Highlighting Student Research: Discovery of a New Warbler Hybrid
While conducting field work in the Adirondacks Mountains of New York in 2009, I captured a warbler that didn't quite look right. Because of an unusual mix of field marks, I suspected the bird might be a hybrid (a cross between two different species), and collected it as a specimen. Dave Ermacor, a student at Utica College, took on this project for his senior independent research, and helped me and collaborator Jeremy Kirchman sort out the details.
To determine exactly what we had on our hands we first sequenced a mitochondrial gene. Mitochondria are inherited maternally, meaning this DNA sequence would tell us what species the bird's mother was. To our surprise the mitochondrial sequence was a match for an Orange-crowned Warbler (Oreothlypis celata )- which do not regularly breed in New York. In fact there are no breeding records for Orange-crowned Warblers anywhere in the northeastern United States! (They normally breed further north in Canada).
Next, like an ornithological version of the Maury Show, we set out to determine who the father was, or at least what species the father was. To do this, we sequenced a nuclear gene, which is inherited from both parents and can be used to determine paternity. The results suggested our bird's father was a Nashville Warbler (O. ruficapilla ), which do regularly breed in the Adirondacks. Our hypothesis that our specimen was a hybrid was supported! |
Variable sites in DNA sequences comparing hybrid to Orange-crowned Warbler (celata) and Nashville Warbler (ruficapilla). Red sites show DIFFERENCES between the hybrid and parent species. This shows that the mitochondrial DNA likely comes from an Orange-crowned Warbler, but the nuclear DNA comes from a Nashville Warbler.
We also compared the plumage and morphology of the suspected hybrid to known Orange-crowned and Nashville Warblers by measuring museum specimens. We measured the size and shape of the bill and the length of wings, tarsi, and tails for each species. The plumage of our hybrid was nearly identical to a Nashville Warbler (note the bright yellow belly, and white eye ring in the picture below). Morphological results supported our genetic results by indicating the hybrid is intermediate between Orange-crowned and Nashville Warblers.
Our finding is the first report of hybridization between Orange-crowned and Nashville Warblers, though hybridization in the wood-warbler family (Parulidae) is fairly common. This is at least the 73rd reported cross between two Paruild warbler species, and roughly 50% of the species in this family have been known to hybridize.
A paper describing our findings is currently in review.