A pair of turkey vultures nested in Black Partridge Woods near Lemont this summer, and a pair of red-breasted mergansers nested along the Sanitary and Ship Canal near Stickney.
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As you move north away from the equator and toward the poles, the amount of solar energy available to make updrafts declines, and this decline has a considerable effect on soaring birds. Turkey vultures can be found in small numbers as far north as southern Wisconsin, but our other species of buzzard, the black vulture, doesn’t live anywhere north of extreme southern Illinois. The controlling factor may be wing loading–that is, the ratio of wing area to body weight. The heavy-bodied and relatively small-winged black vultures couldn’t stay airborne in our cooler climate. The lighter-bodied, larger-winged turkey vultures can. However, north of southern Wisconsin the role of airborne scavenger is taken over by the much smaller raven. Apparently, the updrafts are just not sufficient to support big soaring birds in the north woods.
In a way, celebrating the presence of a pair of nesting turkey vultures in Cook County is artificial. If they had nested a couple of miles to the south, they would have been in Will County and therefore no big news. But in these times, even the slightest expansion of an animal’s range has to be taken as good news.
Thousands of birds occupied the ring-billed gull colony on an island in Lake Calumet this summer. The ring-billed is a long way from being an endangered species. You can see them soaring over shopping-center parking lots all over the Chicago area. But their colonial nesting habit makes them vulnerable. If the Lake Calumet colony were destroyed, the nearest nesting site would be at the north end of Lake Michigan, and the species would quickly go from abundant to rare in this area.
At this point, I ought to say a few kind words about Alan Anderson of the Chicago Audubon Society. Several years back Alan took on the job of organizing a continuing survey of Cook County’s nesting birds. This is an enormous task. He has had to locate people to do the job–there are well over a hundred now involved–and then nag them into actually doing it. And then nag them into submitting reports on their results. Having been late with reports a few times myself, I can say that as a nagger, Alan is kindly but relentless–just what is needed to get volunteers to perform. And once he gets all those reports, he has the huge job of compiling all the information they contain. For him, the nesting season doesn’t end until November.
