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I've been spending many hours over the past few weeks computerizing all my observations from the breeding-bird survey at Somme Woods last summer. I bought some software called Bird Base 2, a spread-sheet program designed just for birders (one of several on the market), and entered each of the more than 2,000 observations I recorded in four months of work at Somme.

I have an antique computer, nearly seven years old, that accepts data the way small children eat oatmeal--slowly and with much groaning and grimacing. But I eventually got it all in, and the computer gave me stacks of printouts.

Somme is a 150-acre piece of the Cook County Forest Preserve District in Northbrook. It is a mixture of partially restored prairie, partially restored oak savanna, and young second-growth woodland that is beyond redemption. Restoration work began at Somme 15 years ago, and the breeding-bird survey is one of many monitoring efforts aimed at recording the changes stimulated by the restoration work.

We used a technique called spot mapping. We laid out a grid of observation posts in March, before there was much bird activity at the site. We made our surveys by moving from post to post recording all the birds we saw or heard during a six-minute stay at each post.

So my notes were a series of lists. At post B2 at 5:47 on the morning of May 29, I recorded two singing cardinals, a singing male yellowthroat, a singing male redwinged blackbird, a singing male red-eyed vireo, a brown thrasher, and a flicker. My new software lets me enter each list as a separate birding outing. When I print all this out as separate lists for each species, with observations from all the posts listed chronologically. I am now plotting all these observations on maps--one map for each species--so I can see both the numbers of breeding pairs for each species and their distribution in the preserve.

Most of what I am learning from this process is stuff I already knew but couldn't prove until I could lay out the data in this form. My maps are telling the story of a community of birds concentrated along the edges of wooded areas or in the small clearings surrounded by woods. We had some good species in the woods this year--wood thrush, red-eyed vireo, eastern wood-pewee--but in general the woods are much quieter than the edges and clearings. There are fewer species and fewer individuals.

Some of what I'm learning is new and unexpected. Consider the crows. In early spring crows are the most visible birds. They seem to be everywhere. In early April I was recording as many as ten sightings each visit, some flying, some perched, sometimes a pair chasing each other as if in a courtship ritual.

I saw a bird carrying a fairly substantial stick-nesting material--on the 11th of April, and by the end of the month we had located four nests. I had a pretty good idea of the location of a fifth, though I never found it. On May 6, I saw seven birds, but then the numbers started to fall. By the end of May I was seeing only one or two birds a day. In the first half of June I recorded only seven birds in nine visits, and in the last half of the month, five birds in seven visits.

Where were the crows? Had some of the birds of spring left to spend the summer elsewhere? Or were the birds just less conspicuous because they were quietly engaged in raising young instead of wandering in search of a good nesting site or courting noisily? Or was it a little of both? Later in the summer they would appear again in flocks that would grow larger as winter approached. Were they returning from somewhere or just getting out more often?

The people who develop standardized methods for surveying bird populations are tormented by problems like the disappearing crows. How do you deal with the fact that certain birds are more conspicuous than others, and that the same species may be more conspicuous at one time than at another? Breeding song sparrows sing over their territories for weeks on end. It is a fairly simple matter to figure out how many pairs are present. But last year our cedar waxwings just moved into an attractive area and immediately started building nests. They didn't sing, they didn't defend territories--they just nested and moved on. If I hadn't happened to be in the right place at the right time to see waxwings with grass stems in their beaks, I might never have known they were there.

Black-capped chickadees seem to prefer building their nests in the broken-off stubs that remain after the trunk of a standing dead tree has been blown down. Six of the seven nests I found were in such situations. Chickadees nest in holes in trees, and they generally excavate their own holes. A recently deceased tree with its tall, solid trunk still standing may be too hard for the tiny bills of these birds. They may seek the stubs because the wood is more likely to be soft and rotten, and therefore removable.

House wrens are another hole-nesting species that should find lots of opportunities at Somme. The restorers are converting the second-growth woods to prairie or savanna, and they remove the trees by girdling them. Girdling kills trees but leaves them standing to provide nesting and feeding sites for many birds and mammals.

We had six or seven pairs of house wrens this year. They like woodland edges, but they will move well out into fairly open areas if there is a good nest site--a standing dead tree with some holes either rotted in it or dug by woodpeckers.

Yellow warblers like dense brush. They live in brambles or thickets of gray dogwood. This year at Somme we had nine pairs. And we had as many as 13 pairs of another thicket bird, the gray catbird.

I found it surprising that there were almost as many catbirds as there were cardinals--at least according to my data. Cardinals, which sing from midwinter until July, are so noisy and so visible that they make a much stronger impression than the rather retiring catbirds.

I'm still struggling with the data on red-winged blackbirds and robins. One of these may be the most numerous species at Somme, but it is very difficult to tell for sure. Red-wings are polygynous, and in suitable habitat males may gather several mates that all build their nests in a very small area. So one singing male may account for two or three nests.

Robins are very unpredictable in their nesting behavior. Males sometimes proclaim their territory with long stretches of song. But sometimes they don't. Sometimes a pair will attack any strange robin that dares to enter their nesting territory, and sometimes they ignore trespassers. So what I have are hundreds of sightings that I have to piece together to get some kind of picture of this bird's population. I don't expect a high level of certainty on this one.

And then there were those nests. As early as the end of April we found robins building nests all over Somme. The nests were usually in exposed situations. The horizontal trunk of a downed tree was a typical site. You could see these nests from 30 feet away. And within a week of our discovering them, every one of these early-nests was abandoned. I don't think any eggs were laid in any of them. So what was going on here? Were these some kind of dummy nests? Or were they just cases of bad judgment, nests built in unsafe situations where there was almost no chance of success? I don't have any idea.

The song sparrows are a wonderfully unambiguous bunch whose habits make them an ideal subject for the census taker's art. They settle down early in nicely defined territories, and the males sing loudly and frequently. We had 20 pairs of breeding song sparrows at Somme last year, according to my records.

The song sparrows avoided totally treeless areas, but it didn't take much in the way of woody plants to attract them. They lived in and around dogwood thickets, but they also nested on prairies where there were only a few small hawthorns or other shrubs about.

We had only one singing male field sparrow at Somme this year. Open fields with a few small trees for singing perches apparently work as habitat for both song and field sparrows. It would be interesting to try to figure out how they divide up the habitat. Of course this is only one of the thousands of questions raised by these stacks of printouts. I don't think I'm going to run out of new things to study at Somme.

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