Bird of the Month: Yellow-rumped Warbler
Butter butts
Yes, their nickname is butter butts. Why? Because there is a small patch of yellow on their rumps that is obvious as they flit around in the mid-story of trees (above the ground but below the larger canopy). Go ahead and giggle. We do.
Within the Yellow-rumped Warbler species there are two subspecies: Audubon's, which occur in western North America and Myrtle, which occur in the east. They used to be separate species but were lumped together as one back in the 1970s. Although they look similar, they have enough plumage variation to be identified as one or the other. But no matter which "outfit" they're wearing, there is always that distinct yellow patch on the rump.
The subspecies Myrtle is the one typically found in our area. And it's the only warbler that can be found here in winter, much to the amazement of new birders. A warbler in winter? But how? Although they nest in the northern boreal forest, they come "south" for the winter and what makes our climate acceptable to them is the native shrub northern bayberry (Myrica pensylvanica), which grows in abundance at Presque Isle State Park.
Like other warblers, Yellow-rumps feed primarily on insects in the breeding season, but their winter diet includes a substantial amount of fruit. The species' ability to digest the waxes in bayberries make it unique among warblers and allows them to winter in our area (and as far north as Nova Scotia).
To find them, look for bayberry stands on the park and then use your eyes, since Yellow-rumps are not known for singing on the wintering grounds (although you may hear a few low, flat "chep" calls).
A winter bird walk at Presque Isle is often dominated by waterfowl species, but butter butts are the bright yellow spots in an otherwise dull winter landscape. And when you find one, point and say "butter butt!" It's a good way to dispel any seasonal gloom.
Mary Birdsong is the lead shorebird monitor for Erie Bird Observatory. Learn more at eriebirdobservatory.org. Mary can be reached at mbirdsong@eriereader.com
