Last week I was in southern West Virginia for the New River Birding and Nature Festival. On Wednesday evening Paul Shaw, a local birder and field trip leader, showed me a photo on his digital camera. It depicted an adult male red-winged blackbird impaled through the throat on a barbed wire fence.

"Loggerhead shrike kill?" I asked. "I think so, but we couldn't find the bird," Shaw replied.

The next day I joined a group that visited the same area, so I was anxious to see if the shrike victim was still on the fence. It was. The habitat consisted of pastures, rolling hills and scattered trees, reminiscent of shrike habitat I know from my years in Oklahoma. We looked and listened for shrikes for about 20 minutes, but had no luck. But an impaled red-wing, essentially the same size as its predator, is pretty solid evidence of shrikes.

At a glance, loggerhead shrikes are gray and resemble northern mockingbirds. When I taught ornithology in Oklahoma, students would invariably remark, "... but it has white wing patches like a mockingbird." After insisting they look closer, they'd respond, "Wait, its wings are much darker than a mocker's, it has a black mask, and the bill is hooked like a hawk's." After just a few minutes, the entire class agreed that, while superficially similar to a mockingbird, the loggerhead shrike was easy to recognize.

Two species of shrikes inhabit the U.S. and Canada. The northern shrike breeds in Alaska and northern Canada and sometimes ventures this far south during the winter. In fact, I had one reliable local report of a northern shrike this winter. The loggerhead shrike -- so named for its big head -- nests across most of the U.S and winters in the southern tier states. Its numbers in recent years are declining for reasons unknown.

One year, after seeing a shrike, I told my ornithology class to inspect the fence it had been perched upon. "Can you find anything unusual," I asked. In just a few minutes they called me over and showed me a small lizard impaled on a barb.

"Is this what we're looking for?" one asked. It was. Shrikes are predatory songbirds. Not only do they eat grasshoppers and other insects, they also eat vertebrates -- small birds, mice, frogs, snakes and lizards. And they have the curious habit of impaling their prey on large thorns of locusts, other thorny trees and barbed wire. This behavior has earned them a not so flattering nickname: "butcherbird."

Shrikes, like blue jays and some woodpeckers, cache food for later use. But shrikes impale their prey on thorns instead of hiding it. They use a thorn as an anchor to hold down the victim while they kill it with their powerful beak.

Impaled prey also serves another purpose, at least in some areas. Ornithologist Sarah Sloane reports an alternative explanation for shrikes impaling their prey. She studied a population of shrikes in Florida and noticed that often shrikes did not return to impaled prey items. So why kill them in the first place?

Sloane conducted some field experiments to find some answers. She found a stretch of barbed wire upon which 28 prey items were impaled -- crickets, grasshoppers and lizards. She removed all 28. Two days later 26 new victims decorated the wire. Certainly more than an individual bird would require that much food.

In further tests she found that 48 percent of all impaled items remained untouched. And when shrikes impaled prey on thorns of trees, they selected thorns on the outer, most conspicuous branches rather than harder-to-see inner branches.

Sloane concluded that shrikes, at least those she observed in Florida, impale prey to advertise their presence. Impaled prey supplements male song as a way to identify territorial boundaries and attract females. A fence full of prey suggests a strong, capable shrike lives nearby.

This does not mean that shrikes never return to cached prey or that they don't ever use thorns to help manipulate large prey. It merely suggests that in the South, where small prey items are abundant, impaling prey serves an additional function.