BIG BEND NATIONAL PARK, Texas — The yellow diamond-shaped signs posted along the twisting road leading to the Chisos Mountains serve as a warning.
But the blackened image in the middle is not of a deer, nor of pedestrians.
It is a bear.
To the delight of wildlife scientists and animal lovers, the black bear has returned to Big Bend National Park and reestablished a population after a 50-year absence caused by hunting.
"It's probably the most exciting thing since the park's existence," said Raymond Skiles, a wildlife biologist with the National Park Service.
Now park officials want to do everything they can to preserve the population, currently estimated at 20 bears.
That means two things: keeping humans and their food away from the creatures, and studying the bears to learn where specifically they are living, their travel routes and whether they are inbreeding.
Big Bend officials have picked up a trick or two from their counterparts who have been dealing with black bears at other national parks for decades. At least 600,000 black bears are believed to be in North America today, with more in Alaska than any other state.
Workers have installed bear-proof trash cans with secure metal lids and food-storage lockers at campsites and along hiking trails in the 15,000-acre Chisos Mountains, the new habitat for a group of bears believed to have migrated from the Sierra del Carmen, a mountain range just across the border in Mexico.
What's more, they have put placards on the tables in the park's only dining room reminding visitors to keep food in cars and lockers, not tents and coolers.
Park officials hope such measures will avert the types of problems experienced at some other parks, where hungry bears have ripped off car doors.
"Big Bend is lucky in that they can start at the outset, taking advantage of these techniques that other parks have developed to try to head off nuisance activity," said Mike Pelton, an expert on black bears and a professor of wildlife science at the University of Tennessee.
In the early part of the century, black bears inhabited the land in southwestern Texas that is now Big Bend but were lost to hunting and trapping by the time the park opened on 800,000 acres in 1944.
It wasn't until the mid-1980s that people started seeing black bears in the park's rugged, reddish-brown mountains, wandering among the drooping junipers and oaks and snacking on the purple fruit of the prickly pear cactus.
Then, in 1988, a visitor captured snapshots of a mother bear and three cubs--the first evidence of a breeding population.
As the black bear population blooms across the country, more people are becoming aware that the bear--often perceived as a ferocious beast--is timid and extremely unlikely to attack a person if left alone.
Only about 40 people have been killed by black bears in North America this century, said Lynn Rogers, a director of the North American Bear Center in Minnesota and a retired wildlife biologist for the U.S. Forest Service.
"People are learning the truth about these bears and are willing to coexist with them," Rogers said.
Bears subsist on a mostly vegetarian diet of nuts and berries but will eat meat that is easily obtained. Problems arise if they get a taste of human food: There have been many cases around the country in which bears searching for food have broken into houses, ripped tents and mauled people. Many pesky bears have had to be shot.
So far in Big Bend, which welcomes an average of 300,000 visitors a year, no problems have been reported between the new bear population and park visitors.
Besides hiding food from the bears, Big Bend's preservation program has another important component: the three-year study being conducted by researcher Dave Onorato, a doctoral student from Oklahoma State University.
Using techniques that are not uncommon for studying black bears, Onorato is trapping and holding the animals just long enough to draw blood, take ear tissue and hair and pull a tooth. And, using a needle, he injects a three-quarter-inch device between the scapulae that gives each bear an individual code, which can be read with a scanner.
All this poking and prodding is done to determine the number of bears, their ages and whether they are inbreeding, which could lead to sterile males. If that turns out to be the case, park officials may have to import some black bears to diversify the population.
"In order to preserve these bears, it's important that we know more about them," Onorato said.
Before he finishes with a tranquilized bear, Onorato attaches an electronic collar so that he can track its movements with a scanner. So far, he's taken samples from and put collars on 12 bears.
By mapping the bears' movements, Onorato will learn how they are traveling and how close they are coming to campsites and popular tourist areas.
"If the park wants to avoid problems, we need to determine where the bears are spending time," he said.
Skiles said he and other park officials hope to use the data "to literally manage the people around the bears."
"Ultimately," he said, "we just want to preserve this population and want it to do what it naturally would."