Biology Reference
In-Depth Information
ponds and raise their broods on the ponds. Cavity-nesting birds, including wood ducks and golden eyes,
find nest sites in standing dead trees killed by the flooding from beaver flowages. Herons, bitterns,
egrets, and other wading birds find fertile hunting grounds along the shallow margins of these myriad
bodies of water.
Other forms of life benefit from the beavers as well. Fish often thrive in beaver ponds, at least for a
few years after the pond's creation. Frogs, turtles, salamanders, water snakes, insects, and other aquatic
creatures occupy these new wetlands in large numbers. Indeed, a whole host of creatures benefits from
the beaver and its wetlands.
After a period of years, a beaver colony's supply of food and building materials begins to diminish.
As food becomes scarcer, the beavers resort to various strategies to stretch out the life of the colony.
Normally, beavers don't go much more than one hundred yards from their home ponds in search of
food, but with declining food supplies they may increase that distance. They will also dig canals lead-
ing away from a pond so that they can transport food and building materials to the pond by water. As a
last resort, they'll even begin to exploit normally shunned food sources, such as the bark of evergreens.
Almost inevitably, however, supplies finally run out, and the beavers depart. However, their depar-
ture doesn't by any means signal the end of the beaver's usefulness in creating habitat for other species.
Without constant attention, the dam soon deteriorates and gradually disappears, leaving a wide, muddy
expanse. Fertilized by beaver droppings, this mud flat quickly revegetates, first with grasses and other
herbaceous plants, and later with shrubs and tree seedlings.
The former pond is now called a beaver meadow—a very different type of habitat from the beaver
pond, but nonetheless a valuable one. Deer, moose, and other creatures come here to graze, browse, and
otherwise feed on this rich new food source. Gradually, though, the shrubs and trees grow large enough
to provide a food supply for beavers once again. Then beavers return, and the cycle repeats itself, as it
has for thousands of years.
Not all is well with the resurgence of the beaver, however. At first it was greeted joyfully by most
people. As they became more and more numerous, however, conflicts between beavers and their works
and humans began to mount. Now beavers, once a favorite of nearly everyone, are so numerous that
they've become pariahs in the eyes of many people. As a result, they've created discord not only
between beavers and humans, but also between beaver lovers and beaver haters. What created this re-
markable shift in the attitude of so many individuals toward the big rodents?
The beaver's reproductive potential is a good place to begin seeking answers. Once beavers are well
established, they can multiply very rapidly. They begin to breed at age two or three and can easily live
for twelve to fifteen years, and sometimes as much as twenty. Thus, even allowing for normal attrition
among their offspring, a single pair of beavers can produce a very large number of survivors in the
course of a lifetime.
Abetting this reproductive capacity is the relative lack of predation. The beaver is a large animal. It
happens to be the world's second largest rodent, topped only by the South American capybara. Adult
beavers average forty to fifty pounds, and exceptionally large specimens can reach seventy, eighty, even
