A Eurasian tree sparrow has been coming to a feeder in the front yard of a house at 140th and Hoxie in south suburban Burnham. It began showing up regularly in mid-December, but its presence was not made known to the world until after the Calumet-Sand Ridge Christmas Count on New Year's weekend.
I went out in search of the bird on a brisk, sunny morning last week. My daughter Eleanor and I spent about 45 minutes standing on the sidewalk in front of the house studying a very large number of house sparrows and a somewhat smaller number of house finches that were hanging around the feeder, but naturally we saw no Eurasian tree sparrow. I say "naturally" because it seems to be my fate never to find rare birds that have been reported on the Chicago Audubon Society's Rare Bird Alert hot line.
If you call 671-1522, you can hear a recorded message telling you about interesting birds that have been seen around the region, but my failure to find any of these rarities has been so consistent that I'm beginning to think that Richard Biss, the ace birder who runs the hot line, is making all of them up. I can imagine him chuckling wickedly as he conjures up yet another exotic wanderer rare enough to lure local birders out into the cold to stare with shivering, futile intensity at mobs of house sparrows.
The staring is necessary, because house sparrows and Eurasian tree sparrows are very close relatives--both belong to the genus Passer--and they are quite similar in appearance. The tree sparrow is a slightly smaller bird, but the plumage of both sexes looks a lot like the male house sparrow's. The major differences are that Eurasian tree sparrows have brown crowns while male house sparrows have gray crowns, and tree sparrows have white cheeks marked with a dark spot while house sparrows have unmarked cheeks.
Like its familiar cousin, the Eurasian tree sparrow is an Old World bird whose natural range extends from Western Europe to Hong Kong. And like the house sparrow, the Eurasian tree sparrow was deliberately imported to this country during the late 19th century.
The place was Saint Louis. The year was 1870. A man named Otto Widmann provided this account of the introduction:
"Early in 1870 a Saint Louis bird dealer imported, among other birds, twenty Tree Sparrows (Passer montanus) direct from Germany. Mr. Kleinschmidt, hearing of it, persuaded Mr. Daenzer of the Anzeiger des Westens, who was at that time experimenting with the introduction of European singing birds, to contribute to the purchase of these birds. Accordingly they were bought and taken to Lafayette Park, in the then southwestern part of the city, and liberated April 25, 1870. All left the park immediately, and none were seen again until April 24 of the following year, when a single bird was seen one mile east of the park. This discovery was considered worthy of mention in the public press, since at that time the introduction of the European [tree] sparrow at Saint Louis was thought to be a failure."
Widmann goes on to say that the Eurasian tree sparrow established itself throughout the city, but increasing numbers of the more aggressive house sparrow--which were being imported at the same time--began to drive it from nesting boxes and the sheltered places under the eaves of houses, where both species prefer to nest. Within about a decade of the introduction, the tree sparrow, according to Mr. Widmann, "had to yield the city almost entirely to [the house sparrow] and betake himself to the country, spreading in all directions and resorting to tree-holes and out-of-the-way places, while the other took the cities and towns."
We could note in passing that the Anzeiger des Westens was apparently a German-language newspaper. German immigrants were heavily involved in bird importation. Their actions were seen as a sort of civic-improvement effort analogous to the founding of symphony orchestras and public libraries. Then as now, exposure to nature was seen as an uplifting experience, and "nature," to these newcomers, meant the plants and animals they knew in their childhoods in the old country.
The bird they knew as the European tree sparrow--the change to the more precise "Eurasian" was made within the last 20 years--did spread in all directions from Saint Louis, but it didn't spread very far. It can currently be found in a few counties in Missouri and Illinois. Its northernmost residence is Macomb, which is about 150 miles from Saint Louis. Vernon Kleen, an ornithologist with the Illinois Department of Conservation, describes its range in our state as an oval extending from East Saint Louis in the south to Macomb in the north, and from Springfield in the east to Quincy in the west. Jacksonville is the center of abundance.
Within this area it seems to have made its peace with the house sparrow. The two birds prefer to nest in holes, and they often nest very close to each other, whether on buildings or in holes in trees or in birdhouses.
They are both highly gregarious species, and within the tree sparrow's range can usually be found at this time of year in mixed flocks. According to Kleen, the flocks can contain almost any mixture of the two, from a 90-10 split dominated by house sparrows to a 90-10 split dominated by Eurasian tree sparrows.
Despite the socializing between the species, we have no indication so far that they are hybridizing.
Chicago Area Birds, the most complete record we have of bird sightings in this part of Illinois, lists only two sightings of Eurasian tree sparrows through 1983; since then, there have been one or two more. The species may be spreading north toward us, but if it is, it is doing so very slowly.
The case of the Eurasian tree sparrow shows once again how difficult it is to predict the consequences of introducing a new species into an ecosystem. The most common fate of any introduced species is death. The civic-minded sorts who gave us the Eurasian tree sparrow imported more than 200 other species that vanished almost as soon as they arrived.
Some imports, however, are so spectacularly successful in their new home that they become serious pests, decimating crops and driving out native competitors. The house sparrow and starling are our most famous examples.
And then there is a third fate. Some birds manage to establish themselves near the point of introduction, becoming a regular part of the avifauna in a small area but not spreading to colonize new places.
In some cases, this confinement to one small area seems obvious. South Florida is now home to all sorts of tropical imports, from the Java sparrow to the spot-breasted oriole. It is reasonable to assume that these species cannot expand northward because they can't handle the colder climate.
In other cases, we can only guess at why a particular species cannot increase its range. The Eurasian skylark, the sweet singer that inspired Shelley's ode, was introduced at Victoria, British Columbia, at the southern tip of Vancouver Island before World War II. It still lives there and on the nearby San Juan Islands, but it has not spread to any mainland location.
Introducing game birds has been the national sport of wildlife managers for the last 100 years. Because native species, such as Illinois' native grouse, the prairie chicken, have been driven out of vast areas by habitat destruction, managers have sought to import shootable birds that can survive in the devastated landscapes of postsettlement America. One of these introductions, the ring-necked pheasant, is well established over a very large range, but many other species show a pattern like that of the Eurasian tree sparrow. If you want to see the black francolin, an Asian partridge, you have to go to one small area in southern Louisiana. If you are looking for a Himalayan snowcock, you have to go to the Ruby Mountains in Nevada. The bird lives nowhere else in North America.
Small local populations are always vulnerable to extinction. Black francolins are suddenly quite rare in southern Louisiana, and in fact the species may have been wiped out there.
Nobody knows why the Eurasian tree sparrows have not spread. Certainly we humans can't see any barriers of terrain or climate to keep them from spreading. If they can live in Saint Louis and Springfield, it seems they ought to be able to live in Indianapolis or Cincinnati. But they don't.
Of course, their story is not over. Consider the house finch. Five years ago it was a big deal to see a house finch around Chicago, but now this is a common bird. At that feeder in Burnham where I searched futilely for a Eurasian tree sparrow, the house finches were almost as numerous as the house sparrows.
The house finch is a bird from the western United States that was introduced on Long Island about 50 years ago. For 30 years and more, it sustained itself on Long Island but did not significantly expand its range. And then about 20 years ago a population explosion began. Today you can find house finches in all the eastern states except Maine and Florida, and advance parties of the species are already well west of the Mississippi. In fact, they will soon join up with their long-lost brothers in the west.
For all we know, the Eurasian tree sparrow may suddenly enter a similar time of prosperity and expansion. Then I won't have to stand around in the cold in Burnham to see one.