Saturday, September 1, 2007

National symbol or ugly Canadian?

This past spring a beaver took up residence in the Bronx River in New York, two centuries after that species had been eradicated from the region. This was seen as a hopeful sign that the river is returning to a cleaner, more natural state. Nature clawing its way back into ravaged places is always encouraging, and who among us would not root for the animal on our nickel, Castor canadensis? But be careful what you wish for. This creature can certainly cause headaches, with its penchant for taking hydrological control of the neighbourhood. You probably would not want to release a bunch of them into an ecosystem unprepared for their almost human knack of changing their surroundings to suit themselves.

The beaver is an aquatic animal, slow and awkward on land. It requires a watery world in which to construct a home with a submerged entrance – either a lodge made from stacked wood and mud, or a hole in a bank – which provides a place to raise young, safe from most predators. They build their famous dams across streams to raise water levels, eventually converting forests to large ponds. They are then able to swim in relative safety to the stands of trees used for food and construction. In the dead trees that remain standing, many species of insects, birds and mammals find food and places to roost.

The reason beavers disappeared from New York long ago is the same reason they are on our nickel. Their soft, dense undercoat could be converted into high quality felt hats, which were all the rage in Europe during the seventeenth and eighteenth centuries. Demand for their pelts contributed to the opening up of Canada as eastern beaver populations dwindled. Their disappearance in the east had ecological consequences. As dams disintegrated, flooded areas drained, producing rich pastureland. Aquatic species and those associated with wildlife trees declined, to be replaced by those that benefit from fertile pastureland, most notably humans.

There have been efforts to reintroduce beavers to parts of their historical range, with some success. Less wisely, beavers have been released into places no Canadian rodent has ever before set foot. In the middle of the last century, Canadian beavers were introduced into Europe. They became well-established in Finland and neighbouring Russia. At almost the same time, attempts were being made to reintroduce the European beaver, a similar species that had been extirpated for its fur centuries earlier. The success of the latter is now threatened by the spread of the former, because the Canadian beaver reproduces more quickly and colonizes new territory more readily.

In hopes of encouraging a South American fur industry, twenty-five beaver pairs from Canada were released in Tierra del Fuego in1946. They quickly spread, and now exist in Argentina and adjacent Chile in the tens of thousands. Their industriousness has flooded vast areas of native forest, causing significant environmental damage and economic hardship.

Introduced, invasive species of animal and plant are found almost everywhere, yet we tend to think primarily of immigrant examples, what is invading where we live — rats, mice, eastern grey squirrels, those pesky European starlings. Although not an ecological surprise, it comes as a bit of a cultural shock that one of our national symbols has risen (or sunk) to pest status in other places. Ex-patriot beavers have become ugly Canadians!

Coincidentally, a semi-aquatic South America rodent, known to the fur industry as the nutria, has escaped from fur-farms into North American ecosystems, including some in Washington State. The nutria resembles a large muskrat, and can be a problematic burrower in banks and dykes, but in work ethic and adaptability has yet to match Castor canadensis. That our rodent packs a bigger punch is something we can take some pride in, I suppose. Or maybe not.

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