updated Dec. 30, 3011

Every May for the past five years, Jackson Hole, Wyo., has celebrated the return of 300 or so Antilocapra americana to nearby Grand Teton National Park. The revelry is not just to honor the animals for completing their remarkable 120-mile-long seasonal migration. It also salutes a Herculean communal effort: the 2008 signing of a forest plan amendment establishing federal protection of "The Path of the Pronghorn," the 45-mile portion of the migration that traverses U.S. Forest Service land.

The pronghorn travel from Grand Teton to the Upper Green Valley, in search of respite from heavy snows that hamper winter foraging. Along the way, they cross paths with powerful interests -- namely, one of the most significant natural-gas developments in recent years. In the late 1990s, "fracking" technology, combined with 3-D seismic surveys, enabled a mind-boggling increase in the extraction of natural gas from the area. In 1994, 40 gas wells were approved for drilling in the Jonah Field; by 2006, there were 3,100. In 2008, 4,399 additional wells were approved at the nearby Pinedale Anticline Project. The pace has slowed during the economic downturn, but development continues.

In the early 2000s, two prominent biologists with the Wildlife Conservation Society, Joel and Kim Berger, observed that the proliferating development associated with drilling was making it harder for pronghorn to move freely, potentially preventing them from completing their migration. The Bergers spearheaded biological studies and public outreach, and Kniffy Hamilton, who was then supervisor of Bridger-Teton National Forest, worked to safeguard the portions of the migration route that fall under agency jurisdiction. Along the Path of the Pronghorn, which narrows to about a half-mile wide in many places, aboveground drilling facilities are now prohibited, though subsurface drilling is still allowed.

The Wyoming Department of Transportation is building two wildlife highway overpasses on the migration route south of the protected corridor, and volunteers and conservation groups have cleared away unnecessary fences and redesigned hundreds of miles of other fences on national forest and private land so that pronghorn can crawl underneath them. Together, these efforts have kept an important wildlife migration route alive. But despite its success, the Path of the Pronghorn remains the only official national migration corridor in the United States.

We congratulate ourselves for protecting places like Grand Teton National Park. But putting an artificial boundary around a natural area does not adequately protect its inhabitants. Absent connection with one another, ecosystems are doomed to unravel: Isolation leads to inbreeding within individual populations, and disrupts key relationships among species. After wolves were extirpated from Yellowstone National Park, newly unafraid elk chowed down aspen stands crucial to beavers, and the beaver followed the wolf out of the ecosystem. Ever since wolves were reintroduced, the park's beaver population has steadily increased, and various bird and fish species have begun to recover.

Yet wildlife corridors are difficult to define, much less legislate. Animals like pronghorn, which have a clear and traceable movement pattern, are lucky -- it's relatively easy to mark out the territory they need and safeguard it. But all of nature essentially relies on movement of one sort or another, and most of those movements are far less disciplined. A pronghorn corridor is substantially different than a migration route used by a wolverine, or a frog, or a migrating bird or butterfly. Depending on the location and the species in question, a corridor can be anything from an enormous swath of undeveloped land to a strategically placed line of fencing.

One way to identify multi-purpose wildlife corridors is to target an "umbrella" species, a large carnivore, for example, hoping that protecting its wide range will protect other species as well.  The Path of the Pronghorn does not quite fall into this category, because only a very narrow stretch of land is protected; on the other hand, some of that land does provide habitat for other species that the state of Wyoming considers to be among its "75 Species of Greatest Conservation Need."

Some scientists are skeptical about the benefits of protected wildlife corridors, saying that animals may not use them as intended and fearing that the linkages might encourage the spread of invasive species. But a recent review of 78 experiments from 35 studies found that protected corridors increase movement between habitat patches by about 50 percent. On the wildlife overpasses and underpasses that connect habitat divided by the Trans-Canada Highway in Banff, researcher Tony Clevinger documented more than 200,000 individual animal crossings by elk, moose, wolves, bears and other species over a 14-year period.

Paul Beier, a professor in the School of Forestry at Northern Arizona University, has perhaps designed and helped implement more wildlife corridor protections than anyone else. While corridors do promote animal movement, he says, the main challenge is designing and managing them -- making sure they are broad enough, and protected enough, to support animal movement. Accomplishing that is not a scientific problem, but a political one.