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Our greenhouse spring hit with full force last weekend. Warm temperatures and south winds have been bringing early migrant birds in since the end of February, and by last weekend birders were reporting 20 species of ducks at Palos. I heard a white-throated sparrow singing along the Chicago River. There was even a catbird sighted in the area.

At Somme Woods in far northern Cook County male red-winged blackbirds, song sparrows, and cardinals are already singing. Woodcocks are there in numbers. Bill Valentine visited Somme at twilight last Sunday and located at least five of the birds in the eastern half of the preserve. They were calling to each other but had not yet begun their display flights.

The woodcock's twilight display is an impressive show. The birds fly straight up while giving a twittering cry. At the apogee of their flight, they set their wings in a half-open position and drop lightly back to earth, falling in little swooping glides like leaves dropping from trees.

The display is also a good example of convergent evolution. Woodcocks are sandpipers that have adapted to life on the ground in wet forests and along forest edges. Though they are not at all related to grouse and turkeys, their display is the beginning of mating behavior very much like what grouse and turkeys use. The male sets himself up on a display site--called a lek--attracts as many females as possible, mates with them, and then takes no further part in producing or caring for the young. The female makes a nest, incubates the eggs, and then protects the young until they are big enough to fend for themselves. Apparently this method works for large terrestrial birds, and it has evolved in two widely separate groups.

I have been censusing nesting birds at Somme for three years, but this spring I have been getting to know the place far more thoroughly than before. Working with Bill Valentine and Beverly Hansen, I have been laying out a grid of observation posts from which we can see and hear all the nesting birds on the 150-acre preserve.

Grids like these are used regularly by scientists surveying nesting species. Our grid places the observation posts 150 meters apart and at least 75 meters in from the nearest edge. Many studies use larger grids, and some put their observation posts as much as 300 meters apart. Somme is bordered on three sides by very busy roads and there is always a lot of ambient noise to contend with, so a small grid gives us a better chance to hear every song sparrow and blue- winged warbler in the preserve.

We laid out the grid with the aid of basic rock-and-roll surveying instruments. I taped a compass to the top of a camera tripod to point a direction. Bev carried an aluminum tent pole with a piece of bright-colored ribbon tied to its top. She walked in the direction of my compass heading, and I hollered and waved my arms to direct her to the spot my compass showed to be correct. Bill got the lousy job. Starting from my tripod, he had to unroll a 50-meter tape measure toward Bev so we could measure distances with a reasonable degree of accuracy.

Pulling a measuring tape through dense brush is not easy. Sometimes you have to crawl on your hands and knees to get through the really dense stuff. And somehow we seemed to find every multiflora rose and every blackberry patch in the whole preserve, so Bill got stabbed fairly regularly.

We marked our observation posts temporarily with tent stakes and bright-colored ribbons. Our permanent marks are little piles of gravel supplied by the Forest Preserve District. Last Sunday Bill and I hauled gravel all over the preserve. Our technology for this operation was pre-Columbian. We each filled a bucket with gravel, hoisted it on our shoulders, and walked--often through thick brush--to the previously surveyed observation posts. Gravel is very heavy. And after you have schlepped a bucket several hundred yards through buckthorn thickets it gets even heavier. Bird-watching is hard work.

We have learned a lot from this experience, however. We have examined every part of the preserve with a thoroughness we never achieved before. There is one little triangle of woods bordered by the river, the railroad tracks, and Dundee Road that I had never even looked at before. Now it has a small pile of gravel right in the middle of it, so we will be checking it out regularly for the next three or four months.

We also found two fresh deer carcasses and lots and lots of skulls. We found a good-size deer skull complete with antlers that looked ready to model for Georgia O'Keeffe. We found a woodchuck skull, the remains of an animal that had apparently survived for some time after it stopped eating. The incisors of woodchucks--like those of all rodents--grow continuously, and constant chewing keeps them the proper length. This animal's incisors were grotesquely elongated. They looked like the tusks on a walrus.

And we found fox skulls and raccoon skulls, and scattered here and there the odd pelvis or rib bone. Inch-by-inch surveying gives you a strong sense of how many things are out there dying.

The red-tailed hawks that nested at Somme last summer have hung around all winter. Lately we have seen them bringing sticks to last year's nest. We hope this means they are rehabbing the old structure to get it ready for another season.

Lay out a grid of observation posts 150 meters apart and 75 meters from the nearest edge at Somme and you come up with a total of 32 posts. You do a survey by moving from post to post and staying at each post for a certain period of time. We are allowing six minutes at each post. Birds do not sing constantly, but given six minutes almost all territorial males will announce themselves with a song at least once.

Of course birds sing mainly very early in the morning. If you have 32 observation posts to cover and give each post six minutes, it will take you 192 minutes. Add in travel time between posts and you are looking at four to four-and-a-half hours. So trying to survey the whole place in one morning is not a very sensible way to use your time. We have divided the preserve into three sections, two with 11 posts and one with 10. If we do one of these each morning and set up our schedule so that each area gets covered equally, we should discover just about every nesting pair on the preserve.

Early on the morning of Saturday, March 14, we will make our first official survey of one-third of the preserve. If we can stay on our schedule, every part of the preserve will be surveyed once or twice a week every week from now until about the middle of August, when the last late-nesting goldfinches will be accepting the responsibilities of parenthood.

Many, probably most, active birders are collectors. They collect experiences, sightings of species of wild avians. I have never been a collector. For me birding is a chance to try to figure out what the hell is going on out there, which is why most of my birding involves surveying nesting birds rather than chasing migrants. Nesting birds give us real information about the state of the environment. Sightings of migrants are largely a question of luck. It is hard to draw much meaning from them.

At the same time, I find it weird that I am setting up this really precise system for doing the surveying. I am a seriously antibureaucratic person. I stick with free-lancing because I just can't stand the routine of going into an office every day. When nesting season comes, all I really want to do is hang out in the woods and find nests. Yet here I am with a tape measure and a compass trying to nail down the exact numbers of breeding birds at Somme Woods. And I'm instructing other birders who are doing their own surveys to follow my example, something many of them don't want to do. My free-spirited exterior seems to hide a closet Stalinist or maybe the sort of person D.H. Lawrence called a "ghastly, obscene knower," a person who wants to shine the light of reason on all the dark mysteries.

OK that's what I am. A 20th-century man. But reason is only a starting point. It is a way for those of us who cannot believe in spirits to enter into communion with nature. And the secret is that if you stay at it long enough, if you have patience, if you can wait for nature to show you what it is, you will leave reason far behind.

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