From finches to flycatchers, songbirds are the poster children for avian diversity. But songbirds aren't the only reason birds are so varied and interesting: Bursts of new species appeared among island birds, waterfowl, woodpeckers, hummingbirds, and gulls, among others, at various times during avian evolution, researchers report online today in Nature. A new avian family tree, represented here as a circle, reveals this increasing rate of diversification of feathered creatures  during the past 50 million years. At the circle's midpoint sits the avian ancestor; lines branching out from the center reveal how and when new species arose. The concentric shaded areas each represent 20 million years, and the rim, with its dense array of tips, shows the world of birds today. The lines are color-coded to designate how fast new species arose along that lineage—blue being the slowest and red being the fastest. Researchers compiled this tree over 5 years, using genetic data already in public databases and other information to estimate how the known 9993 bird species are related to one another. They studied the ranges of all the birds, looking for geographic patterns of bird evolution. Some bird lineages, such as woodpeckers, split into new species often, while nearby groups, such as hornbills, did not, they note. More diversification occurred in the Western Hemisphere compared with the Eastern Hemisphere. The tropics, despite their current species richness, were not diversification hotbeds but likely have so many species because the ecosytems there have been around for such a long time, says study leader Walter Jetz, an ornithologist at Yale University.
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