At least 110 species of birds nested in Cook County in 1990. Five of them were exotics: pigeons, starlings, house sparrows, mute swans, and monk parakeets. The other 105 were natives.
Observers are supposed to place what they see in any of four categories. “Observed” is the most trivial. It just means that you saw a bird of a particular species during the nesting season. The hierarchy rises through “possible nester,” to “probable nester” to “confirmed nester.”
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To confirm nesting you need to see a nest occupied by young, eggs, or an incubating adult; recently fledged young still incapable of sustained flight; adults feeding young or carrying food to a nest; or nest building by adults of any species except wrens and woodpeckers. Wrens and woodpeckers building nests don’t count because male wrens build dummy nests that are never used, and woodpeckers may excavate several holes in trees before finding one they like.
Mute swans raised young in at least three locations in the county, and the uncommon hooded merganser bred in Glenview and at Crabtree Nature Center in Barrington .
Eastern bluebirds are another species making a comeback, thanks in considerable part to the creation of bluebird trails: a line of nest boxes placed at suitable intervals along a path. Bluebirds had declined, in part at least, because they lost both habitat and nest sites. They nest in cavities, and the arrival of the starling presented them with a formidable competitor. The nest boxes are made with entrance holes that are just slightly too small for starlings but big enough for bluebirds. We now have nesting pairs in 13 of the census blocks, and last year they produced at least 60 young.
Our most common sparrow, to nobody’s surprise, was the song sparrow, followed by chipping sparrow and field sparrow. We had two confirmed nesting pairs of grasshopper sparrows, but no confirmed nesters among the Henslow’s sparrows. However, there were singing males of this species in three locations. Both grasshopper and Henslow’s sparrows are prairie birds whose status is always a matter of anxiety, since nearly all their natural habitat is gone.
