|The Mammals of Texas -
Rodentia : Family Castoridae : Castor
Description. A large, robust, aquatic
rodent with a broad, horizontally flattened, scaly tail;
hind feet webbed; upperparts in fresh fall pelage dark,
rich, chestnut brown which fades by spring; underparts
paler, often with silvery sheen. Sexes colored alike.
External measurements average: total length, 1,160 mm;
tail, 400 mm; hind foot, 178 mm. Weight, averages 18 kg;
rarely as much as 27 kg. The dental formula is I 1/1, C
0/0, Pm 1/1, M 3/3 X 2 = 20.
Distribution in Texas. Found over most of
the state where suitable aquatic habitat prevails; absent
from the Llano Estacado and some adjacent areas and from
much of the Trans-Pecos.
Habits. Beavers are essentially
aquatic and require water in the form of a pond, stream,
lake, or river for their well-being. Because of their
skills in regulating water level and stream flow with
dams, beavers are able to convert an otherwise
unfavorable area into one that is habitable. But they
must be ever alert as water engineers because their ponds
tend to fill up with sediment washed off the slopes above
and in time become meadows, forcing the beavers to move
to new sites. Large rivers and lakes offer suitable
habitat in places where natural food and den or house
sites are available, but the largest populations are on
small bodies of water.
In cold regions, beavers live in houses
constructed of sticks and mud and enter and leave them by
means of underwater tunnels or "plunge holes";
in Texas they may burrow into cut banks of streams or
lakes. Burrows examined in the Rio Grande in the Big Bend
section of Texas were large enough to admit a man and
were 10 m or more in length. Burrows as long as 50 m have
been reported. Burrows, or houses, are used for loafing,
sleeping, and rearing the young.
The average beaver colony consists of
six or seven animals, usually including parents and their
young of two age classes; rarely is it as large as 12.
Beavers feed on a variety of
vegetation, but the inner bark of willows and cottonwood
seems to be their mainstay. In summer a number of
herbaceous aquatic plants and sedges are eaten. In
central Texas, where willows are absent, beavers in
winter utilize as first choice such trees as button
willow, juniper, and pecan and rely heavily on Bermuda
grass, beard grass, ragweed, and yellow water lily in
summer. Thus, the plants eaten and their order of
preference depend in large measure on availability.
Breeding begins in January or February,
and the young are normally born in May or June after a
gestation period of about 107 days. Beavers are usually
monogamous, and normally only one litter of three to four
young is produced each year, but some females produce a
second litter in August or September.
At birth the kits are fully furred, the
eyes are open, and the incisor teeth are visible; they
weigh about 450 g. The tail is broad and flat, as in
adults. They grow rather slowly and attain a weight of
about 10 kg the first year. They mature sexually the
second year. Rarely, yearling females may breed and
produce young. The young often stay with the family group
through the second year.
Because of the high commercial value of
their pelts, beavers figured importantly in the early
exploration and settlement of western North America.
Thousands of their pelts were harvested annually, and it
was not many years before beavers were either
exterminated entirely or reduced to very low populations
over a considerable part of their former range. By 1910
their populations were so low everywhere in the United
States that strict regulation of the harvest or complete
protection became imperative. In the 1930s live trapping
and restocking of depleted areas became a widespread
practice which, when coupled with adequate protection,
has made it possible for the animals to make a
spectacular comeback in many sections. Their value as
soil and water conservationists is well-known and, in
most sections of the country, appreciated. They can be
destructive to crops, trees, and irrigation systems,
however, in which case they can be live-trapped and
removed from the area.
Photo credit: John L. Tveten.