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.
Turkey vultures nest regularly just south of Cook County. You can find them every summer at the Kankakee Fish and Game Area and at Indiana Dunes, but the closest thing we have to a nesting record in this county is a statement by Robert Kennicott in an 1854 publication that they are “known to nest in Cook County.” If they have nested here since, nobody has noticed.
Vultures make a living by hanging in the sky all day and scanning the ground below for something dead to eat. They can stay airborne for hours and scarcely ever flap their wings. They do need updrafts though. The sun creates updrafts by heating the air near the earth’s surface: the hot air expands, gets lighter, and rises. Updrafts usually form over grasslands or plowed fields, places where the surface cannot absorb much heat. Forests create fewer updrafts because they can absorb lots of solar energy.
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.
While turkey vultures can be considered a reasonable possibility in Cook County, the red-breasted mergansers are totally unexpected. Their southernmost nesting area is around Green Bay, so the pair birder Ralph Herbst found this year along the Sanitary and Ship Canal are hundreds of miles from the rest of their species. They were successful in hatching young too. Any species can expand its range in this way. Only time will tell if this is an isolated incident that will not be repeated or the beginning of a new population.
This year’s nesting survey has lots of bad news for Mayor Daley. The Calumet marshes–which he wants to destroy to build his airport–produced endangered species in bunches. The pied-billed grebe, a small diving bird recently added to the state endangered list, nested at Big Marsh at 116th and Torrence, at Hegewisch Marsh at 134th and Torrence, and at Powderhorn Marsh off Brainard Street south of 138th. Double-crested cormorants were seen around Lake Calumet all summer. We have no proof of nesting, but they are apparently using the area as a feeding ground.
The least bittern, a small heron that spends its days sneaking around in cattails, also nested at Powderhorn. There were four active great egret nests in the Calumet marshes, and the endangered black-crowned night herons built more than 600 nests in the Big Marsh and more than 100 in other wetlands around Lake Calumet. Redheads, uncommon ducks, nested successfully at the Hegewisch Marsh, as did ruddy ducks.
Virginia rails nested around Lake Calumet, and so did the threatened common moorhen. At least 15 broods were discovered in five different locations.
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.
The marshes in the northwestern panhandle of Cook County were also very productive this year. Double-crested cormorants nested at Baker’s Lake in Barrington, as did great blue herons, great egrets, and black-crowned night herons. The nearby Crabtree Nature Center had at least one (endangered) black tern nest, three pied-billed grebe nests, and three broods of common moorhen. Fortunately, all these sites are part of the Cook County forest-preserve system, so the birds are likely to be able to continue to nest there without disturbance.
The mild winters we have been enjoying during the past several years continue to benefit the Carolina wren, a sedentary species that winters where it nests. We are at the northern end of its range, and the very cold winters of the late 70s wiped out the species in Cook County. But the wrens have been making a comeback. At least 13 pairs nested along the southern edge of the county in the Palos preserves, in Park Forest, at Sand Ridge Nature Center, and in the Plum Grove Forest Preserve.
The situation of Neotropical migrant songbirds is generally bad in the county, as it is all over North America. Wood thrushes were completely absent from the county this year, and veeries–a species of thrush–were extremely rare. A few reports of singing males came in, but there were no confirmed nesters.
There were only two reports of scarlet tanagers, and none of summer tanagers. Among warblers we had the yellow and the common yellowthroat, and not a whole lot else. A Louisiana waterthrush was seen feeding cowbird young at Palos, and we had reports of yellow-breasted chat, American redstart, and blue-winged warbler–and that was it. Among the possible species missed were cerulean warbler, black-and-white warbler, and ovenbird.
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.
With institutional support from Chicago Audubon, which can pay for mailings and publish the results of the surveys, Alan has started us on a significant conservation effort. Thanks to these surveys, we can say definitely which rare birds are breeding in the Calumet marshes. We can document the value of the Cook County forest-preserve system to local bird populations, and we can add our evidence on the status of Neotropical migrants to the bad news that is coming from the rest of the country.
As time goes on, we will be able to chart changes in the county’s bird populations. Birds, because of their mobility, are excellent environmental monitors. When things go bad, they can move out quickly. When things improve, they can invade quickly. They tell us, as well as any living thing can, what is going on.
This is also a good time to urge birders to get involved in nesting surveys. To my mind, a nesting survey is the most satisfying birding experience you can have. Locating nests and watching the young progress from eggs to fledglings provides a degree of access to nature that you just can’t get any other way. I suspect that any birder who tries it is going to get hooked on it. I’m sitting here writing in the middle of October, already daydreaming about what I’m going to be doing next June. Adding to the pure enjoyment of the task is the knowledge that nesting surveys are very important to conservation. They give birders a perfect opportunity to use their skills to benefit everybody.