Blue-headed or Cassin's Vireo?
Vireo solitarius or Vireo Cassinii

Montrose Point, Lincoln Park, Chicago
Cook County, IL
24 September 2017


Presumbly this is a Blue-headed Vireo (Vireo solitarius), as that is the regularly occurring form of the Solitary Vireo complex in this area. Nonetheless, how does one conclude definitively that this is not a vagrant Cassin's Vireo (Vireo cassinii)?

This page was last updated on 24 September 2017.
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