Birds of Curtis Park: Yellow-rumped warbler usually seen in motion hunting for insects

During the winter, the only warbler you are likely to see in the neighborhood is the yellow-rumped warbler.

The first thing that you notice about this bird is splotches of bright yellow. These splotches vary in intensity and scope with season, gender, and sub-species; however, there is always a characteristic bright yellow patch on the lower back that gives it the name yellow-rump, or more informally, “butter butt.”

The males can be somewhat drab in winter, but become far more colorful as the breeding season approaches.

Upper right, the yellow throat is an Audubon subspecies and the other two with white throats are Myrtle subspecies. Photos/Dan Murphy

The yellow-rump warbler used to be divided into two species – Audubon and Myrtle. The Audubons predominate in the West and Myrtles in the East, though Myrtles are not rare here. As a result of evidence of hybridization, as well as genetic similarities, it is now classed as one species with two sub-species in the United States. The chief visual distinction is the Audubon has a yellow throat and the Myrtle a white throat with a dark face outlined in white.

For most of the summer, yellowrump warblers disappear locally. This is because they are specialized to a conifer breeding habitat and migrate north and to the mountains for this critical period.

As the thin pointy beak indicates, the yellow-rump warbler feeds mostly on insects. It catches them in flight or by foliage-gleaning. It is usually seen in motion, hunting, with brief pauses. In winter it eats more berries, including waxy fruit that other warblers cannot digest, which allows it to winter as far north as Nova Scotia.

A yellow-rump is 5.5 inches tail tip to beak tip and weighs about 12 grams. Local bluebirds and sparrows are an inch or an inch and a half longer, but are twice as heavy or more.

The lifespan of a yellow-rump warbler is seven years.

Written by Dan Murphy and posted on Wednesday, March 10th, 2021

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