This is the time of year for migratory restlessness in birds and birders both. Migratory restlessness is the name ornithologists have given to the jumpy, nervous activity that keeps even caged migratory birds up all night in spring and fall. Hormones are behind it, stimulated primarily by changes in day length.
The bird doesn't know why it wants to move; it just knows it has to get out and go. Birders are equally in the dark about why they are obsessed with seeing birds, but they do know that this is the time to do it. Spring is great too, a season of hope that begins in the dim gray of March and ends with bright-colored warblers dancing through opening leaves and budding flowers. Fall lacks that hopeful quality. From Labor Day on, you know that things are only going to get worse. The days will get shorter, colder, and grayer; the birds will get scarcer.
But for a short time, fall offers more birds than you can see at any other time of year. There are two reasons for this. One is that the breeding season has just ended. Populations are at their peak with the young of the year added to the flock. The other is that there are more dumb birds in fall.
Spring birds are survivors. They are at least a year old. They made it through a long, hazardous migration flight the previous fall, and by the time they return to the latitude of Chicago, they are very nearly through another one. A few of them wander off course, but most of them stay on the route their species has been following for thousands of years.
In fall, many of the migrants are only a few months old and making their first migration flight. In most species, they are entirely on their own. The adults leave first, and the young of the year follow after them, finding their way as best they can.
Imagine a warbler born this July in a spruce bog in northern Ontario. He has never been more than 200 yards from the nest where he was born. One day as he is flitting through the treetops searching for bugs, his mom and dad fly by hollering "So long, junior. See you in Costa Rica." The kid is left to find his own way there. Needless to say, he probably won't make it. Most young migrants die along the way. They run into buildings; they get eaten by migrating hawks; they starve while looking for something to eat in inhospitable places like the Loop, or they get blown so far off course that they can never hope to find their way to their proper wintering ground.
This last group is what the birders are looking for. This is the time when hapless seabirds from the North Pacific get blown into Lake Michigan, the time when songbirds trying to get from Idaho to Chihuahua somehow end up in Chicago.
This year's big news in the "hopelessly lost bird" category was the rock wren that appeared a couple of weeks ago in the Magic Hedge at Montrose Harbor. For the nonbirders in the audience, I should explain that the Magic Hedge is a line of shrubbery that runs over the low hill that separates Montrose Harbor from Montrose Beach. Birders named it because of all the unusual birds that have been discovered in it over the years. Montrose draws migrants, apparently because they follow the lakeshore, and the harbor and beach are located on a peninsula. Once they land, the birds need cover and food, and the Magic Hedge provides both necessities.
The rock wren is a western species whose summer range extends no farther east than the badlands of South Dakota. As its common name implies, it is a bird of rocky places. It is especially drawn to arid, barren areas like old lava flows and talus slopes. In the heat of a summer day in such places, rock wrens may be the only visible life. The birds build their nests in natural hollows and cavities in the rocks. They are so enamored of this stony situation that they heap up pebbles at the cavity entrance and even weave small stones into the nest itself.
A bird that loves rocks that much is not going to feel at home in this part of the world. Our rocks are mostly buried under a hundred feet of glacial debris. If there was a bird called a mud wren, northern Illinois would be ideal for it.
In Chicago Area Birds, Steve Mlodinow lists only three previous records for rock wrens, all of them within ten days of each other. A bird was seen at Montrose Harbor on September 29, 1979, another at LaBagh Woods (around Foster and Cicero) on October 4, 1979, and a third at Illinois Beach State Park on October 8, 1979. There is at least a possibility that all of these sightings were of the same bird, or, somewhat more likely, that they were all part of a single small flock whose navigational apparatus wasn't working too well. The birders who saw this year's rock wren were witnesses to a phenomenon as rare as the appearance of Halley's comet and as unpredictable as a rainbow.
The rock wren was not our only rare bird this year. Downstate, near Springfield, some unusual gulls showed up. Sabine's gull, a bird that breeds on islands in the arctic and winters far out at sea in the Southern Hemisphere, was one of these. This species is much less rare than the rock wren. Mlodinow lists six records in the 70s and two from the early 80s. Nearly all this year's sightings were of immature birds, and nearly all the sightings were in October. We have records of only one spring sighting, and that was in 1873. It seems fairly plain that we are getting youngsters who have wandered off course. They may have come overland from Hudson Bay to Lake Superior, or they may have coasted eastern Canada and then followed the Saint Lawrence into the Great Lakes. Whatever the route they took to arrive here, they are going to need some luck to get back out to sea.
A black-headed gull was seen on Lake Clinton, which is an artificial lake near Clinton, Illinois. The black-headed is a Eurasian species that has recently invaded North America. It showed up first as a winter bird along the Atlantic coast. The first North American specimen was collected in New England in 1930. Recently it has begun to breed in Newfoundland. The first Illinois record was in 1973, and the first Chicago area sighting dates from 1976. Since then, it has become increasingly common as a fall and winter bird. If it continues to expand its breeding range, it may become a commonplace sighting.
We are also getting some sightings of jaegers, notably a pomarine jaeger on Lake Decatur. Jaegers are highly predatory relatives of gulls--the common name is the German word for hunter. The word was originally applied to wild hunters who lived along the Rhine and who were as much robbers and plunderers as huntsmen. The name fits these birds because they get much of their food by chasing smaller gulls and terns and terrorizing them into disgorging recently caught fish. The jaegers snatch the fish right out of the air and swallow it themselves. Like the Sabine's gull, the jaegers are arctic breeders that winter at sea. The few that pass through here in fall may not make it to their wintering ground, but perhaps they do.
Part of the appeal of watching birds is noting the changes--and the things that stay the same--in the natural world. This year's rock wren is probably an accident, an unfortunate individual blown off course. Perhaps it is a bird whose genes are messed up enough to impair its navigational abilities. If that is the case, we are looking at natural selection in action. This bird will not survive to return to the breeding grounds next year, and its faulty genes will be eliminated from the pool.
But things don't always work out that badly for wayward birds. A flock of fieldfares, European thrushes closely related to American robins, got blown off course in January 1937 and landed in Greenland. They established a colony there that continues to thrive to this day. Someday, it may serve as a jumping-off point for an invasion of the North American mainland.
The black-headed gull has already made that transition. The early sightings of winter wanderers were all of immature birds, perhaps out looking for a home of their own. Now that they have found one, they may spread to new breeding areas and establish themselves as common nesting gulls in the New World. If they do, birders will be the first to notice.