As Fences Cut Off Migration, Hoofed Species Decline

A Dama gazelle at the Smithsonian’s National Zoo. i i

Dama gazelles were once common in the grasslands and subdesert of the Sahel in Africa. They used to migrate south in search of food during the dry season and return north after the rains came. Poaching and destruction of their habitat have greatly diminished their numbers, and today there may be just hundreds left in the wild. Mehgan Murphy/Courtesy Smithsonian’s National Zoo hide caption

itoggle caption Mehgan Murphy/Courtesy Smithsonian’s National Zoo
A Dama gazelle at the Smithsonian’s National Zoo.

Dama gazelles were once common in the grasslands and subdesert of the Sahel in Africa. They used to migrate south in search of food during the dry season and return north after the rains came. Poaching and destruction of their habitat have greatly diminished their numbers, and today there may be just hundreds left in the wild.

Mehgan Murphy/Courtesy Smithsonian’s National Zoo
A herd of elk on the prairie. i i

Elk migrations are a tiny fraction of what they used to be, says Joel Berger of the Wildlife Conservation Society. iStockphoto.com hide caption

itoggle caption iStockphoto.com
A herd of elk on the prairie.

Elk migrations are a tiny fraction of what they used to be, says Joel Berger of the Wildlife Conservation Society.

iStockphoto.com

One of the most spectacular events in nature — mass migrations by large, hoofed, grass-eating animals — is endangered. That's what scientists conclude after completing what they say is the first comprehensive look at this phenomenon.

Grant Harris from the U.S. Fish and Wildlife Service and a team of scientists compiled a record of all the great migrations in the historical record. These are "charismatic megafauna," says Harris: wildebeests and oryxes in Africa, caribous in North America, the antelopelike chiru in Asia. They move by the thousands over hundreds of miles of territory, seeking out fresh grass or other forage or water. In some northern areas, they migrate to escape deep snow. Often they mate during migrations. The animals also influence the landscape by eating certain plant species, effectively changing the mix of vegetation in the regions they pass through. And, their feces fertilize the vegetation.

Migrations Decline Across The Globe

The researchers concluded that there have been 24 big migrations around the world.

"Of those 24," says Harris, writing in the journal Endangered Species Research this month, "we've lost six species that do not migrate in large masses, in long distances, anymore."

The remaining 18 large migrations are endangered, says biologist Joel Berger of the Wildlife Conservation Society, who collaborated on the study.

"Pronghorn migrations are a sliver of what they used to be," he says. "Elk migrations are a sliver of what they used to be. So I think our 25 percent glimpse globally is probably a huge underestimate" of the lost migrations.

Some of the animals that once migrated are extinct, say Harris and Berger, such as the quagga, an African zebra. Others, like the scimitar-horned oryx, are extinct in the wild and kept from total extinction in zoos. Fences and modern agriculture have blocked migrations. Hunting has killed off large numbers as well. Roads and urban development have diverted others.

Wildlife Corridors Could Help Herds

Scientists missed what was happening as these migrations dwindled or disappeared, says Steven Montfort, a wildlife biologist who runs the National Zoo in Washington D.C. Keeping some of these animals in parks is only a stopgap measure.

"If you fenced in scimitar horned oryx," Montfort says, "and I don't care how big of a fenced area, you can think of the largest fenced area ever invented, there's a chance that the rain and the grasslands are going to fall outside the fenced area. They are going to go right to the fence line and they are going to starve to death."

One solution is to create wildlife corridors, even only a mile wide, that allow migrating animals to move unhindered between grazing areas. But ultimately, say these scientists, migration itself won't survive without big, unfenced places left to the animals.

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