Field & Street 

A loggerhead shrike recently spent several days at Montrose Harbor. I had the good fortune to see the bird on Sunday, March 29. Montrose has long been famous as a rich source of sightings of rare--and, for that matter, common--species, especially during spring and fall migration. The loggerhead shrike was just the latest in a long line of good sightings. The fact that it stuck around for a considerable time is further testament to the large number of birds that move through the lakefront site. A bird that eats birds would find a lot of food at Montrose.

Shrikes are songbirds. They are related to mimic thrushes, such as the mockingbird, and to warblers, vireos, and other inoffensive insect-eating singers. But shrikes have taken a different evolutionary path than these close relatives. Shrikes are predators. They certainly eat insects--especially larger types such as grasshoppers. But a significant amount of their food is vertebrates, especially mice and small birds. Their predatory path has produced some habits and some physical structures unique to shrikes, but it has also revealed a key fact of life. Whether you are a human being or a bird, you can't escape history.

Shrikes are predominantly Old World birds. Africa seems to be the place where they originated. Of the 74 species in the family, only two live in North America, and one of those is the northern shrike, which lives in the coniferous forests that circle the world in the higher latitudes. The loggerhead is the only shrike that is confined to North America.

The plumage of both of our shrikes is very similar to that of the mockingbird, and in some areas of the south the local name for the loggerhead is French mockingbird. Why it should be called "French" is a mystery. White, black, and gray are the colors. Both shrikes and mockingbirds have black wings and tails with patches of white. Shrikes have black masks around their eyes, a common feature in birds whose way of life requires them to see movement at a distance.

The plumage aside, the two birds look nothing alike. Mockingbirds are slender birds. Shrikes are built like linemen: thick necks, barrel chests, big heads. Mockingbirds have rather long beaks with a slight downward curve. The beaks of shrikes are thick, and only the upper mandible is hooked. Shrikes are also slightly smaller than mockingbirds. A loggerhead shrike is not even as large as a robin. A big male might weigh as much as two ounces, but most loggerheads are lighter than that. Yet these small songbirds take such prey as bluebirds and meadow voles, animals nearly as big as they are and not without defenses.

The French anthropologist Claude Levi-Strauss wrote extensively on mythology. The creation of myths, the stories we use to explain the workings of the universe, he wrote, proceeds like the work of a traditional handyman. The handyman carries with him a bag full of miscellaneous parts. He uses those parts on the job at hand and often parts that were designed for one purpose end up being used for a completely different function. So concepts and fragments of stories from many sources may be combined into a mythological tale that has little to do with the sources of those concepts and stories.

Evolution operates in much the same way. Natural selection can thicken the beak of a shrike and turn a tool that once functioned as a tweezers for plucking insects into a device for pulling strips of breast meat from the bodies of chickadees. But natural selection cannot create a whole new structure. However far it proceeds in the direction of becoming a bird of prey, a shrike cannot escape its history as a songbird.

The feet are the clearest illustration. Both hawks and owls have powerful talons, strong curved claws controlled by major muscles. Their feet are their principal weapons. They clasp the prey and squeeze it until it stops struggling. The beak does no more than administer the coup de grace.

A shrike's feet are strong for a songbird. Shrikes can carry prey in their feet, and they can use their claws as weapons. But they still have songbird feet, feet whose principal function is to curve around a tree branch. A peregrine falcon capturing a pigeon in flight grabs its prey with its feet. A shrike nailing a dragonfly in the air captures its meal with its beak. A shrike on the ground trying to dispatch a mouse also uses its beak. If it tried to use its feet it might just get bitten. The shrike-mouse combination is a small-scale version of a lion and a zebra. The lion has to be very careful in its attack because the zebra can deliver a fatal injury if the lion is the least bit careless. A shrike will circle a mouse on the ground looking for an opening that will allow it to deliver a blow without putting itself at risk. For a predator as small as a shrike, a mouse is a serious adversary.

Those songbird feet could be the source of one of the most striking aspects of shrike behavior: the habit of impaling prey on thorns. A red-tailed hawk can easily hold down a rabbit with its talons while it strips away hunks of meat with its beak. A shrike may need a little help, so it makes use of thorns. Impaling things on thorns also allows the shrike to store food when times are good and eat it when times are hard.

The shrike at Montrose Harbor was eating a small bird when I and several other birders saw it. The shrike was perched high in a tree; the small bird--in the absence of thorns--was wedged into the crotch at the base of two small branches. The shrike was eating the small bird from the head down, tearing off chunks of meat, feathers, and bone and swallowing each chunk whole. Like other birds of prey, shrikes vomit the indigestible parts, the feathers and bones.

The loggerhead shrike was a bird of savannas and woodland edges in presettlement Illinois. Shrikes hunt from perches on trees or tall shrubs, but those trees and shrubs must be at the edges of open areas. Shrikes have evolved the keen eyesight of birds of prey and can see a bumblebee 300 feet away. Tests with caged mice show that shrikes can detect a moving mouse on the ground 600 feet away.

Loggerhead shrikes enjoyed a brief moment of prosperity in Illinois after settlement. Farmers out on the prairie planted hedges to divide their fields, and the most popular hedge plant was a small tree imported from Oklahoma called the Osage orange. Osage oranges, which my grandfather the farmer referred to simply as "hedge," have very long thorns. Shrikes found themselves in an environment where small trees with long thorns--trees that made ideal perches and ideal places to impale prey--surrounded open fields that were perfect hunting grounds.

The hedges came down in the late 40s and early 50s, and just about that time Illinois farmers switched from generalized farming to specializing in corn and soybeans. The pastures and hay fields that provided the shrikes with savanna sparrows and fat grasshoppers became corn and soybean fields sterilized with chemicals. Times got hard for the loggerhead shrike. By the 1970s the central Illinois populations had largely been eliminated, and the species was designated "threatened" in the state.

In northeastern Illinois the loggerhead shrike is currently known to nest in the Midewin National Tallgrass Prairie near Joliet. As that site is restored to native vegetation, the needs of the shrike will be of special concern. In the meantime, sightings of loggerhead shrikes will be rare and eagerly sought after.

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