Yosemite Fauna on the Up and Up
Scientists studying Yosemite National Park's bountiful wildlife have found that several animal species have moved to higher altitudes, an uphill migration possibly spawned by the grinding effects of global warming on one of the nation's most protected wildernesses.
The team of scientists from UC Berkeley's Museum of Vertebrate Zoology made the discovery while retracing the pioneering research of biologist Joseph Grinnell, who about 90 years ago cataloged the park's menagerie of mammals, birds and reptiles.
Over the last three summers, the Berkeley researchers revisited many of the spots Grinnell plotted in his landmark study. What they found was an environment that has seen a remarkable shift in many of its wild inhabitants.
Several species of small rodents that once lived in Yosemite's lower elevations have now moved higher up the Sierra's gnarled granite frontier, in some cases shifting their range by as much as 3,000 feet.
Yosemite Valley, meanwhile, has seen a 50% turnover in the types of birds it harbors, and several species have spread to far higher elevations than ever seen in Grinnell's day.
Part of the shift, the scientists said, could be explained by natural variations that species see over time, or by alterations in flora and the forest canopy caused by a century's worth of aggressive wildfire suppression. The California pocket mouse, for instance, may have expanded its range nearly 3,000 feet higher because the chaparral it inhabits has spread farther up the park's western slope.
But in high-elevation spots where fire is not a factor, several small mammal species have fled farther uphill, prompting researchers to suspect that larger forces are at work.
"I didn't go into this expecting any shifts, to be quite honest," said James Patton, the museum's curator and an emeritus professor of integrative biology. "But the changes are clear-cut. The data record is very strong. While the interpretation as to what these changes mean remains open to discussion, they are consistent with expectations of global warming."
Several other studies have documented similar environmental changes in the Sierra, among them disappearing glaciers and alterations in the growth pattern of trees in some types of soil.
Over the last century alone, Patton said, the average annual temperature in Yosemite has risen by 9 degrees Fahrenheit.
