Owls Aren't Wise and Bats Aren't Blind (4 page)

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 leading 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 departure 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 remarkable 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 ninety pounds. In fact, the largest beaver ever recorded actually exceeded one hundred pounds. (Although 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 cougars. 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 populations. For a few decades, trapping held beaver populations at a reasonable level, more or less in balance with habitat. This system began to come unglued, however, when felt hats—the best ones, manufactured 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 Vermont 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.

Dynamite may then become the weapon of choice, but even blowing a beaver dam to hell and gone won’t work unless it’s done so late in the year that the beavers have no chance to rebuild before winter. Otherwise the dam is back in a trice, the beavers are again in business, and flooding remains a problem. If the dam is totally destroyed late in the year, however, the beavers are doomed to starve or fall to predators as soon as winter arrives.

So-called “beaver cheaters”—long, perforated pipes or wood-and-screen structures inserted through the dam—sometimes work. With their upstream ends near the bottom of the pond and far enough above the dam, these devices are sometimes able to confuse the beavers and prevent them from discovering the source of the leakage. At other times, though, the dam builders, with their uncanny ability to detect current, will locate and plug the offending structures.

Another serious problem is that beavers fail to distinguish between fruit and shade trees and wild trees. Homeowners are understandably upset when this happens, yet the beavers are often forced to utilize every inch of available habitat—including cultivated trees and shrubs. This, of course, is small solace to the person whose prize fruit trees or treasured shade trees suddenly resemble the aftermath of George Washington’s mythical “Father, I cannot tell a lie” episode.

A neighbor of mine described just such an incident. Several years ago he lived on the edge of a large, marshy area. Beavers soon appropriated this spot and built a dam and lodge. There were several homes bordering this new beaver pond, and for a time everyone was delighted by the new residents. Then the problems began.

Each year the beavers raised the dam and the water level a bit, and after four or five years the water began creeping into septic-system leach fields. Moreover, the beavers began to run out of food and sought whatever they could find around their pond. What they could find happened to include the fruit trees in this man’s backyard. Formerly very pro-beaver, his opinion, he admitted, underwent a rapid and dramatic shift at that point. “I like beavers,” he commented dryly, “but I think I like apple trees more.”

Unsuccessful efforts were made either to evict the beavers by peaceable means, or to lower the level of their impoundment. The dam was torn out repeatedly, and was promptly restored by the beavers on each occasion. Then supposedly beaverproof outlet structures were installed, but the clever and industrious rodents managed to plug them all.

Finally an adjoining homeowner, whose septic system was seriously impaired by the beaver flowage, obtained a permit from the state to kill the beavers. This caused a neighborhood squabble, with some opposed to killing the beavers (mainly those who hadn’t suffered beaver damage), and others in favor of their summary execution (mainly those who
had
suffered damage).

In the midst of this turmoil, the beavers themselves solved the problem. Constantly seeking new sources of food and building supplies, they began to cross a busy paved highway adjoining their pond. Beavers weren’t designed by nature for crossing highways safely, and humans in automobiles soon became predators, albeit unintentionally, of these particular specimens.

Similar damage recently made headlines when beavers gnawed down some of the famous Washington, D.C., cherry trees near the Jefferson Memorial. The beavers had taken up residence in the Tidal Basin between the Jefferson Memorial and the Washington Monument, and in characteristic beaver fashion began to search for materials for dam and lodge, as well as food. Park Service officials managed to live-trap them and move them to another location, thereby at least temporarily forestalling further damage to the cherry trees. How well the beavers will survive in another location is highly problematic.

Timber companies and small timberland owners also suffer substantial damage when valuable trees are inundated by beaver flowages and soon die. Annual losses of timber to beaver damage may even run as high as hundreds of millions of dollars nationally.

The first response of the property owner who’s suffering damage is to ask the state wildlife agency to fix the problem. This puts the agency in a difficult position, because the owner usually balks when told that the offending animals must be killed. Instead, the complainant wants the beavers caught in a box trap and relocated. While this may seem kind, it’s actually quite the opposite.

In order to understand this seeming contradiction, another facet of beaver biology must be explored. Far from being the peaceful creatures which they appear to be, beavers are highly territorial. If a strange beaver comes to their colony, the inhabitants will either kill it or drive it away. Fierce territorial battles abound where beavers are plentiful, and older beavers soon become heavily battle-scarred from their confrontations with interlopers.

Consider, then, the plight of beavers removed from their colony and set adrift. If the distance is short enough, they will simply return to their former home, thereby continuing the original problem. Otherwise they must either try to enter another beaver colony—a recipe for certain disaster—or try to establish another colony. With virtually every available bit of beaver habitat already taken, the chances that they will succeed are infinitesimal. Further, unless they are transported in the spring, there’s insufficient time for them to build a dam and lodge and store food before the onset of winter. In summary, a beaver taken from its colony and left somewhere else has been handed an almost certain death sentence from starvation, from the onset of winter, or, in its weakened condition, at the fangs of predators.

Although the trap-and-transport option may keep the property owner from feeling guilty that he or she has been directly responsible for a beaver’s death, it would have been far kinder to simply shoot the beaver in the first place. That’s a major reason why most state wildlife agencies now refuse to trap and transport live beavers, even though this stance angers some people. These professionals realize that it’s far less cruel to kill the beavers outright than to doom them to a slow, painful death.

In a few well-publicized instances, animal rights activists have tried to save beavers by having them live-trapped, neutered by veterinarians, and returned to their former haunts. This, it turns out, is no kindness either, for it runs afoul of yet another aspect of beaver biology. Beavers, as it happens, have a social structure that’s very gender-specific; neutering creates chaos in this complex system and renders the colony ineffective for the task of survival.

Despite these conflicts with humans, the beaver is clearly here to stay. On the whole, this is a very good thing. True, some beavers will have to be removed when they cause excessive damage to the works of people, but the beaver’s insatiable appetite for building dams and cutting trees provides a wealth of prime habitat for many other wildlife species. Welcome back, beaver!

2

The Misnamed One: The Muskrat

MYTHS

The muskrat is a close relative of the common, or Norway, rat.

It’s a scaled-down version of the beaver.

It’s called a muskrat because it’s a kind of rat with a musky scent.

OUTSIDE ITS NORMAL AQUATIC SURROUNDINGS, THE MUSKRAT
(ONDATRA
ZIBETHICA) IS OFTEN MISIDENTIFIED AS A RAT, THAT IS, EITHER THE NORWAY OR COMMON RAT
(RATTUS NORVEGICUS)
OR THE BLACK OR ROOF RAT
(RATTUS RATTUS).
On several occasions I’ve had someone tell me, with either a shudder or with loathing in the voice, “A great, fat rat crossed the road in front of me. It was
huge,
just disgusting!” Or “I looked out my window, and there was the biggest rat I’ve ever seen coming up out of the water. It was awful!” After a few inquiries about specifics of the animal in question—size, shape, color, and related characteristics—it became clear that the creature being discussed wasn’t the hated and feared Norway rat, but the very distantly related and wholly innocuous muskrat.

Rats have earned their reputation as one of mankind’s greatest scourges— destructive disease carriers that have afflicted humans down through the centuries. After all, they were the primary carriers of bubonic plague—the fearsome Black Death of the Middle Ages that decimated Europe—as well as a major source of typhus. Further, their destruction of grain supplies and damage to many other things of value to humans have made them even more feared and despised. Norway and black rats are also immigrants from Europe and represent perhaps our most unfortunate importation of nonnative wildlife.

Beaver; muskrat

The muskrat, on the other hand, is a native of North America. Far from being highly destructive and a carrier of disease, it’s of great benefit to many forms of wildlife and of considerable value to humans. This interesting midsized rodent deserves to be more widely recognized and appreciated.

Even those who recognize the muskrat and don’t confuse it with the common rat often tend to think of it as a sort of junior edition of the beaver. In fact, the muskrat is very much its own man, so to speak—related to neither Norway rat nor beaver except by virtue of belonging to the order Rodentia. This order, incidentally, comprising some three thousand species worldwide, is the largest of all mammalian orders.

Despite some similarities to beavers in such things as appearance and habitat, muskrats are far more closely related to voles, those plump little short-tailed rodents that most of us call meadow mice. It’s not stretching things much to say that the muskrat is a very large, aquatic vole, and some scientists have actually described it in that fashion.

The origin of the muskrat’s name itself is fascinating. We might reasonably deduce that it derives from a combination of the muskrat’s long, naked tail and the slightly musky odor produced by its scent glands—but we would be wrong! Rather, the name is the product of a peculiar twist of language called
folk etymology.

Etymology is the study of word derivations, and folk etymology is the modification of an unfamiliar word by incorrect usage into something with more familiar elements. Although European settlers occasionally adopted—usually in somewhat corrupted form—Native American names for creatures with which they were unfamiliar, they tried to avoid that practice wherever possible. Their avoidance took the path either of naming a North American creature for something at least vaguely similar from Europe, or of using folk etymology to transform the name into something “sensible.”

In the present instance, the name of this little marsh-dwelling rodent was originally
musquash
in the Algonquian language. That name made little sense to the colonists, who observed that this creature could give off a musky scent and had a long, naked tail a bit like that of a Norway rat. Put these two observations—musk and rat—together and they sounded quite similar to musquash, yet seemed to make perfectsense. Voilà, Monsieur Muskrat!

As already noted, the muskrat looks much like a small beaver except for its tail, which is nothing like the beaver’s except that it’s hairless. While the beaver’s tail is rounded and relatively short, very wide, and flattened top to bottom, the muskrat’s is long, quite slender, and flattened from side to side.

The muskrat is also far smaller than the beaver. An adult varies from a foot and a half to a little over two feet long from nose to tip of tail. This total length is deceptive, however, for the long tail consumes nearly 40 percent of it; as a result, adult muskrats weigh only two to four pounds.

Aside from their fondness for water, muskrats lead very different lives from beavers. For one thing, the muskrat’s habitat requirements are far less rigid than those of the beaver. Since they don’t construct dams, muskrats have no need of suitable dam sites, or for materials for constructing dams. They need very little in the way of water; anything from a huge lake or river to a drainage ditch or farm pond suits this notably unfussy rodent. In fact, muskrats frequently utilize beaver ponds for their habitat, and the two species seem to coexist quite peaceably.

Muskrats also eat a much wider variety of foods than beavers. Whereas beavers are exclusively vegetarian, muskrats feed extensively on freshwater mussels, frogs, crayfish, and similar aquatic creatures whenever these are available. Now and then they even manage to catch a slow or unwary fish. However, their main diet is plant material; cattails (both the shoots and tubers), water lilies, duckweed, pickerel weed, assorted other pond weeds, bulrushes, sweet flag, and a variety of reeds and sedges are prime muskrat food.

Nor is the muskrat constrained by the need for the inner bark of trees that so often forces the beaver to abandon a colony denuded of surrounding trees and brush. No doubt the muskrat’s great adaptability in matters of food and habitat accounts for its nearly ubiquitous presence throughout most of North America, from the subarctic to the Gulf of Mexico.

Often the presence of beavers can be detected by gnawed pieces of wood that have floated far downstream from a colony. The first signs of the muskrat’s presence are likely to be a bit more subtle. These frequently take the form of cut pieces of cattails and other aquatic plants, floating about or lodged on the shoreline, and these are easily overlooked except by the careful observer. Far more obvious is the sight of some aquatic greenery mysteriously moving across the surface of the water. In the latter case, closer inspection reveals that it’s a sort of wildlife version of Birnam Wood coming to high Dunsinane—a muskrat, almost totally submerged, propelling a bunch of cut vegetation to a preferred feeding site.

These favorite feeding spots vary widely. They may be flat rocks, logs, stumps, matted vegetation, or a composite of trampled mud and reeds. Often a heap of discarded mussel shells or the remains of a number of crayfish announce the location as a choice dining spot for the resident muskrat.

Not only are muskrats more flexible than beavers in regard to food and habitat, but they’re also less choosy about living quarters. A beaver is compulsive about building a lodge, and digs a tunnel into a bank only as a last resort in situations where constructing a dam or lodge is totally impractical. Even in a large body of water with an outlet that beavers can’t possibly dam, the big rodents will fabricate a lodge near shore, provided the shoreline doesn’t drop off too abruptly or isn’t excessively rocky. A muskrat, on the other hand, usually lives in a burrow by preference, but is perfectly at ease building a house in marshes where there are no convenient banks steep enough for burrowing.

A muskrat burrow can be quite long—up to fifteen feet—angling up and back from just below the surface of the water. With a larger living chamber at the end, and several escape tunnels, the whole affair can be fairly elaborate. Although muskrats are generally very beneficial, their tunneling proclivities sometimes cause damage to dikes and small earthen dams, making them unwelcome residents in some situations.

A muskrat house is much less strong and elaborate than a beaver lodge. These little domed structures are made in autumn by heaping up a mixture of reeds and mud. The muskrat then burrows up into the mass from below the waterline, excavates a chamber, and digs out additional tunnels for escape routes beneath the water.

Next the muskrat erects several smaller, ancillary structures within a few yards of the main lodge. These little affairs, called
pushups,
enable the muskrat to extend its feeding range when the marsh or pond is icebound. In late fall or winter, after the marsh vegetation has died down, these houses and pushups can be seen dotting large marshes, protruding above the water or ice.

Muskrats even manage to find housing in large swamps that lack banks for burrowing and cattails or similar vegetation for constructing houses. In that event, a muskrat will utilize a hollow log or stump, proving once again how adaptable a creature it is.

Muskrats are an extremely important component of many wetlands. Where they’re abundant, they consume an enormous amount of aquatic vegetation, particularly emergent species such as cattails. Without these industrious little harvesters, many wetlands would have almost no open areas, because cattails and similar plants would soon choke out most of the open spaces. Indeed, the percentage of open water in a marsh is often highly dependent on the muskrat population.

This propensity for creating openings in wetlands makes the muskrat extremely valuable to other species. Without open areas, ducks, geese, herons, egrets, and numerous other birds would derive little benefit from marshes, shallow ponds, and similar wet areas. Moreover, areas of open water create places for a variety of submerged aquatic plants to grow, thereby contributing greatly to the wetland’s diversity.

Unlike beavers, muskrats seem to have little territorial instinct except in connection with their actual homes. This trait makes excellent evolutionary sense when one thinks about it: if muskrats were as fiercely territorial as beavers, they would be in constant conflict, and it would be very difficult for large numbers of them to coexist in the same marsh.