Cassin’s Vireo

Vireo cassinii

The Cassin’s Vireo, along with the Blue-Headed and Plumbeous Vireos, form a trio that prior to 1997, were lumped together as a single species: the Solitary Vireo. Each of the three have visual differences to help distinguish them from each other, but they also have general regional distinctions. The Cassin’s Vireo is more of a western bird, the Plumbeous a mid-continent bird, while the Blue-Headed Vireos live in a more eastern region of North America. All three members issue songs that sound remarkably similar. I liken their songs to a “call-and-answer” sequence, beginning with an up-slurred “two-wheet” question, followed by down-slurred “two-woo” answer.

Today, science recognises two subspecies of Cassin’s Vireo:

• V. c. cassinii breeds from southern British Columbia, and southwestern Alberta (Canada) and south into Washington, Montana, all the way to California and east into northern Baja California (Mexico). They spend winters from southern California to Arizona and south to Oaxaca (Mexico).
• V. c. lucasanus lives in southern Baja California (Mexico).

I once met a Cassin’s Vireo in my southern California yard, but, as with most of us, the first time meeting was the most memorable. Mine came while I was working on the San Diego County Bird Atlas in 2004. Most of the work for the book was complete, but some species still had no images available for the publication. I made it my mission to gather images of as many of these missing species as I could. The Cassin’s Vireo was one such bird, and I captured an image, along with other species, that became a part of the published account.