Much of my research involves using DNA sequences to reconstruct phylogenetic hypotheses of songbird relationships. Such phylogenies, the cornerstone of modern comparative methods, provide a necessary framework for studying the evolution of various avian traits. Characters examined in this context can include behaviors (such as migration), morphological traits (such as size, osteological characters, or plumage coloration), or distributions through time and space (biogeography). The latter is the focus of much of the research done in my lab, where we begin by identifying the units of biodiversity and then attempt to understand the origin and maintenance of this diversity in an ecological and biogeographic context.

Two long-term studies in my lab are designed to investigate the evolution of distributions and diversity of New World birds (mostly songbirds).  In the first, I am collaborating with Drs. Garth Spellman and Scott Edwards on a comparative phylogeographic study of birds that occur in montane pine and pine-oak habitats ("sky-islands") of western North America.  We are interested in determining whether the birds breeding in these habitats are structured into genetically discrete evolutionary units and in assessing the amounts and directions of gene flow occurring between such units.  We can then ask how common geographic patterns of genetic diversification across this suite of co-distributed bird species can be interpreted in light of known episodes of change in earth history (e.g. glacial advances, regional uplifting, etc.).  A second focus of my research involves genetic sampling across several lineages of highland and lowland tropical bird species from throughout their ranges in Central and South America.  In this work, I am investigating how the Isthmus of Panama completion some 3 mya affected diversification rates in this region, and more generally, how the "Great American Interchange" played out for avian taxa.

As a museum-based scientist, I'm also interested in traditional museum pursuits such as the taxonomy and classification of birds.  Where earlier taxonomists used morphological, behavioral, and vocal characters to delimit species and define the relationships among them, I use molecular characters instead. Presently I am collaborating on an "avian tree of life" project with researchers from three other institutions, in which we are determining relationships among all New World nine-primaried oscine species (around 823 taxa).