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A
Bit About Beavers:
Breeding
season - Breeding occurs between January and March. Beavers
are generally monogamous, although males will mate with other females.
Only the colony's dominant female breeds, producing one litter a
year.
Gestation/litter - Gestation period lasts 4 months.
Average litter size varies between 2.3 and 4.1. Kits are weaned
at 2 to 3 months and can swim by 1 week of age.
Age at sexual maturity - Beavers become sexually mature between
age 2
and 3.
Colony/dispersal - The colony consists of three
age classes of beavers: the adults, the kits, and the yearlings
born the previous spring (average 5.1 beavers per colony). After
young beavers reach their second or third year, they are forced
to leave the family group. Dispersal may be delayed in areas with
high beaver densities. Subadults generally leave the natal colony
in the late winter or early spring. Subadult 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).
Life span - Up to 11 years in the wild, 15 to 21
years in captivity.
The species is active throughout the year and is usually nocturnal.
Adult beavers are nonmigratory.
Preferred Habitat :
Suitable habitat for 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. 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 beavers. Intermittent streams or streams
that have major fluctuations in discharge will have little year-round
value as beaver habitat.
Stream characteristics such as gradient, depth, and width are determining
factors in habitat use by beaver. Steep topography prevents the
establishment of a food transportation system. Additionally, narrow
valley bottoms cannot support the large amounts of vegetation needed
by beavers. Consequently beaver populations in narrow
valley bottoms are more cyclic than are populations in wider valley
bottoms. Valleys less than 150 feet (46 m) wide are occupied less
frequently. One study found that 68 percent of the beaver colonies
were in valleys with a stream gradient of less than 6 percent. Valleys
that were only as wide as the stream channel were unsuitable beaver
habitat, while valleys wider than the stream channel were frequently
occupied by beavers.
Food availablity is another factor determining suitable habitat
for beavers. Marshes, ponds, and lakes are often occupied by beavers
when an adequate supply of food is available. 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.
Cover Requirements :
The lodge is the major source of escape, resting, thermal, and reproductive
cover for beavers. Lodges may be surrounded by water or constructed
against a bank. Water protects the lodge from predators and provides
concealment for beavers when traveling to and from food gathering
areas and caches. On lakes and ponds, lodges are
frequently situated in areas that provide shelter from wind, waves,
and ice. Damming large streams with swift, turbulant waters creates
calm pools for feeding and resting.
Food Habits:
Beavers are herbivores. During late spring and summer their diet
consists mainly of fresh herbaceous matter. 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.
Winter is a critical period, especially for colonies on streams
because they must subsist solely on their winter food caches. In
contrast with stream 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.
Woody stems cut by beavers are usually less than 3 to 4 inches (7.6-10.1cm)
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.
Beaver activity can have a significant influence on stream and riparian
habitats. 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. Additionally,
beaver ponds conserve spring runoff, thus ensuring
more constant stream flow, diminishing floods, conserving soil,
and helping maintain the water table.
Beaver activity can be beneficial to some wildlife species. Waterfowl
often benefit from the increased edge, diversity, and invertebrate
communities created by beaver activity. Occupied beaver-influenced
sites produce more waterfowl because of improved water
stability and increased brood-rearing cover; the production declines
with beaver abandonment. Great-blue herons (Ardea herodias), ospreys
(Pandion halietus), eagles (Haleaeitus leucocephalus), kingfishers
(Ceryle alcyon), and many species of songbirds benefit from beaver
activity as well. Otters, raccoons (Procyon lotor), mink, and muskrat
(Ondatra zibithica) thrive on the increased foraging areas produced
by
beaver activity. Berry-producing shrubs and brush in areas cut over
by beavers attract white-tailed deer (Odocoileus virginianus) and
black bear (Ursus americanus).
Beaver activity can also improve fish habitat.
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