This week’s Bird of the Week, compliments of the Weminuche Audubon Society and Audubon Rockies, is the yellow-rumped warbler.
In our area, by the end of September, warbler season is for the most part coming to an end. Typically by then, these colorful, active, insectivorous birds will have moved on to warmer climes for the winter. The yellow-rumped, however, will be around for a while, migrating later in fall than others. It is sometimes even spotted here as late as December.
This is one of the most widespread and well-known warblers in North America, breeding in coniferous and mixed forests. One group, the “Audubon’s” type, breeds primarily in the mountains of the west and into British Columbia. The “Myrtle” type with a white throat breeds primarily in eastern states and across Canada to Alaska. A short- to medium-distance migrant, yellow-rumped warblers are found in central and southeastern states, and are abundant along the Atlantic coast in winter.
An adaptation in the digestive system of this warbler allows it to digest the waxy coverings of the fruits of the bayberry and wax myrtle, which are plentiful along the Atlantic coast and provide a winter food source. Other fruits commonly eaten in fall and winter include those of juniper trees, poison ivy, poison oak, grapes and dogwood.
In summer this warbler flits about in the canopies of conifers gleaning insects from the trunks, branches and needles of trees. It will also perch on outer limbs and fly out to grab insects from the air.
A yellow-colored rump is diagnostic for these birds and has earned them the affectionate name butterbutt. The Audubon’s type, most common here, also shows patches of yellow on the crown, throat and sides. Breeding males have blue-gray backs with black streaks. Females and winter birds are more muted and brownish.
According to the American Bird Conservancy, over 60 percent of the yellow-rumped warbler population breeds in the boreal forests of Canada, where wildfires this summer have affected air quality and burned millions of acres of breeding habitat. While fire has always been a natural part of the landscape, it is unknown how bird populations will be impacted by this year’s massive fires.
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