In fall migration, the similar plumages of juvenile female Rufous and Allen’s hummingbirds, female and juvenile male Broad-tailed Hummingbirds, and female and juvenile male Calliope Hummingbirds cause a lot of confusion, especially when they stray east of their usual migration routes.
Shape is one of the first clues for quickly separating these doppelgangers. Broad-taileds are long and relatively slim, with proportionally smaller heads, longer, often slightly decurved bills, longer wings and tails, and relatively broad primaries except for the outer two (P9-10). Rufous and Allen’s are relatively compact, big-headed, and barrel-chested with tapered outer primaries that give the folded wing a scythe-like shape. Calliopes have even bigger heads, plus shorter bills, shorter tails, and broad, curved outer primaries distinctly different from either Broad-tailed or Rufous/Allen’s.
On the fanned tail, the amount and distribution of rufous coloration is important but variable within as well as between species. In juvenile female Rufous/Allen’s, R2 has rufous across the entire base or on both the inner and outer vanes divided by a stripe of green. In Broad-tailed, R2 is predominantly bright green with a partial border of rufous along the edge of the outer vane and variable black at the tip. The stubby tails of Calliopes are predominantly dull green, black, and white, with significantly less rufous in the outer four pairs of tail feathers than either Rufous/Allen’s or Broad-tailed (typically most conspicuous on the basal edges of R2-4 in juvenile males and adult females). The number of outer tail feathers with white tips is often helpful in distinguishing juvenile females (typically R2-5) from adult females and juvenile males (typically R3-5), but it’s not helpful in separating species.
There are other, more subtle clues to separating these often confusing species, but shape and tail pattern will resolve the vast majority of ID dilemmas.
The illustration above is styled after the all-new plates in the forthcoming successor to A Field Guide to Hummingbirds of North America in the Peterson Field Guide Series. The new guide will be published by Princeton University Press should be available from your favorite bookseller in early 2022.