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Coal miners used to take canaries into the shafts to warn them of gas. The birds were much more sensitive to the lethal vapors than people, so the miners kept an eye on the bird while they worked, and if the canary fell off its perch, the miners skedaddled.

This is one of the first of many recorded instances of humans using birds as environmental monitors. Birds can fly. Some think they gotta fly. They move easily from place to place. If they aren't locked up in cages, they can leave a bad place and go in search of a good place, flying 20 or 30 miles an hour safely above the traffic that might doom a red fox or a starnosed mole trying a similar migration.

Clear-cut a woodland and some of the mammals will remain simply for lack of the ability to get out quickly. But the woodland birds will be gone immediately, instantly replaced by a whole new set of species that prefer clear-cut woodlands. New mammals will invade much more slowly.

Birds are also visible. You can monitor environmental changes by measuring population shifts in assorted species of mice and voles, but it's a real project, requiring time, patience, and a sizable research grant. By contrast, a birder with skilled, experienced eyes and ears can make a single slow pass through a patch of woods and come out feeling certain that he has noted a large majority of the birds present--and not just species, but individuals as well.

The biggest environmental monitoring scheme going is the National Audubon Society's Christmas Bird Count project. Every year during the holiday season, birders all over the U.S., Canada, and about 17 other countries conduct one-day bird censuses. Over 1,500 census tracts are now being surveyed--each is a circle 15 miles in diameter--and on many tracts the accumulated data cover several decades.

It takes many years for information like this to reveal its full value. A single count can be skewed in all sorts of directions by variables like weather, but over time these differences ought to even out.

Dave Johnson of the Evanston-North Shore Bird Club has compiled a summary of 24 years of results for the North Shore Christmas Count. The North Shore count covers an area bounded by Evanston and Lake Forest on the south and north and Lake Michigan and the Des Plaines River on the east and west. His summary is a formidable looking document. Three pages of very tiny print, each page consisting of a column of bird names on the left followed by 28 columns of figures that record the shifting numbers of North Shore birds between 1963 and 1986.

It's amazing what you can learn by following the ups and downs of an assortment of birds. In 1963, the North Shore count area was developed--mostly in houses and small commercial districts--near the lake. To the west, there were still lots of cornfields and vacant weedy grasslands. Today, the vacant lands and the croplands are almost gone and the count results reflect the change.

In the first five years of the count, '63 through '67, an average of 86 ring-necked pheasants was reported every year. In the past five years, '82 through '86, the average was 9. Eastern meadowlarks, common birds of the Illinois prairies, were reported on each of the first five counts, but they have been seen only three times since and the last sighting was in 1979. Marsh hawks, or harriers, also open-country birds, were seen seven times in the first 15 years of the count and not at all since. And horned larks declined from an annual average of 33 in the first five years to an average of four per year in the last five.

All this sounds quite bleak, and in fact it is, but some birds are managing to prosper through the changes. Consider, for example, the mallard duck and the Canada goose.

During the first five years of the count, the counters reported an average of 200 mallards per year. They saw no Canada geese at all until 1966, when they found one bird. They got ten a year later, and the explosion was on.

In the four years from 1983 through 1986, the average annual mallard count was 1,943. The average for Canada geese was 4,435! Two sets of events caused the explosion. The first was the introduction of the giant Canada goose into northeastern Illinois. In the 60s, geese passed through here in spring and fall. Now the giant Canada goose nests and winters here. The second trigger for the population surge was the arrival of the corporate pond.

The North Shore count area is filled with corporate headquarters and research labs set on fashionably campuslike grounds, and these grounds would not be complete without an ornamental duck pond, usually equipped with a bubbler to keep it ice-free in the winter. The ducks and geese live in and around these ponds, and when winter closes down their other options, they are so thick on the water that if you could step from one to another you could cross the pond without getting your feet wet. Huge geese waddle about the grassy banks, apparently traveling in family groups.

The North Shore is not all corporate ponds, of course. Much of it is covered with houses, many of them big houses on big lots, some set in woodlands by developers with enough sense of the landscape to leave the bigger trees standing between the buildings.

These suburban neighborhoods are now the winter home of a very large number of birds, most of whom are supported by backyard feeders. Thanks to an upsurge of interest in things natural and environmental over the past couple of decades, a substantial percentage of the people who live in upscale subdivisions have bird feeders in their backyards, and not surprisingly, that's where the birds hang out.

Walking through a winter woods, you're lucky to see 15 birds in an hour, but you can find twice as many all at once in many backyards.

The spread of winter bird feeding shows up plainly in the North Shore count results. Species that typically come to feeders are enjoying boom times. The black-capped chickadee, the ultimate feeder bird, expresses the trend most strongly. An annual average of 191 chickadees was reported in the first five years of the count. The last four years produced an average of 729 birds a year.

The pattern holds for goldfinches (92 to 316), cardinals (121 to 388), downy woodpeckers (100 to 157), and whitebreasted nuthatches (33 to 102).

Years ago Roger Tory Peterson predicted that the prevalence of bird feeders would change the distribution of winter birds. On the North Shore, it certainly seems to be increasing the populations of feeder species, at least during the winter. Next spring, this larger population will be competing for nest sites in the same old woods, woods that probably are near their carrying capacity already. We may be sustaining generations of maiden aunts and bachelor uncles, grouchy celibates who will spend their summers waiting for the holders of nesting territories to die.

Overall the pattern on the North Shore is the sort of thing you would expect in a newly urbanized environment. Cities typically support large numbers of individual birds--far more per square foot than the richest natural environments--but small numbers of species. City birds are often semidomestic, depending on humans to provide food and habitat. Both the mallard in the corporate pond and the chickadee at the backyard feeder fit that pattern.

But what is disappearing, on the North Shore and in most of the rest of the world as well, is the truly wild, the creatures whose presence is an expression of the essence of a particular place, the birds who would be there even if we weren't.

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