As the planet warms, the temperatures that trigger spring arrive earlier. But not everything's adjusting on the same schedule. Flowers open before their insect pollinators come out, and birds return from migration too late to find their usual bug meals. Detailed study of ecological mismatch requires equally meticulous observations of historical timing—and a Boston University lab has found a trove in the journals Henry David Thoreau kept in Massachusetts in the mid-1800s. "They're probably the oldest detailed records of flower and bird-migration times in the United States," says Richard Primack, a conservation biologist who runs the BU lab. The diaries, together with more recent data, reveal an ecological system in flux.