The Voices of Birds: Call Dialects of the Evening Grosbeak

Birds, like people, have dialects. These intonations and manners of communicating can tell listeners where an individual is from, which other birds they associate with, and even what they prefer to eat.

Birds also have distinct modes of vocalization: songs—long, elaborate strings of notes used to attract mates and defend territories—and calls, generally brief vocalizations that communicate distinct social information, such as the presence of food, danger from predators, or affiliation. While bird songs are literally like human singing, calls function more like speech. Most dialects researchers have described in birds have been reported in songs, and are strictly limited to geographic boundaries. But in a few cases, calls are also distinct to populations. These calls might be compared to humans from different geographic regions speaking with unique accents.

Evening grosbeaks (Coccothraustes vespertinus) are finches that feed in coniferous forests. Their range covers much of North America, although they are in decline—the American Bird Conservancy’s 2014 State of the Birds report includes them for the first time on its watch list of 233 North American species “most in need of conservation action.” They’re one of several species that show great diversity of calls across populations. In a 2004 paper in the ornithological journal the Condor, Rodd Kelsey, Thomas P. Hahn, and I described five distinct call dialects for the species. In the map and chart on the following pages, calls are rendered as spectrograms—graphs of the pitch of a sound over time, generated from audio recordings of birds’ vocalizations. The y-axis is frequency—calls tend to range between 2 and 4.5 kilohertz, or three to four octaves above middle C on a piano—and the x-axis is time. Most calls last around 2 seconds.

In the map, the birds’ calls appear where they were recorded, showing that their dialects are not strictly limited to geographic boundaries. Instead, these birds maintain their accents just as humans do, advertising their origins as they move through space and time.