What can cause species that have been separate for thousands of years to suddenly start interbreeding (hybridize)? In songbirds, species are often kept separate from one another due to different songs, habitat preferences, or other behavioral differences. Along Colorado’s Front Range, black-capped and mountain chickadees have recently begun to interbreed. How could that be? What in their environment has changed to remove past barriers to reproduction between these species? CU Boulder’s speciation sleuths, Dr. Scott Taylor and Kathryn Grabenstein, are tackling this question through research in backyards and wildlands around the Front Range to get to the bottom of this mystery. Explore the videos and links below for more information and lessons featuring these researchers and the hybridizing chickadees!