CHARLESTON, W.Va. -- What a difference a thousand miles can make.
Along the U.S.-Canada border, people and wildlife pass relatively freely. Most wildlife crossings go unnoticed. Wolves, bears and moose have no need for borders.
But every few years a visitor from the north captures the birding world's attention. Snowy owls, residents of the arctic tundra, have been reported in Pennsylvania and Ohio this winter. Just a few weeks ago I read that at least 400 were known to have reached Wisconsin. Popularized by the Harry Potter movies, snowy owls are large and conspicuous. They wander south when lemming populations crash.
Lemmings are small, mouselike rodents and an important food item for snowy owls. Though lemming populations crash every four years, snowy owls visit unpredictably. They eat other prey, too, such as snowshoe hares, grouse, songbirds and small ducks, so they are not tied exclusively to lemming populations.
In fact, when lemming numbers boom, so too does snowy owl nest success. But when lemming populations inevitably crash, competition for food intensifies for the now larger owl population. Older owls usually hold their ground; younger individuals face a choice: Move south or starve. At least that's one interpretation of the facts.
Fortunately, there's an easy way to age snowy owls in the field. Snowy owls stand almost 2 feet tall, have a 4-foot wingspan and bright yellow eyes. Adult males are mostly white, and adult females show some black barring. But first-year birds are heavily marked by black horizontal bars. They appear noticeably darker than adults.
So keep binoculars in the car, and check out any large, pale, "earless" owls you might see perched on fence posts, and buildings near hayfields, grasslands and airports. If the birds are mostly white, they are probably adult snowy owls. If they seem dirty or the black barring is evident, they are juveniles.
Along the U.S.-Mexico border, it's a different story. Walls and fences stretch intermittently along the nearly 2,000-mile international border to keep illegal immigrants out of the U.S. Based on news reports, they are not terribly effective. Long, sophisticated tunnels seem easy to build. And a 2009 government report revealed that there had been 3,363 breaches of the fence just through May of that year.