Such changes have "implications for the animals that are dependent on this plant," Weltzin said, as he stood beneath a blooming red maple in late February. By the time the animals arrive, "the flowers may already be done for the year." The animals may have to find a new food source.

"It's all a part of life," Weltzin said. "Timing is everything."

On the Net: National Phenology Network: www.usanpn.org/

IPCC report on phenological changes:

http://www.ipcc.ch/pdf/assessment-report/ar4/wg2/ar4-wg2-chapter1.pdf

National Park Service on cherry blossoms:

www.nps.gov/nama/planyourvisit/cherry-blossom-bloom.htm

University of California at Davis butterfly changes:

butterfly.ucdavis.edu/education/stat2/data

University of Wisconsin-Milwaukee lilac and temperature data:

tinyurl.com/28ts39