Cassin's Vireo at 2404 Central Ave, Boulder

[van....@gmail.com]

I parked my car right in front of the building shown in Richard Pautsch's post (5757 Central Ave) this morning to see if I could find an unusual Vireo. As soon as I opened my car door, I heard a Vireo call and set of on following him around the building next door, 2404 Central Ave. 

However, after getting a few good looks at the bird, and recording the call I concluded that I was looking at a Cassin's Vireo. I had just observed a Plumbeous Vireo near Chautauqua, Boulder, and the bird on Central Ave looked a lot like that Plumbeous except it had some yellow shading along its flanks. Merlin couldn't decide between Cassin's and Plumbeous, and I've added the recording to my checklist. https://ebird.org/checklist/S138704396

Van Rudd

Louisville, CO