YOSEMITE NATIONAL PARK -- High above a silver-blue mountain lake, a gray-bearded man tromped up a rocky slope and peered at a small metal trap. It was empty.
He kept moving, scrambling across huge granite boulders and found another trap. This time, success: "We got something," he said.
Jim Patton, a retired professor of zoology at the University of California at Berkeley, had his quarry: the tiny, ash-gray alpine chipmunk, a Sierra Nevada native that is one of the leading sentinels -- and apparent victims -- of climate change in the United States.
One century ago, alpine chipmunks owned the upper half of Yosemite. They skittered under logs and darted across rocks from the rugged Sierra crest down to the conifer forests at 7,800 feet. Today, they are missing in action lower than 9,800 feet.
"It's lost half its geographic range," Patton said. "Climate is the culprit. I don't think there is any iota of reason not to think that."
Tipping the boxlike trap, Patton shook it and one very frightened chipmunk tumbled into a white sack. Patton gently snipped a piece of flesh from its ear for a DNA sample -- and released it. Next, he pulled out a notebook and wrote the elevation: 10,020 feet. Seven hundred feet overhead, the slope he was working on yielded to blue sky.
"Eventually, it's going to get shoved off these mountains and go extinct," Patton said.
For years, climate change was a story told largely via melting snow and ice. Now, species and ecosystems are feeling the heat, too. Butterflies are expanding their ranges northward. Migratory birds are arriving earlier in the spring. And here in the Sierra and in other mountain ranges around the world, species not considered migratory -- from stately conifers to diminutive chipmunks -- are on the move, creeping up toward cooler, more hospitable abodes.
Along with that movement comes stress and danger. Ultimately, national parks such as Yosemite could lose significant portions of their mammal species as habitats unravel because of climate warming from the buildup of greenhouse gases, according to a 2003 paper published by the National Academy of Sciences.
"Animals that can fly are in pretty good shape," said David Graber, chief scientist for the National Park Service in California. "Animals that are relatively static have a much more limited ability to move. If climate changes faster than they can find new habitat, they're out of business."
About the size of your cell phone, the alpine chipmunk may not be a well-known symbol of climate change. It's hard to compete, after all, with a 600-pound polar bear stranded on melting slabs of sea ice. But the drama unfolding here along the roof beam of the Sierra is just as poignant and populated by a cast of unsung creatures -- from ground squirrels to wood rats -- that are at risk, as well.
It is a story that might have remained untold if not for the pioneering work of Joseph Grinnell, the founding director of UC Berkeley's Museum of Vertebrate Zoology who directed the first in-depth survey of Yosemite's wildlife almost a century ago.
An eye for detail
Seeking specimens for his new museum, Grinnell set out across the park with a team of assistants for one of his expeditions in the summer of 1915. They trapped ground squirrels, shot songbirds and even bagged a wolverine. But unlike other collectors, they took elaborate notes on everything -- whether they captured it. Grinnell was the note taker in chief.
"We'd be sitting in camp and we'd both be skinning. Pretty soon, he'd throw a rat over to me and he'd say: 'Here, Russell, finish this one up,' and he'd just ... pick up his notebook and start writing," one colleague, Ward Russell, said about Grinnell in an interview with a UC Berkeley professor in 1992 (listen to it online at www.sacbee.com/links).
"We never traveled one inch but what he had that notebook open and writing notes," Russell said. "He said over and over: 'Put it all down. You may not think it's important but somebody may.' "
Not much escaped Grinnell's eye, or ear: "Have just heard the loud, hard clattering call of a belted kingfisher. ... As I sat down, four deer were walking about. The doe has now just gotten excited and given eight rather loud snorts, in irregular succession."
Perhaps most important, he punctuated the journal entries with his precise whereabouts: "At 7,000 feet, heard a very loud pounding. I followed the racket and came across a pileated woodpecker."
Nearly a century later, as Patton began retracing Grinnell's footsteps through Yosemite on a 2003 project funded by the museum and the park service, he turned to those old journals as a yardstick.
"The beauty of the field notes is they describe in great detail where Grinnell was camping and where he set his trap lines," said Les Chow, a data manager for the park service. "We can often go to the exact same place and see what's there now."
Although Patton's expeditions resemble Grinnell's, much has changed.
Grinnell killed what he caught, often in spine-snapping traps called "museum specials." Patton releases most of his captives, keeping only a few for specimens. The crackle of Grinnell's campfires has given way to the hiss of a cook stove. And while Grinnell's camp mates were mostly men, women are a big part of Patton's camps, most frequently his wife, Carol, who sets and checks traps with him.
In Grinnell's day, the piñon mouse was trapped in the piñon pine forests of the eastern Sierra at about 7,000 feet.
In 2003, Patton opened a trap near the wind-swept base of Mount Lyell at 10,240 feet and found one very upwardly mobile piñon mouse, an animal he nicknamed "Dumbo" for its huge ears. "What the heck are you doing here?" Patton recalls asking the mouse.
"All of us were pretty surprised," said Chow, who was camping with Patton. While rodent populations naturally expand and contract dramatically, Chow said he believes it's likely that global climate change has pushed the mouse up the mountain.
"Historic records for Yosemite indicate there's been about a 5-degree Fahrenheit (increase) in the maximum summer temperature for any given elevation," Chow said.
Other changes began to turn up as well.
The bushy-tailed wood rat -- known widely as a pack rat -- was a frequent casualty of Grinnell's traps. Patton rarely finds one. "They are less than uncommon," Chow said, asking: "Where have they gone?"
Water shrews were abundant in Grinnell's day, too. "Now, if you happen to see one, you consider yourself pretty lucky," Chow said.
But nothing has faded from the Yosemite landscape as thoroughly as the shadow chipmunk. "If you read their notes, they saw it every day," Patton said.
Today, it is a ghost. Patton has found only four -- a mother and three young. "We're never going to learn about the biology of the animal here in Yosemite, because we can't find them," he said.
Neither Chow nor Patton can explain the exodus completely, but geography and climate offer a clue. Yosemite is at the southernmost, warmest edge of the shadow chipmunk's range. A hotter park may simply not be to its liking.
Chipmunks point the way
The golden-mantled ground squirrel is moving higher in Yosemite, too. But few things are shifting upward there quite as rapidly as the alpine chipmunk.
As Grinnell's team fanned out across Tuolumne Meadows in 1915, the petite chipmunk with a striped face and button brown eyes seemed to be everywhere.
"This afternoon, I noted some alpine chipmunks feasting on a sandwich I had thrown out," wrote one member of Grinnell's team while camped at Tuol-umne. "First one, then another would nibble at it."
Don't bother trying to throw scraps to alpine chipmunks at Tuolumne today. Not only is it against park rules, it would be a waste of time.
"They're not there now," Patton said. "We looked for them extensively."
Over nine decades, the chipmunk has given up 2,000 feet of ground in Yosemite -- an average of roughly 20 feet a year. Maybe it's the rising temperatures that it does not like.
Or perhaps it is the landscape changes that follow climate change -- such as the creep of conifers up the mountain -- that are pushing it higher onto the talus slopes. Alpine chipmunks prefer open areas, not shadowy forests.
"Climate change doesn't involve just warming temperatures," said Chow, the park service data manager. "It involves changing rainfall patterns, changes in the timing and deposition in the amount of snow.
"We know chipmunks feed a lot on seeds. If we have a change in the pattern of snow deposition, there's a good likelihood we'll see changes in the distribution of plants. If that happens, the plants they rely on may go away."
Whatever the reason, time seems to be running out. If the chipmunk continues its pace of upslope retreat, it will start running out of real estate in 35 to 40 years. That could trigger other changes that might cascade through the mountain ecosystem and perhaps even splash into human society.
"We don't know whether ... if an alpine chipmunk is lost from the high Sierra, it will have any incredibly detrimental effect to human welfare, but it's possible that it could," Patton said. "The big concern is that these changes are happening so fast that we don't have a chance to understand both why they are happening and what the potential effects might be until it's too late."