While most birds either migrate or remain resident in one region, the Audubon's warbler, with habitat ranging from the Pacific Northwest to Mexico, exhibits different behaviours in different locations.

The northern populations breed and migrate south for the winter, while southern populations have a tendency to stay put all year long.

Evolutionary biologists have long been puzzled by research that indicates some Audubon's warblers share the same mitochondrial DNA (mtDNA) with myrtle warblers - a different species of songbird that migrates annually to the southeastern US, Central America and the Caribbean - even though they look dramatically different.

"Mitochondria are only passed down from mothers to their offspring," said David Toews, a PhD candidate in University of British Columbia's Department of Zoology.

"So it's a very useful marker for differentiating species. In this case, finding two species of songbirds sharing the same mtDNA is very surprising, so we set out to find out why," Towes said.
By analyzing genetic data and stable isotopes in feathers, and by measuring oxygen consumption of the mitochondria in their flight muscles, Toews and fellow researcher Milica Mandic pinpointed the precise geographical location near the Utah-Arizona border where the myrtle warblers' "wanderlust" genes displace the Audubon warbler's ancestral mitochondria.
This region happens to also be the transition zone where a change in the migratory behaviour of Audubon's warblers is seen.

"Our findings suggest that over generations, the Audubon's warbler may have co-opted the myrtle's mitochondria to better power its own travels," Toews said.
The study was published in the journal Evolution.


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