Birds are doing it; plants are doing it. And it has nothing to do with Valentine's Day or spring flings. They are shifting their ranges in response to the effects of global warming at continental and local scales.
Fresh evidence comes from a pair of studies published Feb. 10. One comes from the National Audubon Society. The second comes from a team led by Theresa Crimmins, a scientist in the Office of Arid Lands Studies at the University of Arizona in Tucson.
Aside from the changes each study documents, the two efforts also highlight the increasingly important role citizen-scientists play in helping ecologists track shifts in plant and animal behavior and distribution. The next opportunity to take part comes up Feb. 13-15 with the Great Backyard Bird Count, run by Cornell University's Lab of Ornithology in Ithaca, N.Y.
For their work, Audubon Society scientists drew on data gathered during the past 40 years during the society's annual Christmas Bird Count project. They've documented [PDF] what they call a significant northward shift in early-winter quarters for 107 of 305 observed species. On average the species studied – including some that headed south – shifted their early-winter quarters by 35 miles.
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.
Some 93 plant species, roughly 26 percent of those Bertelsen tracked, flowered at significantly higher elevations during the second half of the period compared to the first half. The change is "concurrent with significant increases in summer temperatures across the region and are consistent with observed changes around the globe," the team writes.
Wanted: 40,000 observing sites
Crimmins's results are among the early ones stemming from the establishment of the USA National Phenology Network, a federally funded effort to track a range of changes that global warming is bringing to natural systems in the United States. It's part of a broader international effort to track shifts in plant, insect, and animal behaviors that are tied to changing seasons and have interlaced effects on breeding and life cycles.
Scientists are moving ahead on a modest network of heavily instrumented environmental observatories across the continent. But a handful sat back and thought bigger.
"Let's get citizen-scientists involved and pump things up to 40,000 observing locations," says Jake Weltzin, a US Geological Survey scientist and the executive director of the USA-NPN program, during a recent interview in his office just off the University of Arizona's campus.
The bird-watching efforts by Audubon and Cornell were clear models, adds Crimmins. "Those are some of the best data sets we have to infer the effects of the changing climate on natural resources," she said during the chat with Dr. Weltzin at the USA-NPN's coordinating center.
Indeed, she is interested in finding and using so-called legacy data sets – information gathered by people over long periods of time. Bertelsen's records represent one example. So do the data gathered by Henry David Thoreau. Last fall, a team led by Harvard University's Charles Willis published a study showing how a changing climate has led to lost plant species around Concord, Mass., since Thoreau's time. The team says its results suggest that climate change has altered the species mix, largely as a result of changes in flowering times.
And as word of the USA-NPN's work spreads, the program has started to get phone calls from people with potential useful legacy data, Crimmins says.
During a phone chat, he says that Project Feeder Watch – now entering its 22nd season – attracts roughly 15,000 participants a year; 75 percent are repeat participants.
But there's always room for more, particularly for people who are interested in helping over the long haul.
He counts 100 participants who have been at it since the program began, giving researchers a unique set of data among the careful work done by the other 14,900 participants. Demographics is taking its toll on this subset of the most seasoned observers, he says.
With some of the labs' entry-level monitoring programs, such as the Great Backyard Bird Count, the program hopes to continue refreshing the ranks of participants, including those whose interest remains kindled for decades.