The next year, Woodbridge and two colleagues traveled to the hawks' wintering ground in Argentina to try to find out why so many were disappearing. They were astonished. Back in California's Butte Valley, he'd spotted the hawks only occasionally, but in Argentina he discovered huge flocks -- sometimes thousands of hawks -- roosting in non-native eucalyptus groves called montes. And something was obviously very wrong: As he drove to a ranch to find the hawk he'd outfitted with the transmitter, he passed hundreds of dead birds on the ground. Woodbridge found that the farmers there had started using a deadly pesticide called monocrotophos. Hawks were drawn to spraying operations to gobble up squirming, dying grasshoppers and ingesting toxic amounts of the pesticide. Some died with grasshoppers in their talons, having absorbed the poison through their feet. In some cases, a fifth of the birds that roosted in a given monte were killed.

Woodbridge's pioneering research with satellite telemetry led to the formation of the International Swainson Hawk Working Group, which met with Argentine farmers and pesticide manufacturers, who eventually agreed to phase out toxic pesticides. "Satellite receivers were transformative," Woodbridge told me.

I had the same thought in 2005, when -- under the glow of four headlamps in Glacier National Park -- I watched as four biologists unwrapped the down coat covering an anesthetized wolverine and swabbed its belly in preparation for surgery. It was a typical combination of old and new technology: They had captured the wolverine in a hand-hewn log trap that snapped shut when the animal yanked on a piece of meat. When Jeff Copeland, the head of that U.S. Forest Service research project, approached the captive wolverine -- dryly named "M-1" -- it snarled and growled, and as he carefully opened the trap's lid to peek in, it lunged at him, taking a chunk out of the log near his hand. Copeland gingerly used a jab stick with a hypodermic at the end to sedate the wolverine and, after it fell asleep, picked it up and brought it to the table, where they operated. The biologists carefully sliced open the wolverine's belly and implanted a tiny satellite transmitter under the skin.

They wanted to find out where wolverines go in the forest, and how much snowmobiles and other winter recreation are invading the species' winter redoubts, and whether the Endangered Species Act should require protection of the habitat. Once the wolverine was released, they tracked it every two hours, using satellites, watching as it crossed 25 miles of a snow-covered mountain range in one day, and 25 miles the next. Wolverines are rare and secretive animals, so no one knew about their wide-ranging nature until some were successfully collared and tracked. Now the discussion of whether that species and its surprisingly large habitat need legal protection can incorporate the researchers' findings, including the fact that a male wolverine's home range spans 500 square miles. As Copeland said, "The hallmark of the wolverine is its insatiable need to keep moving."

In 2008, I visited a concrete underpass on Interstate 90 in the mountains west of Missoula, Mont., with Chris Servheen, a U.S. Fish and Wildlife Service biologist who's a long-time leader in the effort to protect and increase grizzly bear populations. As we walked the dirt and gravel between gray pillars and under a massive gray roof, with tractor trailers and cars whizzing overhead, Servheen pointed out the heat- and motion-activated cameras mounted in various places.

Hundreds of grizzly bears roam the mountains north of the highway, in the Northern Continental Divide Ecosystem, which includes Glacier National Park. But almost none have been spotted to the south, in good habitat whose core is the sprawling Selway-Bitterroot Wilderness. In the 1990s, biologists proposed moving bears into the Selway-Bitterroot, but Congress, reacting to the anxieties of some locals, forbade it. Now biologists are hoping grizzlies will move there on their own, but I-90, with six lanes of high-speed traffic and several rows of concrete jersey barriers, remains an obstacle. The bears seem to refuse to use the underpass. A few years into this monitoring project, the cameras in the underpass have snapped pictures of deer and a host of other critters, including ATV riders, but no grizzlies.

Servheen's career, like mine, has spanned the evolution of the new technology. He remembers how the old-style radio collars required biologists to go airborne just to discover "where a bear was twice a week, during good weather, at 10 a.m.," he said, adding wryly, "If you know where I was at 10 o'clock in the morning twice a week, and you tried to draw conclusions about the places I like to go in my weekly activities, you would be pretty limited."

In contrast, the modern collars can find a bear 24 hours a day with an astonishing degree of accuracy, pinpointing an animal within 10 yards of its actual location. Sometimes biologists still go airborne to gather data, but as they fly over a bear, the collar is "interrogated" by an onboard computer, the data is beamed skyward and, in a few seconds, the entire trove is downloaded remotely into a portable laptop. Some modern collars contain a bolt-shearing mechanism set to go off at a predetermined time, reducing stress on both the bear and the biologists who retrieve its collar. "The bear stands there, there's a little pop and it falls off its neck," Servheen said.

The modern collars report in great detail where grizzly bears travel over periods as long as two years, exposing their behavior far more accurately than a TV "reality show" would. We've learned that the huge bears come surprisingly close to people's homes at night, moving so surreptitiously that the residents don't see them. That warns managers when to ask people to remove bird feeders and other bear attractants.

"The technology gives us a much better and more profound understanding of how bears respond to human activity on the landscape, and how we can better manage that human activity," said Servheen. "We can identify the places where bears cross the highway, so if a group like The Nature Conservancy wants to put in a conservation easement to protect a crossing, we know exactly where that is and can get the biggest bang for the buck." Even so, we still don't know for sure why grizzlies refuse to use that I-90 underpass.

Kate Kendall, a research ecologist with the U.S. Geological Survey, based in West Glacier, Mont., has created her own special recipe for grizzly bear soup: She dumps assorted carp, trout and other fish into a 55-gallon drum, and stirs in cattle blood gathered from slaughterhouses. Then she seals the fetid concoction and lets it age for a year, until it's good and ripe. "Then we open the drums and bottle it," she told me recently.

Last summer, Kendall and 75 others on her crew wrapped barbed wire around stands of pine trees at 395 locations in northwestern Montana's two-and-a-quarter-million-acre Cabinet-Yaak Ecosystem, to create what she calls "hair corrals." In the center of each corral, the team placed a generous dollop of Kendall's homemade lure on a pile of brush and stumps.

Remote cameras show that after the team left each corral, it seldom took long for the scent to work its magic. As the bears sneak under the wire to check out the heavenly smell, the barbs snag clumps of their hair. That project snagged 17,000 hair samples in that ecosystem. Once black bear hair is excluded from the samples, the DNA -- the basic genetic material -- in each grizzly hair will be assayed. In 2014, for the first time ever, the local people will have a realistic idea of how many grizzly bears live in the Cabinet-Yaak ecosystem, where they go and even their kinship: which bears are related to others and in what ways. That will give bear managers a much better sense of how many animals they are dealing with, compared to previous estimates based on radio collars and sightings. Moreover, the bears will never see a human being, never be drugged, and probably never know they have been studied.