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Small Mammals on the Move in a Warming Yosemite

Over the last century, small mammals in Yosemite National Park have been on the move.  A recent study published in today’s issue of Science finds that as temperatures have warmed (a 3-degree Celcius increase in the park’s night-time low temperature) and Sierra glaciers have continued to melt, small mammals like mice, shrews, and chipmunks have moved to higher elevations or reduced their ranges in response to the climate.As part of the Grinnell Resurvey Project, a team from UC Berkeley’s Museum of Vertebrate Zoology headed up by professor Craig Moritz recently documented these changes in Yosemite by conducting a survey of the animal populations and comparing their data with an extensive data set collected in the same locations by field biologist Joseph Grinnell in the early 20th century.Of the 28 small mammals observed in the study, half had expanded their range upslope by more than 1,600 feet.

Since the higher up you are, the cooler the temperatures tend to be, recent research suggests that the mammals already living at high elevations may eventually face “mountaintop extinctions,” as they run out of room to climb higher if temperatures continue to rise. For example, the alpine chipmunk, which in 1918 was common at 7,800 feet, was recently nowhere to be found below 9,600 feet, according to the study.

Scientists acknowledge that changes in populations and animal communities are natural, but, Moritz says, what is less common is the speed with which these changes occured.