A bird might, for instance, have the distinctive yellow patches on its wings, the golden head, and the jet-black collar of a golden-winged warbler but with the yellowish belly of a blue-winged warbler.
The physical differences between the mixed progeny and their pure counterparts can be subtle. Hybrids of golden-winged and blue-winged warblers are increasingly popping up across the Northeast and into Canada. Whether the bird is actually a hybrid is the question Vallender seeks to answer.
Each tube, carefully labeled and organized, holds a blood sample from a single warbler. “I love getting huge boxes of blood,” says genetic ornithologist Rachel Vallender as she pulls open a drawer full of small plastic vials in her laboratory at the Canadian Museum of Nature in Ottawa, where she’s a visiting scientist.