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Last week 200 great egrets were counted at McGinnis Slough, along with 100 double-crested cormorants. This is the sort of sight people travel to the Everglades to see, but if you are not an active birder you may be surprised that such a concentration of these spectacular waders could show up in Cook County.

Great egrets are long-legged, long-necked birds with snowy white plumage and daggerlike yellow bills. They hunt in shallows, capturing small fish, frogs, snakes, crawfish, snails, and assorted other small creatures with lightning-quick stabs of that long beak.

At the turn of the century egrets had been hunted nearly to extinction. Their long, delicate nuptial plumes were a favorite decoration for ladies' hats. In 1903 egret plumes were bringing $32 an ounce, which was about twice the price gold brought. Since these nuptial plumes grow only in the breeding season, hunters had to attack the birds on their nests. They killed the adults and left the young to starve.

The campaign against the feather trade was the first big undertaking of the National Audubon Society, and a great egret still serves as the official society emblem. Thanks to strict protection, the bird has come back over its historic range, but wetlands destruction has kept it rare in Illinois.

McGinnis Slough is a vast shallow lake in the town of Orland Park in the southwest corner of the county. It is owned by the Cook County Forest Preserve District. There is a parking area just off U.S. 45 between 131st Street and 143rd Street that provides access to the eastern side of the slough.

McGinnis Slough was once a cattail marsh, but back in the 30s a box culvert was installed at the marsh's outlet to control water levels. This structure was improved in the 50s.

The Forest Preserve District manages McGinnis solely for wildlife. No boats are allowed on its waters; no fish are stocked. The culvert allows the FPD to manipulate water levels for maximum wildlife benefit. Near shore, where the muck bottom supports cattails, rushes, sedges, and other emergent vegetation, marsh birds nest and muskrats build their houses. This year pied-billed grebes, common moorhens, and yellow-headed blackbirds all nested at McGinnis, and least bitterns were seen during nesting season and may have nested.

News of successful nesting by these species is always welcome. Pied-billed grebes used to nest in every little pond in the midwest. Most of the little ponds are gone, and--even more alarming--the grebes don't always show up in the remaining suitable habitat.

Grebes are a delight to watch. They dive for their food, which is a mixture of the small creatures likely to be found in a marsh--small fish, frogs, crawfish, leeches, aquatic insects, and worms--and they can stay underwater for long periods. They usually dive headfirst, but they have such perfect control over their buoyancy that they can sink slowly out of sight without making a ripple, and they can swim with only their heads and necks above the water.

The common moorhen is a lovely bird with a stupid name. It is a rather chickenlike creature with a bright red bill topped with an equally bright red facial shield. The shield is a sort of extension of the bill that forms a flat plate that covers the bird's face up to the forehead. Moorhens are excellent swimmers whose large feet are lobed rather than webbed. The toes are separate, but each has paddlelike lobes along both edges that help push the bird through the water.

Until a few years ago we called these birds gallinules, a name that means something like "small chicken." It was a fairly accurate description of their general appearance. Then the American Ornithologists Union decided to force Americans to conform to British usage (the bird also lives in Europe) and adopt the name "moorhen." I find the general idea of conforming to British usage offensive to begin with. We won the battle of Yorktown, and we should not be required to conform to anything that happens in Maggie Thatcher's semifeudal hellhole. Also, we don't have any moors here, so how could we have a moorhen? If they really had to change the name, they should have changed it to "marsh hen."

The moorhen is a threatened species in Illinois, one of the many casualties caused by our destruction of wetlands, so news of its breeding here is always good. Yellow-headed blackbirds are considered endangered in the state. They did not nest at McGinnis when I first started going there 16 years ago, so their expansion into new nesting territory is another piece of good news.

McGinnis Slough is also the place where black rails were last seen in the Chicago area. This happened a couple of years ago on the statewide spring bird count. Black rails are tiny marsh birds whose habits are so reclusive that nobody can say for sure where they nest or how rare they are. We do know that the marshy places at McGinnis are just the sort of thing they prefer as a nesting ground, so it could be that they are there every summer. We may never know.

The paved parking lot off U.S. 45 is not the only way to get into McGinnis Slough. There is a sort of back door on the western side. You leave your car at the roadside at the corner of 108th Avenue and 139th Street and walk in along the remains of an old road. I am not 100 percent sure that parking is legal at this place, so if you try it, you are on your own. If you get a ticket, it's your problem.

You will also get your feet wet, especially with the weather we have been having. But once you get near the slough itself, you can sit in a lovely old oak grove and look out over the water. This place was better in 1974 when my wife and I first visited it as part of our honeymoon trip to romantic southern Cook County. In those days the ground under the oaks was open and grassy, and you could lie back and take your ease while watching the birds on the slough. Now buckthorn, that vile alien shrub, has invaded, and it is much harder to see anything and much harder to find a space big enough to lie on that is not covered with buckthorn stems.

We also found another good entrance to the slough along 143rd Street, but this one is thickly posted with No Parking signs, so I won't give any more details about it. We found it while looking for a way to get to the south shore of the slough. We wanted to get there because if you are looking through a spotting scope at birds far out on the water, the visibility is much better with the light behind you. Dense buckthorn growth has made it almost impossible to skirt the edge of the slough unless you are prepared to crawl on your belly.

At this time of year the FPD lowers water levels in the slough to create mud flats that attract migrating shorebirds. The mud flats also allow smartweed and other annuals to sprout. In the fall water levels will be allowed to rise again. Migrating ducks will use the slough then, with the vegetarians among them feeding on the smartweed that grew on the mud flats.

Birders know McGinnis as a great place to see migrating ducks, geese, loons, and grebes. We can also expect sightings of ospreys and bald eagles.

The great egrets and cormorants we are seeing now at McGinnis are postbreeding wanderers that may have come from almost anywhere. The closest nesting colony for these two species is at Lake Renwick near Plainfield. The lake is an old sand and gravel quarry that provides a nesting home for several rare water birds. In addition to the egrets and cormorants, which are both on the state endangered list, the endangered black-crowned night heron nests there, and the endangered snowy egret is also sometimes seen.

Lake Renwick was in private hands until recently. But now, thanks to a combination of county, state, federal, and private--through the Nature Conservancy--money, it is part of the Will County Forest Preserve District, so its rookeries will be protected.

The hope is that some of its rare species will expand into McGinnis Slough, adding a nesting colony to their range in Illinois. Great blue herons are already nesting at the slough. Those dense thickets of buckthorn are helping to maintain the seclusion the birds prefer. There has been discussion of building some nesting platforms at McGinnis to accommodate species such as the great egret. It would be lovely to see them there in June as well as August.

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