"If people care about spectacular processes that once crossed vast landscapes, we've got to be creative and do things now," Joel Berger, wildlife biologist for the Wildlife Conservation Society, told United Press International. "Otherwise, no one is going to see long distance migrations outside of the Arctic."
Many of the last, large migrating herds are located in and around Yellowstone National Park. In a paper in the April issue of the journal Conservation Biology, Berger found 78 percent of the pronghorn antelope and 58 percent of the elk migration routes there have been curtailed. Bison no longer migrate at all from Yellowstone.
North American herd migrations once were nearly on the scale of the better-known migrations of African wildlife. Kob, chiru, wildebeest and gazelle all migrate from between 300 miles to 500 miles roundtrip annually. In North America, pronghorn from Yellowstone still migrate an estimated 300 miles roundtrip.
"In areas of low human density in the Western Hemisphere," Berger wrote, "five social and non-gregarious species, all from the same region of the Rocky Mountains, still experience the most accentuated of remaining New World, long-distance migrations south of central Canada." The five are bison, pronghorn, elk, moose and mule deer.
"These movements occur in or adjacent to the Greater Yellowstone region," Berger continued, "where about 75 percent of the migration routes for elk, bison and North America's sole surviving endemic ungulate (the pronghorn) have already been lost." Moose and mule deer migrations have not been curtailed, however, he added.
The example of this trend that stands in boldest relief is the American bison.
Perhaps 40 million buffalo -- experts disagree on more precise estimates -- once roamed the American West. Wildlife biologists were not available to tag individual bison with radio collars, so evidence about their migrations is only anecdotal. However, they apparently did roundtrips of nearly 400 miles every year.
By the beginning of the 20th century, the American buffalo had become nearly exterminated. At the time, more bison lived in the Bronx Zoo than in Yellowstone. There were fewer than 1,000 left anywhere in the wild.
Thanks to the efforts of Bronx Zoo director William Hornaday, the animal was restored to many places in the West -- including Yellowstone. But those spectacular migrations are gone. The bison's route has been cut off entirely. Those that attempt to follow their ancient instincts to wander from the park are shot, to prevent them from spreading brucellosis to cattle.
Pronghorn remain the lone, long-distance migratory species as they move southward from Yellowstone and back more than 300 miles, as they have done for at least the last 5,800 years. But even this transit must pass through a narrow bottleneck in Wyoming's Upper Green River Basin known as Trapper's Point. It is less than a mile wide, is a major oil and gas development area and holds two home developments that constrict the migration route even further.
Berger, along with other conservationists, has proposed the creation of national migration corridors to keep these traditional routes open -- at least for the antelope that have to navigate Trapper's Point. At one stretch in the Bridger-Teton National Forest, the antelope must march single-file. In another, they have to use a highway underpass.
"The number of oil and gas wells going in is so phenomenal that it is altering an area that was a natural environment and turning it into an industrial landscape," the Sierra Club's Kirk Koepsel told UPI.
Of the proposed migration corridors, Koepsel said, "It's an accepted practice that doesn't happen very often. More and more people are looking at it as a way of dealing with development."
The impact on the animals from this loss of migration habitat seems to vary. Bison, which have not been able to migrate from Yellowstone for generations, appear to have, figuratively, shrugged their shoulders and gotten on with life -- they are thriving within the confines of the park, even if they cannot leave it.
"Bison are big, they don't have any worries," Berger commented. "They don't have specialized habitat needs."
Pronghorn, which in the northern portion of the park have seen their migration routes entirely cut off, are another story, he said. They have shown poor fawn survival and declining populations, at least for the last 10 years, to the point where park officials have expressed concern about localized extinction.
"For the the Upper Green River Basin," Berger wrote in the conclusion of his paper, "the designating of a formally protected corridor ... would represent a landmark victory nationally and internationally because (it would) bring an ecological process, long-distance migration, to the attention of the public. As such, this proposal could sustain a macroscale phenomenon not repeated in grandeur between Tierra del Fuego and central Canada."
Dan Whipple covers the environment for UPI Science News. E-mail firstname.lastname@example.org