Abstract

We combined data on morphology, behavior, and gene sequences to document the first known case of hybridization within the thrush genus Catharus . During June 2008 at a montane forest site in south-central Vermont, we observed a male bird that repeatedly exhibited song characteristics of both Bicknell's Thrush ( C. bicknelli ) and Veery ( C. fuscescens ). Handheld examination determined the bird to be a yearling male with plumage characteristics predominantly of Veery and morphometric traits within the ranges of both Bicknell's Thrush and Veery. While the hybrid vocalized only with Bicknell's Thrush calls, its songs were reminiscent of both Veery and a mixture of Bicknell's Thrush and Veery. Mitochondrial DNA (NADH dehydrogenase 2 and cytochrome b genes) revealed the bird's mother to be a Veery, and nuclear data (β-fibrinogen 7 and myoglobin 2 introns) revealed DNA of both Veery and Bicknell's Thrush, supporting Bicknell's Thrush as the father of the hybrid. This hybridization is notable given that Bicknell's Thrush and Veery generally breed in different habitat types at different elevations. This discovery is also important in light of the vulnerable conservation status of Bicknell's Thrush and recent declines in Veery populations across much of the species' breeding range.