. 

Science 88:523–25. 

Russell, K. R., C. E. Moorman, J. K. Edwards, B. S. Metts, and D. C. Guynn, Jr. 

1999. Amphibian and reptile communities associated with beaver (Castor 

canadensis) ponds and unimpounded streams in the Piedmont of South 

Carolina. Journal of Freshwater Ecology 14:149–58. 

Rutherford, W. H. 1955. Wildlife and environmental relationships of beaver in 

Colorado forests. Journal of Forestry 53:803–6. 

Safonov, V. G. 1979. Experience of American beaver, Castor canadensis, introduction in Kamchatka. In Game management and fur farming USSR: 

international wildlife congress 14. All Union Research Institute [Abstract 

in English]. 

Schlosser, I. J. 1995. Dispersal, boundary processes, and trophic-level interactions in streams adjacent to beaver ponds. Ecology 76:908–25. 

Schlosser, M. 1902. Extinct beaver (Castor neglectus) from Tertiary of South 

Germany. Palaeontoligische Abhandlungen 9:136. 

Schulte, B. A. 1998. Scent marking and responses to male castor fluid by beavers. 

Journal of Mammalogy 79:191–203. 

Schulte, B. A., and D. Muller-Schwarze. 1999. Understanding North American 

beaver behavior as an aid to management. Pages 109–128 in P. E. Busher 

and R. M. Dzieciolowski, eds. Beaver protection, management, and utilization in Europe and North America. Kluwer Academic/Plenum, New 

York. 

Schulte, B. A., D. Muller-Schwarze, and L. Sun. 1995. Using anal gland secretion to determine sex in beaver. Journal of Wildlife Management 59:614– 

18. 

Seton, E. T. 1929. Lives of game animals, Vol. 4, Part 2, Rodents, etc. Doubleday, 

Doran, Garden City, NY. 

Sieber, J., F. Suchentrunk, and G. B. Hart. 1999. A biochemical–genetic discrimination method for the two beaver species, Castor fiber and Castor 

canadensis, as a tool for conservation. Pages 61–65 in P. E. Busher and 

R. M. Dzieciolowski, eds. Beaver protection, management, and utilization 

in Europe and North America. Kluwer Academic/Plenum, New York. 

Skinner, Q. D., J. E. Speck, Jr., M. Smith, and J. C. Adams. 1984. Stream water quality as influenced by beaver within grazing systems in Wyoming. 

Journal of Range Management 37:142–46. 

Slough, B. G. 1978. Beaver food cache structure and utilization. Journal of 

Wildlife Management 42:644–46. 

Slough, B. G., and R. M. F. S. Sadleir. 1977. A land capability classification 

system for beaver (Castor canadensis Kuhl). Canadian Journal of Zoology 

55:1324–35. 

Smith, D. W., and S. H. Jenkins. 1997. Seasonal change in body mass and size 

of tail of northern beavers. Journal of Mammalogy 78:869–76. 

Smith, D. W., R. O. Peterson, T. D. Drummer, and D. S. Sheputis. 1991. Overwinter activity and body temperature patterns in northern beavers. Canadian Journal of Zoology 69:2178–82. 

Smith, D. W., D. R. Trauba, R. K. Anderson, and R. O. Peterson. 1994. Black 

bear predation on beavers on an island in Lake Superior. American Midland 

Naturalist 132:248–55. 

Smith, M. E., C. T. Driscoll, B. J. Wyskowski, C. M. Brooks, and C. C. Cosentini. 

1991. Modification of stream ecosystem structure and function by beaver 
gpgpgy 

42. 

South, A., S. Rushton, and D. Macdonald. 2000. Simulating the proposed reintroduction of the European beaver (Castor fiber) to Scotland. Biological 

Conservation 93:103–16. 

Stegeman, L. C. 1954. The production of aspen and its utilization by beaver 

on the Huntington Forest. Journal of Wildlife Management 18:348– 

58. 

Sun, L., and D. Muller-Schwarze. 1997. Sibling recognition in the beaver: A 

field test for phenotype matching. Animal Behavior 54:493–502. 

Sun, L., and D. Muller-Schwarze. 1998. Anal gland secretion codes for family 

membership in the beaver. Behavioral Ecology and Sociobiology 44:199– 

208. 

Sun, L., D. Muller-Schwarze, and B. A. Schulte. 2000. Dispersal pattern and effective population size of the beaver. Canadian Journal of Zoology 78:393– 

98. 

Suzuki, N., and W. C. McComb. 1998. Habitat classification models for beaver 

(Castor canadensis) in the streams of the central Oregon coast range. Northwest Science 72:102–10. 

Svendsen, G. E. 1978. Castor and anal glands of the beaver (Castor canadensis). 

Journal of Mammalogy 59:618–20. 

Svendsen, G. E. 1980a. Patterns of scent-mounding in a population of beaver 

(Castor canadensis). Journal of Chemical Ecology 6:133–48. 

Svendsen, G. E. 1980b. Seasonal change in feeding patterns of beaver in southeastern Ohio. Journal of Wildlife Management 44:285–90. 

Svendsen, G. E. 1989. Pair formation, duration of pair-bonds, and mate replacement in a population of beavers (Castor canadensis). Canadian Journal of 

Zoology 67:336–40. 

Swenson, J. E., S. J. Knapp, P. R. Martin, and T. C. Hinz. 1983. Reliability of 

aerial cache surveys to monitor beaver population trends on prairie rivers 

in Montana. Journal of Wildlife Management 47:697–703. 

Terwilliger, J., and J. Pastor. 1999. Small mammals, ectomycorrhizae, and conifer 

succession in beaver meadows. Oikos 85:83–94. 

Van Deelen, T. R. 1994. A field technique for aging live beavers, Castor canadensis. Canadian Field-Naturalist 108:361–63. 

Van Deelen, T. R., and D. H. Pletscher. 1996. Dispersal characteristics of twoyear-old beavers, Castor canadensis, in Western Montana. Canadian FieldNaturalist 110:318–21. 

Vispo, C., and I. D. Hume. 1995. The digestive tract and digestive function in 

the North American beaver. Canadian Journal of Zoology 73:967–74. 

Voight, D. R., G. B. Kolenosky, and D. H. Pimlott. 1976. Changes in summer foods of wolves in central Ontario. Journal of Wildlife Management 

40:663–68. 

Warren, E. R. 1940. A beaver’s food requirements. Journal of Mammalogy 

21:93. 

ygp

use in the taiga of southeastern Manitoba: I. Seasonal variation. Canadian 

Field-Naturalist 111:204–10. 

Wheatley, M. 1997b. Beaver, Castor canadensis, home range size and patterns 

of use in the taiga of southeastern Manitoba: II. Sex, age, and family status. 

Canadian Field-Naturalist 111:211–16. 

Wheatley, M. 1997c. Beaver, Castor canadensis, home range size and patterns of 

use in the taiga of southeastern Manitoba: III. Habitat variation. Canadian 

Field-Naturalist 111:217–22. 

Wheatley, M. 1997d. A new surgical technique for implanting radio transmitters 

in beaver, Castor canadensis. Canadian Field-Naturalist 111:601–6. 

Wigley, T. B., T. H. Roberts, and D. H. Arner. 1983. Reproductive characteristics 

of beaver in Mississippi. Journal of Wildlife Management 47:1172–77. 

Wigley, T. B., T. H. Roberts, and D. H. Arner. 1984. Methods of determining litter 

size in beaver. Proceedings of the Annual Conference of the Southeastern 

Association of Fish and Wildlife Agencies 38:197–200. 

Wilsson, L. 1971. Observations and experiments on the ethology of the European 

beaver (Castor fiber L.). Viltrevy 8:115–266. 

Winkle, P. L., W. A. Hubert, and F. J. Rahel. 1990. Relations between brook 

trout standing stocks and habitat features in beaver ponds in southwestern Wyoming. North American Journal of Fisheries Management 10:72– 

79. 

Woodward, D. K. 1977. Status and ecology of the beaver (Castor canadensis carolinensis) in South Carolina with emphasis on the Piedmont. M.S. Thesis, 

Clemson University, Clemson, SC. 

Woodward, D. K., R. B. Hazel, and B. P. Gaffney. 1985. Economic and environmental impacts of beavers in North Carolina. Proceedings of the Eastern 

Wildlife Damage Control Conference 2:89–96. 

Yeager, L. E., and K. O. Hay. 1955. A contribution toward a bibliography on the 

beaver (Technical Bulletin 1). Colorado Department of Game and Fish. 

Zeckmeister, M. T., and N. F. Payne. 1998. Effects of trapping on colony density, 

structure, and reproduction of a beaver population unexploited for 19 years. 

Transactions of the Wisconsin Academy of Sciences, Arts, and Letters 

86:281–91. 

Zurowski, W., J. Kisza, A. Kruk, and A. Roskosz. 1974. Lactation and chemical 

composition of milk of the European beaver (Castor fiber L.). Journal of 

Mammalogy 55:847–50. 

B W. B, U.S. Geological Survey, Fort Collins Science Center, 

2150 Centre Avenue, Bldg. C., Fort Collins, Colorado 80526-8118. Email: 

Bruce Baker@usgs.gov. 

E P. H (retired), Mississippi Cooperative Fish and Wildlife 

Research Unit, Mississippi State University, Mississippi State, Mississippi 

39762.