On a 90-degree day in early June, Rob Roy Ramey II hikes up a steep ridge in Boulder Canyon toward a spot overlooking a golden eagle’s nest. The conservation biologist has volunteered to keep tabs on a hatchling for the Colorado Division of Wildlife.

A compact man with sapphire eyes and a tanned face, Ramey thrives on fieldwork. "I’ve risked my life for endangered species," he says. He’s shot tranquilizer darts at elephants in Zimbabwe, led posses of bewildered locals on harebrained plots to herd Argali sheep in Mongolia, and nearly crashed in a helicopter while studying bighorn sheep in Death Valley.

As he walks, Ramey pontificates — about the importance of getting out into the wild, his critics, and the problems he sees with the Endangered Species Act. At times, his brain seems to spit out ideas faster than his tongue, or lungs, can keep up. Halfway up the climb he stops, not from fatigue, but because he needs to catch his breath after making an especially emphatic point.

At the top of the ridge, Ramey pulls a spotting scope from his well-worn backpack and focuses the viewfinder on the eagle’s nest. "Oh, look! Mom’s feeding junior," he says.

Glassing the eaglet, Ramey acts like a father watching his child’s first steps. But Ramey is careful not to fall into the role of an overly protective parent, and that resistance has won him few friends in the environmental community.

Just up the canyon from here lies Security Risk Crag, one of several rock-climbing areas the U.S. Forest Service’s Boulder Ranger District closes off each spring to protect eagles’ nests. Ramey supports the policy, but when climbers questioned whether the nest at Security Risk was in fact used by eagles, he responded with the mantra that has guided his career: "Show me the data."

Ramey rappelled into the nest and analyzed its contents. He found no evidence that eagles had ever laid eggs in the nest — he suspects it’s used by ravens — and he backed a movement to keep the crag open year-round. So far, the District’s policy hasn’t changed, but Ramey’s actions earned him scorn from some Boulder environmentalists. "Some people didn’t want to accept the facts," he sighs.

The eagle hullabaloo symbolizes the larger criticisms Ramey has lobbed at the U.S. Fish and Wildlife Service’s efforts to protect threatened species. Too often, he says, conservation decisions are based on hypothetical threats or overly cautious assumptions, rather than hard facts.

As evidence, Ramey points to the Preble’s meadow jumping mouse, a creature found only in streamside areas along Colorado’s Front Range. The 3-inch-long mouse has powerful, elongated back legs and clown-sized hind feet that can propel it three feet in a single hop. To evade predators, the mouse can jump like a kangaroo, up to 18 inches high, using its 6-inch-long, whip-like tail as a rudder to switch directions in mid-air. But the little acrobat’s most famous feat is its leap onto the Endangered Species list, a move that has hindered the march of bulldozers along the base of the Rocky Mountains.

One of 12 subspecies of meadow jumping mouse (Zapus hudsonius), the Preble’s mouse was first described in Colorado by naturalist Edward A. Preble in 1899. Nearly a century later, in May 1998, the U.S. Fish and Wildlife Service listed the mouse as threatened and designated 31,222 acres of critical habitat. The listing placed new restrictions on development in moist meadows and streamside areas from Colorado Springs to Laramie, raising the ire of developers and some residents, who complained that, in the words of one letter-writer, the government was putting a disease-carrying rodent ahead of the rights of landowners. Meanwhile, environmentalists rejoiced: The little mouse had given them a new weapon in their drive to limit development in Colorado’s growing metro areas.

Enter Ramey, who, in 2002, got to digging through the scientific literature after a colleague suggested they collaborate on a Preble’s mouse project. Ramey found that the 1954 monograph that classified the Preble’s mouse as a distinct subspecies, had — like many such distinctions of its day — been based almost entirely on the critter’s physical characteristics. Philip Krutzsch, a professor emeritus at the University of Arizona, had made the designation based on coat color and skull measurements – and he’d done so using just a handful of mice. "He’d only looked at four adults and seven juvenile specimens. Juveniles have tons of variation in their coat color," says Ramey, who at the time worked at the Denver Museum of Nature and Science.

With so few specimens, it was possible that the differences Krutzsch had used to split the Preble’s mouse into a new subspecies were just an artifact of his small sample size. "I said, ‘Aha! This is the question to ask: Is this mouse really distinct?’ " says Ramey.

What happened next threw Ramey smack into the middle of one of the Endangered Species Act’s ugliest quagmires. On the surface, it looks like a simple dispute between "lumpers" — biologists who pack varying plants or animals into a single species or subspecies — and "splitters" — those who see such variations as reason to divide wildlife into different classifications. But the debate runs much deeper than science, touching on issues that involve philosophy as much as science. One central question: As long as the government possesses only limited funds to float an endangered species ark, how should it decide which passengers to allow onboard?