During one of my all-time favorite reporting trips, in the summer of 2005, I hiked through a chilly Yosemite rainstorm to meet up with University of California-Berkeley mammalogist Jim Patton. Patton -- a veteran field biologist with more shipwreck stories than any one person should have -- was retracing the century-old steps of Joseph Grinnell, who surveyed California's wildlife back in the early 20th century.
Thanks to Grinnell's tireless travels and meticulous note-taking, Patton and his colleagues were able to repeat his surveys, and get a sense of how the state's wildlife had changed over the past 100 years. They'd found that four small mammal species had moved the top edge of their range uphill, and that two other high-elevation mammals -- the pika and the Belding's ground squirrel -- had drawn in the bottom edge of their ranges. Two other mammal species had shrunk their ranges dramatically, and had become extremely rare in the park.
Now, six years later, the Grinnell Resurvey Project has issued a full report on its work in Yosemite. The report confirms Patton's early findings: Of the 30 mammal and bird species studied, 14 show no significant change in their range over the past century, but 16 have shifted their habitats, with lower-elevation species expanding their range uphill and higher-elevation species retracting the lower limit of their range. While two data points do not a trend make, the pattern of the results suggests that many of Yosemite's critters are responding to climate change. With Grinnell's help, we can follow their tracks.
To see just how obsessive Joseph Grinnell could be, take a peek at digital images of his original field notes.
Joseph Grinnell, at home in the field.
Michelle Nijhuis is a contributing editor at HCN.