Dynamic rivers have contributed to the rich bird diversity of the Amazon.

One of the most controversial cases in evolutionary biology is how the Amazon became so diverse? A new bird-focused study examines how the movement of rivers in the Amazon has contributed to the region's incredible biodiversity. 

Unfortunately, the results also show previously unknown bird species in the Amazon are found only in small areas adjacent to this dynamic river system, placing them at high risk of immediate extinction.

"Early evolutionary biologists such as Alfred Russell Wallace noted that many primate and bird species branched off on opposite banks of rivers in the Amazon, and ornithologists now know that rivers are in one course or another linked to the origins of many bird species, said study author Lucas Muscher, a postdoctoral fellow in the Academy of Sciences at the University of Drexel and a recent Ph.D. in comparative biology. graduated from Richard Gilder High School at the American Museum of Natural History. "Furthermore, the accumulation of geological evidence suggests that these flows are highly dynamic, moving across the South American landscape for relatively short periods, on thousands or tens of thousands of years.

"Although birds can fly, our study confirms that current rivers in the southern Amazon rainforest, even relatively small ones, are highly effective in isolating populations of these six species, leading to genome divergence and eventual speciation," said the study's senior author. Joel Cracraft, curator of Lamont and chief curator of the museum's ornithology department.

However, because these rivers move through the landscape at different timescales, their movements can have other consequences for bird species: when river relocation occurs rapidly, bird populations on either side can merge before they can be distinguished; when river changes are slow, species have a longer time to diverge; and when the river changes moderately, the bird populations diverge and then merge and merge as the river moves.