American Beaver

American beavers commonly inhabit riparian areas of mixed coniferous-deciduous
forests and deciduous forests containing abundant American beaver foods and lodge
building material such as quaking aspen (Populus tremuloides), willows
(Salix spp.), alders (Alnus spp.), red-osier dogwood (Cornus sericea),
and cottonwoods (Populus spp.) [2,25].

American beaver
Canadian beaver
beaver
flat-tail
bank beaver
castor
castor cat

More info for the term: cover

The lodge is the major source of escape, resting, thermal, and
reproductive cover for American beavers. Lodges may be surrounded by water or
constructed against a bank. Water protects the lodge from predators and
provides concealment for American beavers when traveling to and from food
gathering areas and caches [2]. On lakes and ponds, lodges are
frequently situated in areas that provide shelter from wind, waves, and
ice [2]. Damming large streams with swift, turbulent waters creates
calm pools for feeding and resting [11].

More info for the term: tundra

The American beaver is found throughout most of North America except in the
Arctic tundra, peninsular Florida, and the Southwestern deserts
[2,31,35]. The distribution of six subspecies is listed below [10,19].
The distribution of the other seven was not found in the literature.

C. c. subsp. carolinensis - occurs in the southeastern part of the United
States north to southern Virginia, northern Ohio, Indiana, Illinois, and
west to southeastern Iowa, eastern Missouri, eastern Arkansas and
Louisiana [19].

C. c. subsp. taylori - occurs in northern Nevada in the streams and
tributaries of the Snake River drainage [10].

C. c. subsp. baileyi - occurs in the Humboldt River drainage [10].

C. c. subsp. repentinus - occurs along the Colorado River [10].

C. c. subsp. texensis - occurs in eastern Texas [10].

C. c. subsp. leucodenta - occurs along the Coast Ranges from California to
Alaska [10].

More info for the terms: fresh, herbaceous, shrubs, tree

American beavers are herbivores. During late spring and summer their diet
consists mainly of fresh herbaceous matter [2,18]. American beavers appear to
prefer herbaceous vegetation over woody vegetation during all seasons if
it is available. Woody vegetation may be consumed during any season,
although its highest utilization occurs from late fall through early
spring when herbaceous vegetation is not available. The majority of the
branches and stems of woody vegetation are cached for later use during
the winter [2].

Winter is a critical period, especially for colonies on streams because
they must subsist solely on their winter food caches. In contrast with
stream American beavers, colonies on lakes are not solely dependent on their
stores of woody vegetation; they can augment their winter diet of bark
with aquatic plants [18].

Aquatic vegetation such as duck-potato (Sagittaria spp.), duckweed
(Lemma spp.), pondweed (Potamogeton spp.), and water weed (Elodea spp.)
are preferred foods when available [2]. The thick, fleshy rhizomes of
water lilies (Nymphaea spp. and Nuphar spp.) may be used as a food
source throughout the year. If present in sufficient amounts, water
lily rhizomes may provide an adequate winter food source, resulting in
little or no tree cutting or food caching of woody materials [2,18].
Other important winter foods of American beavers living on lakes include the
rhizomes of sedges and the rootstocks of mat-forming shrubs [18].

Important woody foods of American beavers include quaking aspen, willow,
cottonwood, alder, red maple (Acer rubrum), serviceberry (Amelanchier
spp.), mountain maple (Acer glabrum), red-osier dogwood, and green ash
(Fraxinus pennsylvanica) [2,18,22]. Other woody species occasionally
utilized for food include sugar maple (Acer saccharum), black ash
(Fraxinus nigra), yellow birch (Betula alleghaniensis), hazels (Corylus
spp.), hemlocks (Tsuga spp.), and Oregon crab apple (Malus fusca)
[18,21]. Aspen and willows are considered preferred American beaver foods;
however, these are generally riparian tree species and may be more
available for American beaver foraging but not necessarily preferred over all
other deciduous tree species. American beavers have been reported to subsist in
some areas by feeding on conifer trees; however, these trees are a poor
quality source of food [2].

Woody stems cut by American beavers are usually less than 3 to 4 inches (7.6-10.1
cm) in d.b.h. One study reported that trees of all size classes were
felled close to the water's edge, while only smaller diameter trees were
felled farther from the shore. Trees and shrubs closest to the water's
edge are generally utilized first [2].

More info for the terms: climax, forest, succession

Fire occurring in riparian areas often benefits American beaver populations [16].
American beavers are adapted to the early stages of forest succession. Quaking
aspen, willows, alders, and red-osier dogwood, prime American beaver food trees,
all sprout vigorously after fire. As succession progresses, these trees
become too large for American beavers to use or are replaced by climax trees
[34]. Recurring fires within parts of boreal forests have allowed aspen
and willow to replace coniferous forests. This change favors American beaver
populations, since both species are important food sources. Fire may
also help create more open bodies of water [16].

More info on this topic.

This species is known to occur in association with the following cover types (as classified by the Society of American Foresters):

16 Aspen
18 Paper birch
19 Gray birch - red maple
20 White pine - northern red oak - red maple
22 White pine - hemlock
24 Hemlock - yellow birch
25 Sugar maple - beech - yellow birch
26 Sugar maple - basswood
27 Sugar maple
28 Black cherry - maple
30 Red spruce - yellow birch
31 Red spruce - sugar maple - beech
35 Paper birch - red spruce - balsam fir
39 Black ash - American elm - red maple
57 Yellow-poplar
58 Yellow-poplar - eastern hemlock
59 Yellow-poplar - white oak - northern red oak
60 Beech - sugar maple
61 River birch - sycamore
62 Silver maple - American elm
63 Cottonwood
88 Willow oak - water oak - diamondleaf oak
93 Sugarberry - American elm - green ash
95 Black willow
96 Overcup oak - water hickory
108 Red maple
202 White spruce - paper birch
203 Balsam poplar
210 Interior Douglas-fir
212 Western larch
213 Grand fir
217 Aspen
221 Red alder
222 Black cottonwood - willow
229 Pacific Douglas-fir
230 Douglas-fir - western hemlock
235 Cottonwood - willow
243 Sierra Nevada mixed conifer
244 Pacific ponderosa pine - Douglas-fir
245 Pacific ponderosa pine
251 White spruce - aspen
252 Paper birch
254 Black spruce - paper birch

More info on this topic.

This species is known to occur in the following ecosystem types (as named by the U.S. Forest Service in their Forest and Range Ecosystem [FRES] Type classification):

FRES11 Spruce-fir
FRES12 Longleaf-slash pine
FRES13 Loblolly-shortleaf pine
FRES14 Oak-pine
FRES15 Oak-hickory
FRES16 Oak-gum-cypress
FRES17 Elm-ash-cottonwood
FRES18 Maple-beech-birch
FRES19 Aspen-birch
FRES20 Douglas-fir
FRES21 Ponderosa pine
FRES22 Western white pine
FRES23 Fir-spruce
FRES25 Larch
FRES28 Western hardwoods

More info on this topic.

This species is known to occur in association with the following plant community types (as classified by Küchler 1964):

More info for the terms: bog, forest

K005 Mixed conifer forest
K011 Western ponderosa forest
K014 Grand fir - Douglas-fir forest
K016 Eastern ponderosa forest
K017 Black Hills pine forest
K018 Pine - Douglas-fir forest
K020 Spruce - fir - Douglas-fir forest
K021 Southwestern spruce - fir forest
K025 Alder - ash forest
K029 California mixed evergreen forest
K093 Great Lakes spruce - fir forest
K094 Conifer bog
K095 Great Lakes pine forest
K096 Northeastern spruce - fir forest
K098 Northern floodplain forest
K099 Maple - basswood forest
K100 Oak - hickory forest
K101 Elm - ash forest
K102 Beech - maple forest
K103 Mixed mesophytic forest
K106 Northern hardwoods
K107 Northern hardwoods - fir forest
K109 Transition between K104 and K106
K110 Northeastern oak - pine forest
K111 Oak - hickory - pine forest
K112 Southern mixed forest
K113 Southern floodplain forest

More info for the terms: cover, density, forest, natural, shrubs, succession, tree

American beavers will live in close proximity to humans if all habitat
requirements are met [27]. However, railways, roads, and land clearing
adjacent to waterways may affect American beaver habitat suitability. Transplants
of American beaver may be successful on strip mined land or in new impoundments
where water conditions are relatively stable. Highly acidic waters,
which often occur in strip-mined areas, are acceptable for American beaver if
suitable foods are present [2].

American beaver activity can have a significant influence on stream and riparian
habitats [3,14,24,30]. American beavers are the only mammals in North America
other than humans that can fell mature trees; therefore, their ability
to decrease forest biomass is much greater than that of other herbivores
[2]. Additionally, American beaver ponds conserve spring runoff, thus ensuring
more constant stream flow, diminishing floods, conserving soil, and
helping maintain the water table [12].

Through tree harvesting activity, American beavers can have an effect on natural
succession. According to Barnes and Dibble [3] tree cutting by American beavers
on the lower Chippewa River in west-central Wisconsin will alter the
course of succession on the riverbottom site studied. American beavers were
selective in their choice of woody plants, preferring ash (Fraxinus
spp.) and hickory (Carya spp.) over all other woody plants. These
authors predict a major reduction in density for future populations of
ash, hickory, and hackberry (Celtis spp.) in areas of American beaver activity
and an increase in the density of basswood (Tilia spp.) and elm (Ulmus
spp.) [3].

American beaver activity can be beneficial to some wildlife species [13,30].
Waterfowl often benefit from the increased edge, diversity, and
invertebrate communities created by American beaver activity [30]. Occupied
American beaver-influenced sites produce more waterfowl because of improved water
stability and increased brood-rearing cover; the production declines
with American beaver abandonment. Great-blue herons (Ardea herodias), ospreys
(Pandion halietus), bald eagles (Haliaeetus leucocephalus), kingfishers
(Ceryle alcyon), and many species of songbirds benefit from American beaver
activity as well. Otters, raccoons (Procyon lotor), mink, and muskrat
(Ondatra zibithica) thrive on the increased foraging areas produced by
American beaver activity. Berry-producing shrubs and brush in areas cut over by
American beavers attract white-tailed deer (Odocoileus virginianus) and black
bear (Ursus americanus) [30].

American beaver activity can also improve fish habitat. Production of three
trout species (Salomo spp. and Salvelines fontinalis) in a stream in the
Sierra Nevada increased due to a higher standing crop of invertebrates
in American beaver ponds [8]. Smallmouth bass (Micropterus dolomieuis) and
northern pike (Esok lucius) also benefit from American beaver impoundments [30].
In some instances American beaver ponds have provided up to six times the total
weight of salmonids per acre than that in adjacent stream habitat
without American beaver ponds [24]. In areas of marginal trout habitat, however,
American beaver activity can reduce trout production. American beaver-caused loss of
streamside shade and diminished water velocity can result in lethal
water temperatures [30].

The amount of influence that cattle have on riparian environment can be
reduced by American beaver activity in many valley bottoms. If American beavers are
thoroughly established in wide valley willow habitats prior to the
introduction of cattle, the immediate effect of cattle on the stream is
often minor [24].

American beaver activity can also have detrimental effects. American beaver-caused
flooding often kills valuable lowland timber [30]. Human/American beaver
conflicts occur when American beavers flood roadways and agricultural lands, and
dam culverts and irrigation systems. The economic cost of nuisance
American beaver activities often exceeds the value of their pelts and has been
estimated at $75 to $100 million annually in the United States.
Additionally, American beavers have potential to increase water-borne pathogens
(including Giardia lamblia) downstream from their activity [30].

American beavers are harvested for their pelts. In most states with substantial
American beaver populations, the species is now managed to provide a reliable
annual harvest and a relatively stable population [12].

AL
AK
AZ
AR
CA
CO
CT
DE
FL
GA

ID
IL
IN
IA
KS
KY
LA
ME
MD

MA
MI
MN
MS
MO
MT
NE
NV
NH
NJ

NM
NY
NC
ND
OH
OK
OR
PA
RI
SC

SD
TN
TX
UT
VT
VA
WA
WV
WI
WY

DC
PR
VI

AB
BC
MB
NB
NF
NT
NS
ON
PE
PQ

SK
YT


MEXICO

More info for the term: natural

American beavers have few natural predators. However, in certain areas, American beavers
may face predation pressure from wolves (Canis lupus), coyotes (Canis
latrans), lynx (Lynx canadensis), fishers (Martes pennanti), wolverines (Gulo
gulo), and occasionally bears (Ursus spp.). Alligators, minks (Mustela
vison), otters (Lutra canadensis), hawks, and owls periodically prey on
kits [19,22,27]. Humans kill American beavers for their fur [18,22].

Suitable habitat for American beavers must contain all of the following: stable
aquatic habitat providing adequate water; channel gradient of less than
15 percent; and quality food species present in sufficient quantity [2].
American beavers can usually control water depth and stability on small streams,
ponds, and lakes. Large lakes or reservoirs (20 acres [8 ha] in surface
area) with irregular shorelines provide optimum habitat for the species.
Lakes and reservoirs that have extreme annual or seasonal fluctuations
in the water level are generally unsuitable habitat for American beavers [2,28].
Intermittent streams or streams that have major fluctuations in
discharge will have little year-round value as American beaver habitat [2].

Stream characteristics such as gradient, depth, and width are
determining factors in habitat use by American beaver [2,11]. Steep topography
prevents the establishment of a food transportation system [2].
Additionally, narrow valley bottoms cannot support the large amounts of
vegetation needed by American beavers. Consequently American beaver populations in narrow
valley bottoms are more cyclic than are populations in wider valley
bottoms [24]. Valleys less than 150 feet (46 m) wide are occupied less
frequently [2,24]. One study found that 68 percent of the American beaver
colonies recorded in Colorado were in valleys with a stream gradient of
less than 6 percent. No American beaver colonies were recorded in streams with a
gradient of 15 percent or more. Valleys that were only as wide as the
stream channel were unsuitable American beaver habitat, while valleys wider than
the stream channel were frequently occupied by American beavers [24].

Food availability is another factor determining suitable habitat for
American beavers [11]. Marshes, ponds, and lakes are often occupied by American beavers
when an adequate supply of food is available. American beavers generally forage
no more than about 300 feet (90 m) from water; however, foraging
distances of up to 656 feet (200 m) have been reported [2].

More info on this topic.

This species can be found in the following regions of the western United States (according to the Bureau of Land Management classification of Physiographic Regions of the western United States):

1 Northern Pacific Border
2 Cascade Mountains
3 Southern Pacific Border
4 Sierra Mountains
5 Columbia Plateau
6 Upper Basin and Range
7 Lower Basin and Range
8 Northern Rocky Mountains
9 Middle Rocky Mountains
10 Wyoming Basin
11 Southern Rocky Mountains
12 Colorado Plateau
13 Rocky Mountain Piedmont
14 Great Plains
15 Black Hills Uplift
16 Upper Missouri Basin and Broken Lands

The currently accepted scientific name for the American beaver is Castor
canadensis Kuhl [6,10,19,22,33]. The subspecies differ in size,
proportion, color, and skull characteristics [10,33]. The following
subspecies have been mentioned in the literature [10,19,22,29,33]:

C. canadensis subsp. baileyi Nelson
C. canadensis subsp. belugae Taylor (Cook Inlet beaver)
C. canadensis subsp. canadensis Kuhl (Canadian beaver)
C. canadensis subsp. carolinensis Rhoads (Carolina beaver)
C. canadensis subsp. frondator Mearns (Sonora beaver)
C. canadensis subsp. leucodonta Gray (Pacific beaver)
C. canadensis subsp. mexicanus Bailey (Rio Grande beaver)
C. canadensis subsp. michiganensis Bailey (woods beaver)
C. canadensis subsp. pacificus Rhoads (Washington beaver)
C. canadensis subsp. phaeus Heller ( Admiralty beaver)
C. canadensis subsp. repentinus Goldman
C. canadensis subsp. taylori Davis
C. canadensis subsp. texensis Bailey (Texas beaver)

More info for the term: litter

Breeding season - Breeding occurs between January and March
[18,30,31,35]. American beavers are generally monogamous, although males will
mate with other females [22,31]. Only the colony's dominant female
breeds, producing one litter a year [30].

Gestation/litter - Gestation period lasts 4 months. Average litter size
varies between 2.3 and 4.1 [27,30,31,35]. Kits are weaned at 2 to 3
months and can swim by 1 week of age [31,35].

Age at sexual maturity - American beavers become sexually mature between age 2
and 3 [18,36].

Colony/dispersal - The colony consists of three age classes of American beavers:
the adults, the kits, and the yearlings born the previous spring
(average 5.1 American beavers per colony) [18]. After young American beavers reach their
second or third year, they are forced to leave the family group
[18,22,35]. Dispersal may be delayed in areas with high American beaver
densities. Subadults generally leave the natal colony in the late
winter or early spring [30]. Subadult American beavers have been reported to
migrate as far as 147 miles (236 km), although average migration
distances range from 5 to 10 miles (8-16 km) [2].

Life span - Up to 11 years in the wild, 15 to 21 years in
captivity [22,27].

The species is active throughout the year and is usually nocturnal.
Adult American beavers are nonmigratory [2].

More info for the terms: fire regime, forest

Fire can be used to maintain American beaver habitat in a subclimax state, thus
ensuring adequate food supply for American beavers [16,26,34]. High American beaver
populations in many areas are the direct result of the extensive
clearcutting and forest fires which were characteristic of the northern
forests until recent years [25,34].

FIRE REGIMES :
Find fire regime information for the plant communities in which this
species may occur by entering the species name in the FEIS home page under
"Find FIRE REGIMES".