About 130 species of birds nested in Cook County in the summer of 1992. The dry weather of early summer made it a bad year for wetland species, but populations of some of our forest birds were up.
These generalizations are all based on the Cook County Nesting Season Bird Census, an annual survey of our nesting birds sponsored by the Chicago Audubon Society and compiled by Alan Anderson. This year the census period ran from June 5 to 15, and 111 observers sent in reports.
The county has been divided into 120 census blocks for purposes of the survey, and this year 81 of those areas received at least some coverage, including all but a few of our forest preserves. Most of the 40 uncensused tracts are city neighborhoods or suburban developments with little variety in their bird life. Leaving them out does little beyond slightly reducing the numbers of robins and starlings.
Robins, by the way, won this year's ubiquity award. Turdus migratorius was discovered in 80 of the 81 tracts. Runners-up were grackles (78) and cardinals (77). Mourning doves and red-winged blackbirds shared fourth place, with 76 each.
Our most common bird was the ring-billed gull, with more than 11,000 observed. Most of those were from the colony at Lake Calumet, where an estimated 5,000 pairs nested. Starlings took second with 3,599 individuals, and robins were third with 2,561.
These numbers have to be approached with caution. One of the nagging problems all bird counters face is how to compare species numbers. Ring-billed gulls are large birds that prefer to hang out in open areas, where they can be easily counted. Robins and starlings, while smaller, are quite bold and noisy and therefore easy to count. But the bird world is also full of skulkers--rails, cuckoos, wrens--that are very easy to miss.
Despite this caveat, a survey of the available habitats suggests that the census numbers are not too far off. The gull colony is surrounded by landfills. This is ideal habitat for ring-bills. Robins thrive across a range of habitats. They live in our densest woods and are equally happy in city and suburban neighborhoods, parks, cemeteries, and on golf courses.
Rails are wetland species that have a harder time finding places to live. As I said, all our wetland species had an off year. The lowest numbers in the eight-year history of the count were recorded for pied-billed grebes, rails, moorhens, and coots. Pied-billed grebes nested in small numbers at Palatine Marsh, at McGinnis Slough, which is in the southwestern corner of the county, and in various locations in and near the Calumet marshes.
Sora rails were reported in only four locations, only one king rail sighting was reported, and no Virginia rails were seen all year. Coots were reported at only three locations, down from 12 in 1991, and less than 30 birds were seen, compared to 100 in the previous year.
A short-term shift in population numbers probably doesn't mean much. It could well be that a rainy winter and spring would create a major rebound in 1993. However, several dry years in a row could reduce the breeding stock to the point that recovery might take a long time.
The miserable environmental conditions that assault almost all our wild creatures would add to the difficulties. Most of the marsh birds in Illinois live in the Chicago area. If a string of dry years seriously reduced the population, there would be no immediate source of replacements from anywhere nearby.
Carolina wrens continue to do well in the county. This year a pair nested in the Lincoln Park Bird Sanctuary, the fenced-in patch of woods and ponds behind the totem pole at Addison. Two pairs nested near the Sand Ridge Nature Center, and there were reports of singing males in various locations, including Glenview Woods and the River Trails Nature Center, which are both at the northern end of the county.
Carolina wrens are sedentary birds, which means they remain in one place year round. We are at the northern boundary of their range here, and the boundary shifts from year to year, depending on the winter weather. The really nasty winters of the late 70s wiped out the local Carolina wrens and shifted the boundary south of us. The birds have been slowly spreading back north during the past decade, but if forecasts of a very cold winter come true this year we may not have any next year.
At one time the eastern bluebird was completely extirpated as a breeding bird in Cook County, but in the past few years it has been making a comeback. All the known nesting locations this year were in artificial nest boxes put out to attract this bird. There were 25 confirmed nesters in eight different locations, and sightings of birds during the nesting season at six other places. The top location was the Little Red School House Nature Center in Palos Hills, where eight pairs nested. In our generally bleak environmental circumstances, the return of the bluebird is a small piece of good news.
The slight improvement in the number of forest birds is also heartening. Many of these birds are neotropical migrants, spending the summer here and the winter in the forests of Mexico, Central and South America, or the West Indies. Practically every species of neotropical migrant has suffered population declines over the past 25 years--some so drastic that we have reason to fear for their continued survival as species.
The veery, a thrush whose ethereal song is--in my opinion--the most beautiful of any American songbird, is on the threatened list in Illinois. This year we had 26 birds reported from 11 different locations, including nine singing males at one of the Palos forest preserves. Last year only 14 birds were reported from five locations.
Wood thrushes, which are pretty good singers themselves, were up too, with 102 birds reported from 27 locations, compared with 65 birds from 22 locations last year. The pair we discovered nesting at Somme Woods, where I help with the census, seems less surprising in view of these numbers.
Populations of vireos and warblers also showed some improvement. These small insect eaters account for most of the neotropical migrant species in our eastern woodlands. At least four, and possibly five, species of vireos nested in the county this year, including five pairs of Bell's vireos. This southwestern species is near the northeastern limit of its range here.
Among the warblers we had nine species classed as either confirmed or probable nesters, though we missed the Louisiana waterthrush and the cerulean warbler, both of which have nested here in the past.
Scarlet tanagers were discovered at 18 locations, and as many as 33 pairs may have nested. No summer tanagers were reported, but this is a southern species that only occasionally nests this far north.
Prairie species are among the birds we are concerned about. Eastern and western meadowlarks, bobolinks, and savannah, grasshopper, and Henslow's sparrows were the typical songbirds of our native tall-grass prairie. They remained abundant in Illinois long after settlement destroyed most of the prairies because they were able to adapt to living in pastures and hay fields. But since the 1950s they have all suffered declines of 90 percent or more as farmers have converted their pastures and hay fields to corn and soybean fields.
We still have fair numbers of these birds in the county, thanks to our forest-preserve system. Bobolinks were discovered in 18 different census tracts, and an estimated 144 pairs nested. Most of our meadowlarks are the eastern species, but we had two pairs of the western species recorded.
The Henslow's sparrow is an endangered species in Illinois, but we did have four pairs reported from three different tracts. Four pairs are a long way from a real population, but at least the species is hanging on.
We should all be grateful to Alan Anderson, who has worked like a dog compiling this census since it began eight years ago. And we should also thank the 111 volunteers who rose in the predawn darkness to go out and find birds. We can't make intelligent conservation decisions without good information. Birders are uniquely qualified to provide us with the information we need about the status of our bird life, and it is good that they are doing so.