Cassin's Vireo Identification

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The Four Keys to ID

  • Size & Shape

    A small but sturdy songbird, with a fairly thick, short bill and relatively long wings and tail.

    Relative Size

    Larger than a Red-breasted Nuthatch, smaller than a Red-eyed Vireo.

    Relative Sizesparrow or smallersparrow-sized or smaller
    Measurements
    • Both Sexes
      • Length: 4.3-5.5 in (11-14 cm)
      • Weight: 0.5-0.6 oz (13-18 g)
      • Wingspan: 9.4 in (24 cm)

Regional Differences

The cassinii subspecies occurs across most of the species’ range in western North America. The lucasanus subspecies occurs only in southern Baja California, Mexico, and has a larger bill than cassinii. The cassinii form migrates, whereas lucasanus is a permanent resident in mountains at the tip of the Baja California Peninsula. As is expected in a migrant, the migratory subspecies has slightly longer wings than the sedentary lucasanus.