Expanding Virginia’s warblers retain uniform gene flow

It’s not easy to find Virginia’s warblers (Oreothlypis virginiae) — especially given their shy, elusive behavior.

Researcher Christine Bubac learned this firsthand when she used mist nets to capture the nine-gram songbird species in the Black Hills of South Dakota. She wanted to catch the birds to study the genetic diversity of this isolated population compared to Virginia’s warblers in other regions.

“My co-author and I set out to look at how population connectivity impacts genetic variation during a contemporary range expansion,” said Bubac, a Ph.D. student at the University of Alberta and the lead author of the study published in The Auk: Ornithological Advances.

Annual breeding bird surveys showed Virginia’s warblers arrived in the Black Hills fairly recently in 1997. While most Virginia’s warblers are concentrated in the southwestern United States, it appears the species’ range is expanding northward, resulting in populations in northern Colorado, Wyoming and South Dakota’s Black Hills, according to Bubac.

Bubac mist netted 20 Virginia’s warblers, collected feathers from the birds to do a genetic analysis, and then subsequently released the individuals. The team then collected additional samples of the species throughout their breeding range from museum and university collections. After comparing DNA samples, she and her team found that the Black Hills population seems to maintain continuous gene flow with the rest of the species. This means that new birds are likely continuing to arrive in the area, and there is less of an inbreeding risk for the species.

The reason for the birds’ expansion is likely due to the nature of the species, according to Bubac. “It has a strong dispersal capability,” she said. “Among warblers, they’re strong flyers and have the ability to track their climatic niche to colonize habitable areas.” Bubac added that the birds’ expansion is most likely a natural post-glacial range expansion, initiated by changing environmental conditions.