But averages mask the extremes. Some individual species spread farther afield. Among waterbirds in the survey, the Red-breasted Merganser topped the list at 317 miles. Among shore birds, the Black Turnstone moved up the map some 178 miles. And among land birds, the Spruce Grouse shifted north by 316 miles.
Human encroachment on habitat certainly played a role, scientists acknowledge, particularly among grassland birds. But they cite global warming as "by far the most probable cause," in no small part because the new locations could meet the birds' biological needs.
Flowering moves upslope
Dr. Crimmins's team's paper draws on a 20-year record of plants in flower gathered by David Bertelsen. He works at the University of Arizona's herbarium. At least once a week for more than 20 years, he's hiked some or all of the Finger Rock Trail in the Santa Catalina Mountains outside of Tucson.
The data come from hikes taken between 1984 and 2003. (That's 1,204 round trips of the full five-mile trail and 30 partial trips, for those of you with hiker's envy.) Mr. Bertelsen kept a meticulous record of the places along the trail where he saw plants flowering.
For the full trail, the hikes covered an elevation range spanning 3,100 feet to 7,258 feet above sea level. From an ecological perspective, that's the equivalent of a trek from southern Arizona to southern Canada. Weather data came from six sites at different elevations within 60 miles of the trail. This allowed the team to track temperatures in ways that wouldn't be distorted by features such as Tucson's urban heat-island effect.