Biology Reference
In-Depth Information
ninety pounds. In fact, the largest beaver ever recorded actually exceeded one hundred pounds. (Al-
though large by present-day standards, the beaver is a midget compared with one of its ancestors: a sort
of giant beaver named
Trogonotherium
lived about a million years ago and was seven feet long!)
Any animal that weighs fifty pounds or more, and is armed with a set of powerful chisel teeth, is
a formidable opponent for all but the biggest and strongest predators. Prior to the advent of European
settlers, the only major North American predators of beavers were Native Americans, wolves, and cou-
gars. Much of the predation by the latter two was probably carried out at the time when the two-year-old
beavers dispersed; traveling overland or along shallow streams much of the time, these itinerant young
beavers were highly vulnerable to large predators.
Nowadays, wolves and cougars control beavers only where enough wild country remains to support
those big predators. However, it's unreasonable and impractical to expect wolves and cougars to return
to populated areas. Bears, bobcats, and coyotes will kill an occasional young beaver, and otters prey on
baby beavers now and then, but their predation is too sporadic to have much overall effect on such a
prolific animal.
That leaves humans as the only major restraint—other than starvation and disease—on beaver pop-
ulations. For a few decades, trapping held beaver populations at a reasonable level, more or less in bal-
ance with habitat. This system began to come unglued, however, when felt hats—the best ones, man-
ufactured from the beaver's underfur—went out of style in the 1960s. Prices for beaver pelts declined
and, as a consequence, so did human predation on beavers. With reduced predation, beavers multiplied
and became an increasingly serious nuisance in many areas.
When I was a small child growing up in Vermont, my parents took me to a museum in which a Ver-
mont map displayed the location of all the state's known beaver colonies, indicated by a handful of
widely scattered red dots. Today a similar map would be almost totally red, so abundant are the state's
thousands of beaver colonies!
As more and more young beavers seek places to establish a colony, they gradually occupy every
available nook and cranny. In fact, I've seen numerous dams and ponds so tiny that they can have no
possible value to the beavers except, out of sheer desperation, to satisfy their dam-building compulsion.
This constant, widespread dam construction often brings the builders into sharp conflict with humans.
For example, beavers love to plug culverts, thereby flooding highways. The beavers don't do it to be
malicious, of course: they're acting purely from instinct. To them, a culvert simply seems like a very
narrow constriction in a stream—a perfect place to build a dam. Malicious or not, however, the road is
still flooded, and the beavers have to go.
Getting rid of beavers in this situation is not simple. Tearing a big hole in their dam (no easy feat,
incidentally, as many have discovered) is a futile gesture. Beavers are thoroughly industrious creatures,
and the sound of running water—other than that trickling through and over the very top of their dam—is
anathema to them. Consequently, they'll plug a large gap in their dam in a single night. Worse yet,
beavers are as persistent as they are hard-working, and they'll continue to repair the damage night after
night until human patience is exhausted.
