For others, the researchers pored through museum collections, interviewed aging amateur lepidopterists and read old scientific reports. All that just to compare the locations of butterflies' old haunts with sites of their current digs. Of Europe's 440 species of butterflies, the team found good historical records for only 183 species. The study winnowed those to the 35 that could migrate because food and habitat were available beyond their range. The team found northward movement in so many species and spread over such a broad region of Europe, he says, that the cause must be something very general.
Climate change fits the bill.
Crick's own work links earlier egg-laying by British birds to this century's warmer spring temperatures. Butterflies in Europe aren't the only species that will shift in response to global warming, says ecologist Terry Root of the University of Michigan in Ann Arbor. Birds, too, are moving out of the neighborhood as the temperatures increase. In northern Michigan, she's finding that although the migratory birds that eat spruce budworms are moving farther north, the spruce budworms are not. If the birds no longer keep the insects in check, the forests could suffer.