Owls Aren't Wise and Bats Aren't Blind (25 page)

About twenty-five years ago, there was a great furor over the Vermont Fish and Wildlife Department’s deer management policies. Some of the more vitriolic critics resorted to making anonymous (and completely false) allegations of moral turpitude and legal misdeeds against prominent department employees. As a result, I was eventually asked to chair a committee to investigate these charges.

In addition to deer management policies, the department was also being criticized for not trying to extirpate the recently reintroduced fisher. When our committee sought reasons for this, a prominent critic—who was decent enough not to hide behind anonymity—sent us a copy of a
National
Geographic
publication that contained the striking assertion (as nearly as I can recall it), “Its green eyes glowing with hatred, the fisher attacks anything unfortunate enough to cross its path.”

When we asked
National Geographic,
normally distinguished for its impeccable science, for the source of this astonishing description, they cited Ernest Thompson Seton. Alas for scientific accuracy, Seton, in many ways a remarkably accurate observer of wildlife, all too often lapsed into flights of anthropomorphism and melodrama. This instance is a prime example! All predators are fierce when it comes to killing their prey; they couldn’t survive otherwise. The fisher is no more ferocious than most other predators, however, and indeed seems to be rather less fierce than many in its attitude toward humans.

Henry Laramie, a biologist with the New Hampshire Fish and Game Department for many years, asserts that fishers are very docile as far as humans are concerned. He once handled twenty-five fishers that were still in live traps; to prove this very point, he touched each fisher on the nose with his index finger as soon as he arrived at a trap. Not a single fisher bit him! On other occasions, Laramie had wild fishers loose in his car, running across his lap and shoulders; again, he suffered no bites. So much for the notion that fishers are incredibly ferocious!

The reproductive habits of the fisher, including delayed implantation, are quite similar to those of weasels (see below). The peak of their breeding season is in March, only about a week after the females give birth to a litter that averages three kits. The fertilized eggs remain free in the uterus for nearly eleven months; then they implant and begin to grow only about thirty-five days before the birth of the young.

The kits are born in a small cavity in a tree, usually about twenty feet above the ground. They are poorly developed at birth and don’t even open their eyes for at least fifty days. From that point on, however, they mature rapidly and are able to be on their own by the onset of winter.

In summary, it can be said that the fisher has evolved as a medium-sized predator, primarily terrestrial but with substantial arboreal capabilities. Though frequently and unjustly maligned, it’s an important part of the forest ecosystem within its range. This is especially true in regard to controlling porcupines. Further, the fisher is an extremely valuable furbearer. It deserves, and is generally receiving, management that assures its survival.

WEASELS

Weasels have long had an unsavory reputation. We speak of a person as weaseling out of an agreement, or having a weasel face. There is also an underlying, though often unspoken, assumption that weasels are horrid, nasty little beasts, evil, cruel, and bloodthirsty.

In some ways this reputation is hard to account for. Viewed dispassionately, weasels, fierce little predators though they may be, present quite a different aspect: with their bright, beady eyes, alert and inquisitive faces, lithe movements, and relative fearlessness around humans, weasels can easily be seen as cute little creatures that are fun to watch.

More than likely, it was the weasel’s occasional depredations on flocks of chickens and other domestic fowl, in a simpler time when most people lived on the land and raised their own chickens and ducks, that aroused much of this ire. And although one can understand the wrath of a farmer who found his flock of hens dead, the damage done to poultry by weasels was always minor compared to the good they did—and continue to do—in controlling mice, rats, and other rodents.

The notion that weasels are evil, cold-blooded creatures that kill for the sheer joy of killing stems from ignorance of their requirements for survival, fortified by a substantial dollop of anthropomorphism. Life is precarious for any wild creature, predator and prey alike, but especially for the weasel in winter. Consider some of the impediments to weasel survival during this harsh season.

First, the long, slender head and body, which enable a weasel to go most places where a mouse can go, are also very inefficient at preserving body heat; this problem is exacerbated by a thin fur coat and very little body fat. Second, the weasel is hyperactive, with a heartbeat in the hundreds of times a minute, so it takes a great deal of fuel to stoke its tiny furnace. Meanwhile, the pool of available prey steadily shrinks because young are rarely born during the winter months, while disease and predation take a constant toll.

Together, these ingredients form a recipe for weasel disaster—and in fact winter starvation is probably the major cause of weasel mortality. Against this formidable array of problems, evolution has programmed weasels with an effective survival strategy. This is known to biologists as “surplus killing,” the trait that has given the weasel such a sinister reputation.

Because weasels live on the ragged edge of starvation, especially in winter, they kill as much prey as they can find; any surplus is cached and enables the weasel to endure at least a short period of unsuccessful hunting. Naturalists, incidentally, noted this caching behavior at least a hundred years ago.

Thus a weasel that slaughters a flock of hens in the coop is simply obeying an instinct. Its actions have nothing to do with taking pleasure in killing and everything to do with evolutionary programming that has enabled the species to survive.

Weasels customarily kill by a bite at the base of the skull, or close by in the neck. No doubt this fact, coupled with their penchant for surplus killing, led to the idea that weasels suck the blood of their victims, like minuscule vampires sprung to life out of some horror movie. A farmer finding his coop filled with dead chickens, uneaten but with tiny puncture marks in the neck, could be forgiven for assuming that the weasel was simply dining on blood.

Weasels have also been accused, from time to time, of sucking the contents out of eggs. In
As You Like It,
Shakespeare penned the words, “I can suck melancholy out of a song as a weasel sucks eggs.” Unfortunately, the Bard was far off base with this analogy.

There are three species of weasels native to North America. In order of size, they are the long-tailed weasel
(Mustela frenata),
short-tailed weasel or ermine
(Mustela erminea),
and least weasel
(Mustela rixosa).

The long-tailed weasel is found throughout most of the continental United States, except for Alaska, as well as a little of southern Canada. The short-tail’s range is more northerly, encompassing even far northern Canada. It overlaps the long-tail’s range in southern Canada, throughout New England, New York, and Pennsylvania, in the Great Lakes region, and in much of the area from the Rocky Mountains westward. The least weasel’s range takes in Alaska and most of Canada except its far northern reaches, avoids New England and New York, then extends down the Appalachians and across the northern half of the United States to roughly the Rocky Mountains.

The long-tailed and short-tailed weasels are quite similar in appearance and habits, and they can be very difficult to tell apart except on close inspection, especially in their white winter phase. In their summer brown, however, short-tails can be distinguished by their white feet, which are lacking in the long-tails.

Long-tails are generally larger than short-tails (up to seventeen or eighteen inches long, including the tail, compared to thirteen inches for short-tails). Size, however, is not a very good criterion for quick identification; since male weasels are much larger than females, a large male short-tail can be as big as a small female long-tail. An average long-tail weighs eight ounces or less, an average short-tail less than half that.

Both species have a black tip on the tail. Except for this tip, the short-tail turns white in winter throughout most of its range. This, of course, is the famous ermine that long graced the robes of royalty. The long-tail also turns white in the more northerly parts of its range, where there is usually snow during the winter, and the white pelts with black tail tips of both species are considered ermine in the fur trade.

The white winter coat makes eminent good sense in an evolutionary scheme. Weasels are the target of numerous predators—hawks, owls, foxes, coyotes, and domestic cats among them—and the weasel’s white fur against a snowy background provides excellent camouflage.

But what of the black tip on the tail, which would seem to defeat the weasel’s camouflage? Scientists long puzzled over this seeming anomaly. Then a researcher named Roger Powell wondered if perhaps the black tip of the tail drew the attention of predators away from the weasel’s body. Using captive hawks trained to attack fake weasels “running” across a white background, he found that the hawks repeatedly attacked the black tip of the tail, rather than the “weasel’s” body. When the black tip was eliminated, the frequency of successful body attacks increased.

Although long-tailed and short-tailed weasels are very small, they are veritable giants compared to the aptly named least weasel. The smallest of the world’s true carnivores, this minuscule predator is only six and a half to eight inches long, including tail, and may weigh barely more than one ounce! It turns white in winter throughout all but the most southerly portion of its range. Curiously, however, its tail lacks a black tip; biologists believe that with a tail only one and a half inches long or less, a black tip would draw attacks too close to this tiny weasel’s body.

Starvation and predators are by no means the only dangers confronting weasels. Although they’re predominantly predators of mice, voles, and other small prey, weasels also attack larger animals such as rats and rabbits. Even the most peaceful of animals will defend itself with desperate courage and energy when cornered; hence weasels sometimes suffer fatal wounds when they attack prey many times their own size and weight. Incidentally, although weasels have excellent eyesight and hearing, they often use their keen sense of smell to track their prey.

Delayed implantation, already mentioned prominently, has some major advantages for a predator with the weasel’s habits. In order to understand these advantages, let’s start with the birth of a litter of kits, normally in April. There are usually six or seven kits, but litter size can vary widely.

The kits are blind, nearly hairless, and extremely tiny—premature by the standards of most mammals. This arrangement is vital to the mother, who must retain her slender outline and light weight in order to hunt successfully and survive throughout her entire pregnancy.

Breeding occurs three months later, in July or early August. The male comes to the den and woos the female with presents of dead mice and other prey; this allows the female to spend time breeding, rather than hunting.

Now comes the most unusual part—one that clearly demonstrates what a great advantage delayed implantation is to weasels. Not only does the male breed the mother, but her daughters as well! Because the fertilized eggs simply float around for about eight months before attaching to the uterus walls and starting to grow, the little juvenile females have time to grow to adult size before the fetuses develop within them. Since the average life span of weasels is so brief—about eighteen months—this breeding strategy ensures ample numbers of young to perpetuate the species.

By virtue of one of evolution’s quirks, the least weasel is one of only two North American mustelids that don’t utilize delayed implantation. Perhaps this is because the tiny predator breeds at various times of the year and may have more than one litter annually. Instead, the least weasel has a gestation period of thirty-five days; however, the kits develop with enormous rapidity during the final few days before birth, thus sparing the female from carrying a heavy load while hunting during most of her pregnancy.

Weasels seem to have little innate fear of humans. In fact, in their pursuit of mice they’ll occasionally enter people’s houses and remain there for some time, and they commonly search and inhabit barns, sheds, and other outbuildings.

I’ve been fortunate enough to observe this behavior on a number of occasions. In the most recent episode, I had skinned a deer in our shed a day or two before, and draped the hide over a rack. When I entered the shed, a weasel slithered off, oozing through a crack with lithe, serpentine movements. Moments later it reappeared, inspected me for a moment with curious, beady eyes, then ducked out of sight again.

Gradually becoming bolder, it soon began to gnaw at pieces of meat still attached to the deer hide, and became almost oblivious to my presence. I went back to the house, grabbed my camera, and proceeded to take a number of pictures of the weasel from a distance of no more than five feet, while it largely ignored me. This was typical of the weasels I’ve observed in our outbuildings.

We generate our own electric power by photovoltaic cells, with a backup generator. One winter evening I stepped into the generator house to start the generator, turned on the light, and was startled when a weasel, in full ermine garb, suddenly appeared. Paying little heed to me, the handsome little creature darted here and there, evidently seeking the trail of a mouse or red squirrel.

From time to time the weasel zipped out through the vents at the back of the generator house—evidently to check the wood stacked in the adjoining woodshed—then reappeared so suddenly and unexpectedly that I could only reflect on the appropriateness of the old song “Pop Goes the Weasel.” Again, I retrieved my camera and took a number of photographs at close range, while the weasel seemed undeterred either by me or by the camera’s flash.