Yellow-rumped Warbler — Wings of NH

What you notice first

In an October migrant flock, a small grey-brown bird that flicks up a bright lemon-yellow rump patch every time it moves — hence the field name, "butter-butt."

Voice

A loose, musical trill that rises or falls slightly at the end; the call, given constantly in migration, is a hard, distinctive "check."

Where & when

Spruce-fir and mixed conifer for breeding in the Whites and North Country. On migration — May, and again late August through October — in nearly any habitat, often the most numerous warbler in a fall flock by an order of magnitude.

The warbler that breaks the warbler rules. Most of its family is gone from New Hampshire by early October, chasing insects south. Yellow-rumps stay latest and push through in the biggest numbers because they can digest the wax in bayberry and wax-myrtle fruit — almost no other songbird can — which lets them switch to a fruit diet when the bugs quit.

That flexibility is why you can still find one on the seacoast in December, working the bayberry in the dunes, while every other warbler is in the tropics.

Four marks in any plumage: the yellow rump, a yellow patch on each side of the breast, a broken white eye-ring, and white in the tail corners. Spring males add a slate-blue back and a yellow crown spot and are genuinely sharp.