Nesting mockingbirds are not major news in most of the United States. Northern mockingbirds--to give them their full, official title--are not only common, they are conspicuous. South of the Ohio River, practically every backyard has its nesting mockers, and the birds sing for much of the year. During nesting season, they may sing all night.
But Chicago is on the border of the species's range. Like most such borders, this is more zone than line. Peterson shows the range extending into southern Wisconsin, indeed along the lake as far north as Door County, but populations would be very sparse that far north. In the Chicago area, the bird is far more likely to be found around Joliet or Kankakee than Waukegan. But the rare-bird hot line (671-1522) reports sightings at Illinois Beach State Park near Waukegan. Given the season, it's likely the birds are nesting.
American mockingbirds were first made known to science in 1709 in A New Voyage to Carolina by John Lawson. Although this book attracted little attention, Lawson subsequently contracted to do a more complete natural history. The project came to an abrupt end when Lawson was captured and killed by Tuscarora Indians.
Mark Catesby was another pioneer in the days when men could call themselves natural historians and collect and classify everything from dragonflies to rhododendrons, without worrying about specialization. He incorporated some of Lawson's observations into his own Natural History of Carolina, Florida, and the Bahama Islands, published in a series of volumes between 1729 and 1747. Catesby's color engraving and his written description of "the Mockbird of Carolina" served as Linnaeus's source for classifying the bird and naming it Mimus polyglottos, the many-tongued mimic. Catesby noted that the Indians called it cencontlatolly, which he translated as "four-hundred tongues." Mockingbirds were apparently as common around Indian towns as they are now around the towns of the Indians' conquerors.
Their talent for mimicry is amazing. They regularly imitate the songs and calls of dozens of different birds. A single mockingbird was once heard to mimic 32 other species in the space of ten minutes. And they don't stop with other birds. Frogs, crickets, squeaky wheelbarrows, even pianos can be part of the repertoire. These imitations are not half-assed efforts. Even electronic analysis cannot separate them from the originals.
Mockingbirds are members of a New World family called the Mimidae, the mimic thrushes. We have two other species in this area: the gray catbird and the brown thrasher. Both are quite common species whose ranges extend north to Lake Superior and beyond.
Mimic thrushes tend to have long tails and short, broad wings, a design that produces flyers capable of fast starts and a high degree of maneuverability. The design well suits their preferred habitat: brushy areas and woodland edges where the plant life is dense and tangled.
The gray catbird is a plain creature, gray all over except for a black cap and a bit of rusty red under the tail. Brown thrashers are bright rusty red above, and white streaked with brown or rust below. Mockingbirds are mainly pale gray with a flash of white in the tail and wings.
All three species are mainly ground feeders whose preferred food is insects. Mockingbirds will raise their wings as they hunt over the ground. The movement is believed to flush insects, and it also makes it easy for birders to see the patch of white in the gray wing.
Catbirds and brown thrashers are very good singers and accomplished mimics, although they don't do quite as much imitation as mockingbirds. The length and variety of their songs are features that set all these mimic thrushes apart from other families of songbirds. Wood thrushes and veeries, for example, sing songs of ethereal beauty, but they essentially repeat the same brief phrase over and over, and each performance lasts no more than a couple of seconds.
Mimic thrushes can rattle on indefinitely with an endlessly varied succession of single notes and long phrases that is immediately and obviously different from the songs of any other family. The challenge for birders is not to separate mimic thrushes from other families but to differentiate the songs of our three local mimic thrushes. The books all say that catbirds tend to sing each phrase a single time. Brown thrashers are said to repeat each phrase once, and mockingbirds reprise each idea several times.
In the field, you will encounter birds who haven't read the books. Or maybe you will encounter a catbird displaying its skill at mimicry by imitating a brown thrasher. I always try to see the birds to check on any identification arrived at by ear.
Mimic thrushes live only in the New World. The 31 species range over both Americas, but the center of their abundance is the southwestern United States and northern Mexico. My field guides to Colombia and Venezuela list only four species of Mimidae between them, and one of those is our familiar gray catbird, which winters in Colombia. Another is the tropical mockingbird, which ranges from southern Mexico to Brazil. The American Ornithologists Union, in its wisdom, has given North American mockers an official name that separates them from the tropical species. Thus, here in the United States, we must refer to the bird most identified with the old south--four states there have named it their official bird--as a northern mockingbird.
In the west, you can find seven different species of thrashers, six of them members of the genus Toxostoma. Toxostoma means "bow-mouth" and refers to the long, curved bills that are among the most striking characteristics of the thrashers. Their common name probably comes from their habit of using their bills to toss aside leaves and other litter as they hunt over the ground. This reminded people of a farmer tossing hay with a fork.
Some of the thrashers are quite local in their distribution, none more than the aptly named California thrasher, a bird that lives mainly in the chaparral hills, the scrubby landscape that keeps threatening to burn LA. California thrashers live only in the Californias, baja and alto. In Life Histories of North American Birds, A.C. Bent describes their range as extending from "the western slopes of the Sierra Nevada and the higher mountains of southern California to the Pacific, and from the head of the Sacramento Valley to about latitude 30 degrees in Baja California." Deserts and high mountains are the obstacles likely to have prevented the California thrasher from expanding eastward.
California thrashers are sedentary birds, remaining pretty much in one place year-round. Brown thrashers retire to the southern states in fall. A few catbirds linger along the gulf coast, but most of them leave the United States to winter in the tropics.
Mockingbirds are sedentary. Indeed, they sing in the fall in order to establish an exclusive feeding territory for the winter, a territory they defend as vigorously as they do their summer nesting territory. Their settled ways are probably to blame for their inability to expand as far north as their migratory relatives.
However, they have been expanding their range into southern Ontario and New England over the past several decades. Some authorities believe that the northernmost birds withdraw from their nesting areas in fall and spend the winter in more hospitable climates. As ground feeders, they cannot make it where snow persistently covers their food.
Their northward expansion may also reflect habitat changes created by humans. Neighborhoods of houses and yards look pretty much the same in northern Illinois as in Tennessee. Mockingbirds regularly come to feeders after raisins, bread, and suet, so the increasingly widespread practice of putting out feeders for birds may be helping mockingbirds maintain themselves here in the frozen north. We won't ever have magnolias or live oaks festooned with Spanish moss, but maybe someday we will hear mockingbirds announcing the coming of summer by imitating a squeaky wheelbarrow.