Three chickadees clung to a suet feeder outside Denver, but one of them looked different from the others. Unlike the two Black-capped Chickadees, this one had a faint white band above its eyes, characteristic of a Mountain Chickadee. In July, at the Randall Davey Audubon Center in Santa Fe, another birder spotted a chickadee with a Mountain’s white eyebrows and a Black-capped’s buff sides and white-edged wings. Similar birds have popped up in Salt Lake City, Albuquerque, and other Rocky Mountain metros. 

Prior to eBird’s creation in 2002, the scientific literature held only three records of hybridization between Black-capped and Mountain Chickadees, each report more than 25 years old. But in the past few years, Kathryn Grabenstein and Scott Taylor, evolutionary biologists at the University of Colorado Boulder, noticed that eBird users commonly spot hybrids of the two species in the West. The platform includes more than 800 such reports today, many of them from cities and towns. The researchers decided to look further into the phenomenon.  >>>READ MORE