This is significant, because it runs counter to a prevailing view in biodiversity circles, the study's authors say. "A new distinctive group, like bumblebees or tunafish, first evolves, and, if conditions are right, it quickly radiates to produce a large number of species," says co-author Arne Mooers of Simon Fraser University in Canada. "These species fill up all the available niches, and then there is nowhere to go. Extinction catches up, and things begin to slow down or stall. For birds the pattern is the opposite: Speciation is actually speeding up, not slowing down."