Bird song fills a northeastern Adirondack forest on a sunny May morning. Two notes announce a black-capped chickadee. A red-breasted nuthatch blurts out honk, honk, honk. Then: see-bit see-bit see-bit titititititi. “That’s him!” says Mads Moore, recognizing a Nashville warbler. 

Moore and two other researchers from Pennsylvania State University stand single file on one of the grown-over logging roads that spiderweb through the Adirondack Land Trust’s Glenview property off NYS Route 86 in Harrietstown. The 238-acre parcel includes meadow, forest, and bog—attractive bird habitats that put Glenview on a list of nine sites the Penn State team will visit on a 14-day trip. They’re looking for Nashville warblers and common yellowthroats, members of North America’s wood warbler families, and the subjects, respectively, of research by Ph.D. candidate Lan-Nhi Phung and Marcella Baiz, Ph.D., who stand next to Moore. 

Moore spots a flash of yellow in trailside shrubs and points out the Nashville warbler for Phung. “Closest approach,” Phung whispers. Moore notes the location of both humans and bird. There are two breeding populations of Nashville warblers in North America: western and eastern. The western population sticks to Idaho, Washington, Oregon, and California. The eastern population visits the Adirondacks, the southern end of a breeding range that extends north to Canada’s Hudson Bay and stretches from the Atlantic Ocean to Saskatchewan.  

The Nashville warbler at Glenview flits to a balsam tree. Phung pulls a handheld Bluetooth speaker from her backpack and uses her phone to play a recording of the western population’s song. She watches for behaviors—more frequent singing, flying to the song source—that could indicate the eastern bird identifies the western as the same species and therefore a territorial threat. This Nashville warbler sings, then moves to a nearby tamarack, its yellow bib on display. Phung explains this response is unclear. That’s why she needs to complete this process with at least 25 Nashville warblers on this trip, then perform a statistical analysis. 

Phung unzips her backpack and takes out a measuring tape. She holds the case and Baiz takes the hook end, stepping off trail to unspool the steel tape to the balsam selected by the Nashville warbler. She calls out numbers, which Phung repeats for Moore to write down. Then the trio measures the closest approach point. Tools stowed, backpacks shouldered, the group moves east along the path. The bog lies ahead. The work continues.