As with most birders, my head is on a swivel, and my ears are always perked. Even on a walk in the middle of Broadway being attentive can reveal a Peregrine Falcon soaring overhead, or Dark-eyed Juncos flitting toward Cal Anderson Park. My friends know I’m frequently distracted. On a recent urban walkabout, one such friend noticed my focus on the tree-tops of the street trees overhead. He asked what I was looking for.
“A Yellow-rumped Warbler — there, flitting between the upper branches.”
Setophaga coronata, roughly translated means “moth-eating” and “crowned.” The meaning of the Yellow-rumped Warbler’s scientific name is far from the first description that would pop into my head when thinking about the species. They are absolutely the most mobile species of warbler in our region, constantly flying out from treetops to catch insects on the wing. But, I don’t personally know them by their moth eating (despite being a known spruce budworm predator). Nor do I know them for having a crown, which is a largely indistinct trait, unless you are holding the bird in your hand.
One of the things Yellow-rumped Warblers are actually well known for is their tendency to eat more fruit than other warblers. Once considered two species, both the more Northerly and Easterly, “Myrtle” Yellow-rumped Warbler, and the Western, “Audubon’s” Warbler eat the waxy berries of myrtle and bay plants. Most other species of warblers would have a challenge digesting those berries and this allows Yellow-rumpeds to winter where their more insectivorous warbler relatives can not.
Warblers themselves are a fairly diverse group of New World songbirds that are well known for flashy plumage. All the warblers that visit the Hill are migratory to a certain degree. Some zip off to Mexico or Central America like a bunch of snowbirds. Others may stick around, or show up from the not too distant wilds of the Cascade mountains after breeding. I’m expectant of the first Wilson’s and Orange-crowned Warblers that show up in the spring, fresh from winter sun and adorned to retake their previous year’s territory. I enjoy the occasional wintering Townsend’s Warbler I see flitting in the top of a towering Douglas fir. But no other warbler species is as common, nor as easily seen as the Yellow-rumped.
Yellow-rumped Warblers exhibit what’s called facultative winter migration. This means they stick around, as long as there’s adequate resources and conditions. Other birds, like American Robins, hardy enough to stick around further north, can do the same thing. However, if the mercury dips too low or if there’s poor food availability, they will simply move on. This may seem like an obvious choice to us, but in most migratory birds, the urge to migrate is triggered by day length and other environmental cues; that dissipates during winter. With Yellow-rumped Warblers, it’s almost as if they are considering leaving, but don’t quite get around to it unless things get really bad. When spring rolls around and they head back to territory nearby, or even up in boreal forests to the north, they don’t have to travel all the way back from Mexico to find prime breeding grounds. It’s a risky game for a small bird, but Yellow-rumpeds are just physically and behaviorally robust enough to gamble.
Having grown up in Seattle, it’s seemed to me that Yellow-rumped Warblers are wintering in larger numbers in our area than they used to. To see if this was correct, I turned to data from the largest and longest running citizen science program in the world, the Chirstmas Bird Count, to check the data from the past 40 years.
Though the number of observers participating in our area has increased markedly, it’s clear that more Yellow-rumpeds are around during our winters. With 100 observers in 1977, there were only 4 individuals recorded for the entire Seattle area. In 2017 with 216 observers, 172 individuals were recorded. Interestingly, there’s also been very low counts in certain years, even recently. Possibly this is due to environmental conditions that made winter in Seattle untenable. Why they’re sticking around longer in Seattle is anyone’s guess, but I’d hazard that our winters aren’t as harsh as they used to be.
Although they’re much drabber in Winter, I love hearing the distinctive chip note of a Yellow-rumped Warbler on a dreary day. They remind me that winter if not forever. They are also amusing to watch because of their active foraging style, hopping for branch to branch, sallying forth to catch an insect, spreading their beautifully spotted tail in the process. They keep their “yellow-rump” all winter, a nice hint of yellow during the gray.
Keep your ears and ears open and maybe you’ll start noticing them working the tops of trees down Broadway or 15th, chipping and flitting about while we go about our days below.