MacGillivray's Warbler Identification

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The Four Keys to ID

  • Size & Shape

    A compact, small songbird with a full body for a warbler and a thick neck. The bill is straight and thin overall, although heavier than many other warblers’ bills. The tail is medium length and the legs are fairly long.

    Relative Size

    Slightly larger than a Common Yellowthroat, slightly smaller than a Pine Warbler.

    Relative Sizesparrow or smallersparrow-sized or smaller
    Measurements
    • Both Sexes
      • Length: 3.9-5.9 in (10-15 cm)
      • Weight: 0.3-0.5 oz (9-13 g)
      • Wingspan: 7.5 in (19 cm)

Regional Differences

Ornithologists currently recognize two subspecies: tolmiei that breeds on the west side of the Cascades and Sierra Nevada, from Alaska to southern California (the Pacific Slope), and monticola that breeds east of that region, in the Rocky Mountains from British Columbia to Arizona. Plumage tones differ markedly, with tolmiei a saturated yellowish olive above and bright yellow below, and monticola more grayish olive above and a paler greenish yellow below. The small, isolated population in northern Mexico is genetically very distinct from the nearest U.S. populations and probably diverged over a million years ago, during the early Pleistocene.