Migrants intrude; scarce pronghorn die

CABEZA PRIETA NATIONAL WILDLIFE REFUGE - Biologists working on this remote stretch of desert in western Arizona have noticed a troubling spike in migrant traffic since early spring. It's gone from a handful of crossers a night to 200.

Biologists here have never seen numbers that high, and they worry it could have deadly consequences, both for the migrants and for the Sonoran pronghorn, one of the most endangered animals in the world.

While Cabeza Prieta shares a 60-mile border with Mexico, the increased migration has been funneled though a single, narrow valley. It's the same area where biologists and volunteers have been installing watering holes and irrigation plots to bolster the native plants that pronghorn graze on as their main source of food and water....

Of the five types of pronghorn in the United States, only the Sonoran can survive the harsh Arizona desert....

"You cannot take an animal from Wyoming and drop it down here in the Sonoran Desert and do anything but watch it die," said Mike Coffeen, wildlife biologist for Cabeza Prieta.

Today, only 58 adult Sonoran pronghorn survive in the United States. They've been on the endangered species list since the list was created in the mid-1960s....

Today, their fiercest predators are drought and human activity. Historically, the animals could travel from the Colorado and Gila rivers to the Gulf of California to look for water. But highways, railroads and canals have cut off traditional water sources, and as fast as they run, pronghorn will not step on a paved road. Biologists have seen them die of thirst rather than cross a highway.

About 600 Sonoran pronghorn live in Mexico just south of the refuge. Ten years ago, the Arizona herd had about 250 animals. A drought in 1994 reduced their numbers to about 140. Then, in 2002, a devastating drought hit....By the time it rained in September, only 19 animals remained alive.

...nobody imagined migrant traffic would shift so dramatically in this direction.

Coffeen attributed the shift to recently installed vehicle barriers through neighboring Organ Pipe Cactus National Monument. It's tougher to go through Organ Pipe, so people go around, onto Cabeza Prieta, he said....

Desert Invasion - U.S.

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