Sunday, December 12, 2010

The yellow-rumped warbler

Dendroica coronata, the yellow-rumped warbler.

With ornithological practicality, the little warbler with a bright patch of yellow feathers at the base of its tail is called the yellow-rumped warbler. It is one of a group of small, primarily insect-eating birds called the wood warblers. We mainly see wood warblers passing through New York City in spring on their way to northern breeding grounds or heading south in autumn. 

They are about five inches long, stripy brown, weigh less than half an ounce, and have patches of yellow on rump and sides. In summer they are brighter and have white patches on the wings and face. 

Some yellow-rumped warblers spend the winter in New York. (Others can be found in winter throughout the northeast, across the southern half of North America, in Mexico, and throughout Central America.) You might see yellow-rumped warblers in places as varied as forest edges, coastal shrubs, or backyards and parks. 

The one pictured here was foraging about a month ago at Alley Pond Park in Queens in New York City -- at the nexus of the Cross Island Parkway, the Grand Central Parkway, and the Long Island Expressway.  Yellow-rumped warblers are clearly not troubled by traffic! This bird might have been evaluating the neighborhood as a winter retreat, or just stopping off to eat something on its way south. It may in fact be visiting a feeder in Miami right now, or even feasting on tropical caterpillars in Guatemala. 

But if it stayed its diet would change from mostly insects to mostly fruit. The yellow-rumped's digestive system is even uniquely adapted to allow it to eat bay berries and wax myrtle berries. Not surprisingly, one of its other common names is the myrtle warbler. 

Yellow-rumped warblers are famously clever foragers. They flit from tree to tree, gleaning insects. They pick insects out of spider webs and off water surfaces. The one in these pictures was taking advantage of another bird's work. See the rows of holes in the tree? They were made by a yellow-bellied sapsucker. The sapsucker is a kind of woodpecker that specializes in drilling holes in trees, eating some of the live cells, and licking up tree sap with its bill inserted in the hole. Sapsuckers always make their holes in neat rows like those shown in the photos. Insects get accidentally trapped in the sticky sap at the holes. Other kinds of birds visit sapsucker holes to snack on sap and sticky insects. 

Oh and bird watchers call yellow-rumped/myrtle warblers butter butts

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