|Red Crossbill. Photo Copyright Michael Woodruff|
A third example is the Veery (Catharus fuscescens), a bird with arguably the most beautiful song in North America. A relative of the American Robin and other thrushes, the Veery is an adept songster. Within its song, their are actually two voices harmonizing each other with their own complex series of notes, slurs, and trills, but it's hard to discern this by listening to it at normal speed. But when slowed down to about 1/4 the speed, you can hear the intertwined voices of each side of the bird's syrinx, and the harmonies that result in the amazing song of the Veery. Read more from where I got this information at Earbirding.com, where you can also hear the individual voices within the Veery's song, as well as slowed down versions of the individual and the full songs. It's pretty awesome.
The complexity of bird vocalizations is something that recent technologies have allowed us to understand to a greater extent than ever before, and I'm sure there will be more to come.