In answer to the ages-old question, the bear crossed the road to get away from his parents. He was no chicken.

Like adolescents of many species, this young male black bear had a powerful urge to leave home. His mother’s growing hostility, his father’s intolerant rule over surrounding territory and his own instinct to explore propelled him out into an unfamiliar world.

He was searching for a new home range, someplace far enough away where he could find females not claimed by his father.

But crossing unknown ground is the most dangerous thing any young, inexperienced animal can do. It meant the death of this bear when a car hit him one night on a rural highway near my house in the mountains of Virginia.

I could surmise this story from the shaggy little body on the roadside because of a phenomenon wildlife biologists call “dispersal of young.” It’s a fundamental process that inhibits inbreeding and maintains genetically healthy populations.

Timeless patterns of seasonal migration also prompt many species to travel.

Salamanders, frogs and toads emerge from winter homes during spring thaw and move to small ponds to mate and lay eggs.

Generations of monarch butterflies flutter from wintering sites in Mexico to Canada and back again.
Twice every year, migratory songbirds journey across continents. Theoretically, birds can fly over hostile terrain, but in reality they need to touch down often to find protected places to rest and feed.

Even animals that don’t migrate must travel to reach the different foods available in different seasons. If water, food and nesting sites are scattered across the landscape, the animals most common to our landscapes, like raccoons, opossums, skunks, groundhogs, squirrels, chipmunks and even mice, may have to cross roads daily.

Without safe travel routes, they are all at great and increasing risk.

The four million miles of road that craze this country like cracks in an old porcelain plate fracture the populations of many wildlife species. The Humane Society of the United States estimated in the 1960s that one million vertebrate animals were killed on our roads every single day of the year. That number surely has grown.

The numbers of invertebrate dead — butterflies, bees, worms — are uncountable. The toll goes ever higher as more roads are bulldozed across habitat.

More insidious than the direct deaths roads cause, and even more devastating in the long-term, is the isolation that roads enforce on both animal and plant populations.

By rendering it deadly for animals to cross — and, with them, the pollen or seeds that generate new plants — roads become an ever-tightening noose as inbreeding weakens populations.

Wildlife travel corridors are one good solution. First proposed by Harvard biologist E. O. Wilson three decades ago, they are strips of natural vegetation (often along streams) that link patches of natural habitat otherwise surrounded by human development.

At first, skeptics argued that corridors could be more dangerous than beneficial by also offering travel routes for diseases and invasive species. Decades of scientific research clearly refute that position. The benefits of corridors heavily outweigh any disadvantages.

Essential to the effectiveness of corridors are road crossings made safe for wildlife.

An early example of wildlife crossings was the upgrading of State Route 84 to Interstate 75 through the heart of the endangered Florida panther’s habitat. Fencing was installed along the widened road to guide panthers to underpasses placed where the animals were known to cross.

Deer, bobcats, raccoons, alligators, black bears and panthers have been photographed using the underpasses.
Also successful are the tunnels beneath a road in Amherst, MA, that allow spotted salamanders to reach their traditional breeding ponds.

Near Banff National Park in Canada, fencing and underpasses were installed during a major road’s reconstruction. The result has been a 96 percent reduction in elk and deer roadkill.

Lessons from these examples should be applied to the planned widening of Interstate 81 through western Virginia. This interstate, which runs down the middle of the Shenandoah Valley, already nearly severs the Blue Ridge from the Allegheny Mountains in terms of animal travel. Adding even more lanes will virtually guarantee the isolation of many animal populations that normally exchange members across the two ranges.

Corridors would increase human safety, too. Several hundred Americans are killed every year in vehicular collisions with deer, and damage runs into the hundreds of millions of dollars. The man who hit the bear had a badly crumpled fender but was grateful it wasn’t worse.

Building wildlife corridors into our road systems should be considered an integral part of the cost of doing business — not just for big animals, and not just for human safety.

Our fellow travelers on this planet have their own paths to follow. Let’s help make sure their journey is a safe one.