The biodiversity crisis is often defined by extinctions, the many species that are being completely lost. And that's important: the extinction rate today is estimated to be 1,000 times greater than that before humans. But the new study, published Thursday in the journal Science, shows that counting individuals of more common species can paint a grim picture. "The overwhelming focus on species extinctions, however, has underestimated the extent and consequences of biotic change," write the authors in the paper. As Arvind Panjabi, co-author and avian conservation scientist at the Bird Conservancy of the Rockies, says: "For the first time, we've combined estimates of [bird] population size with trends of population change."