What makes one bird species turn into two species of birds?

A long-standing theory posited that a likely cause was drastic geographical changes, such as a river forming and cutting off members of the same species, leaving them in isolation for a long period of time. This isolation meant the two groups would eventually evolve so differently that they would become two distinct species.

This hypothesis was seen as the explanation for the multitude of species found in places like the rainforests of South America.

LSU scientists, along with other colleagues, are challenging that notion in a new study published in Nature .

“What we found is just the opposite. Stability is what you want,” said Robb Brumfield, LSU Museum of Natural Science director and one of the article’s authors.

In order to come to this conclusion, researchers looked at 27 bird lineages in South America to see when the different species emerged.

“What we found is most of the species in those lineages are way younger than the uplift of the mountains or river formation,” Brumfield said.

In other words, the large geographic boundaries created three million years ago when the Andes and the Amazon River formed couldn’t have caused the levels of species diversity they were seeing. The species they identified appeared to be on the order of about a million years old.

The researchers laid out their conclusion that new species creation is an ongoing process.

“We made the case in the paper that it’s really stability that’s the driver,” Brumfield said.

Stability lowers extinction rates, giving a species more time to flourish. But, as with the traditional conception of species formation, geographical isolation was considered a key factor. Instead of some birds being separated from others by a drastic event, however, the researchers had a calmer theory that they essentially wandered off to cross a river or mountain where they are isolated from the main population.

Over a large amount of time, this isolation can lead to the formation of a new species.

It’s the time, and consistent habitat to thrive, that makes the difference.

This idea of a continuing spectrum of species development is something that has been “lurking under the surface,” Brumfield said. Research on a single bird lineage, like a Toucan, found that the species differences within that lineage weren’t old enough to have been the result of major geological changes.

This new article, however, was the first time anyone has collected a very large set of information on multiple lineages of birds to gather enough information to see the gradual nature of the species formations, he said.

For decades, LSU researchers have been collecting birds with a large emphasis on South America, and the collection at the LSU Museum of Natural Science is impressive. It is that collection, along with the collection of other universities, museums and organizations, that made such a large study of species possible.

The research was paid for by the National Science Foundation and involved a long list of museums, organizations and universities including LSU. Some of those groups include the American Museum of Natural History, City College of New York, Universidad de los Andes in Colombia, Universidad Central de Venezuela, University of California Los Angeles and the University of Georgia.

Follow Amy Wold on Twitter, @awold10.