In Hawaii, bird’s genetic trail leads from island to island

When Japanese bush-warblers (Cettia diphone) were introduced to Oahu in the 1920s, it might not have been good for native wildlife, but it turned out to be helpful for researchers. As the birds made their way to five of the main Hawaiian Islands in the 1990s, it gave researchers the perfect opportunity to look at genetic changes in a newly introduced species.

“The idea that we could use genetics to track their movements from island to island was really exciting,” said TWS member Jeff Foster, an associate professor at Northern Arizona University.

In a study published in The Auk: Ornithological Advances, researchers collected blood and tissue samples from 147 bush warblers to test the genetic diversity of the different populations.

“Working on native birds is really satisfying but logistically is very challenging,” said Foster, lead author of the study. Many native Hawaiian species are isolated on the tops of mountains that are difficult to access, he said, but “introduced birds have very few of those challenges. They’re everywhere.”

Traveling to different islands to sample the birds, Foster and his colleagues found evidence of genetic drift. In other words, random chance has allowed for genetic differences to occur in birds at various sampling sites. Moreover, at the introduction site of Oahu the birds had the most genetic diversity, but farther away there was less diversity. The Big Island, which was colonized last, had the least diversity. Only time will tell what happens to that diversity, especially with continued dispersal of birds among islands, Foster said.

“We had the potential to see evolution happening on a time scale that’s much more rapid than we normally think of,” he said.

But what surprised the researchers was that there was some evidence of distinct genetic groups on each island. That’s something they hope to look into further, as well as variation in the birds’ songs from island to island. Foster said he’s also interested in determining if these nonnative species are negatively impacting the native species through direct competition.

“Like any good research study, this left more questions than answers in the end,” he said.

But the next major step is determining if the genetic drift pattern is universal for the other ~55 introduced bird species in Hawaii, he said. “There are many other species to potentially look at,” he said.

Header Image: A Japanese bush-warbler sings on a tree branch in Japan. After introduction to Oahu in the 1920s, the species naturally colonized the remainder of the main Hawaiian Islands and genetics is piecing together this colonization history. ©Stuart Price