Wood-warblers 101: Treasures in the Trees

by Simon Housner with photos from the VIREO Collection

Now that spring migration is in full swing, there is a family of birds particularly popular among avid birders to look for… wood-warblers! These minuscule birds fascinate us with their unwavering energy, mesmerizing colors, and wondrous warbling. There are 54 species of wood-warblers that regularly visit North America, and over 30 of them can be found in the greater Philadelphia area during peak migration this May. Passionate bird watchers gladly endure considerable neck-aches to peer into the treetops for just a glimpse, for the most colorful species are found in the canopy, while some more subtle beauties can be seen nearer to the ground. Here’s five eye-catching warblers you are likely to see if you look up and focus your binoculars on the smallest and fastest moving birds that you can find:

Yellow-rumped Warbler

Yellow-rumped warbler. Dendroica coronata. Jamaica Bay, Gateway. A male yellow-rumped warbler feeding on poison ivy berries during spring migration.
Yellow-rumped warbler. Dendroica coronata. Jamaica Bay, Gateway. A male yellow-rumped warbler feeding on poison ivy berries during spring migration.

One of the most commonly observed species, Yellow-rumped Warblers are usually found foraging in sizable numbers and can be recognized by their namesake yellow rump patch, which has earned them the nickname of “butter butt.” Geographically split into two subspecies, the “Myrtle” subspecies inhabits eastern North America while the “Audubon’s” variety is found in the West. Yellow-rumped Warblers consume a wide variety of insects during breeding season and berries in the wintertime. Due to their unique ability to digest inedible berries from wax myrtle, bayberry, and poison ivy, they are able to winter much farther north than other wood-warbler species.

Black-throated Blue Warbler

Black-throated Blue Warbler (Dendroica caerulescens) perched on a branch in Eastern Ontario, Canada.
Black-throated Blue Warbler (Dendroica caerulescens) perched on a branch in Eastern Ontario, Canada.

Black-throated Blue Warblers regularly spend winter vacation in Florida and the Caribbean. When spring migration begins, they fly by night for eastern North America- a journey of roughly 1,300 miles – and drop in to rest and forage for the day at first light. Since male and female Black-throated Blue Warblers are dramatically different in appearance, or sexually dimorphic, they were originally believed to be two separate species. Early American ornithologists first dubbed the females “Pine Swamp Warblers.” Eventually the error was discovered and Black-throated Blue female warblers became known as “Audubon’s Extra Warbler” since John James Audubon had depicted them as their own species in his monumental work Birds of America.

Yellow Warbler

Jamaica Bay 15.4 mb
Yellow warbler

To the casual observer, the Yellow Warbler may resemble a tiny golden orb floating among the treetops. Readily distinguished with their signature song, males have rich reddish chestnut streaks on their chest, which the duller females lack. Yellow Warblers are another long distance migrant that navigate over the featureless Gulf of Mexico by starlight on their way to their breeding grounds throughout North America. Brown-headed Cowbirds, a brood parasite that lays its eggs in the nest of another species in order to trick them into raising their young, often choose Yellow Warbler nests as a host. If the nesting warblers recognize the intruder, they may construct a new nest right above the entire infected clutch of eggs. Nests like this have been discovered with 5 or more layers!

Black and White Warbler

Black-and-white Warbler c22-38-051
Black and white warbler

Black-and-white Warblers are early migrant warblers that have been arriving in the Philadelphia area for the past several weeks and continue to throughout May. With exceptionally long claws on the rear of their feet, they possess a remarkable ability to cling to trees with the agility of a woodpecker or nuthatch. Black-and-white Warblers favor deciduous and mixed forests, so be sure to look for these strikingly patterned warblers creeping along tree trunks and limbs in search of an insect meal.

Chestnut-sided Warbler

Glenn Bartley www.glennbartley.com
Chestnut-sided Warbler

Chestnut-sided Warblers winter from southern Mexico to the West Indies and the month of May finds them arriving in the Philadelphia area. Another insectivorous bird, this warbler species has two distinctly different songs, only one of which is accented near the end and used by males to attract the mates. The song lacking the accent is mainly used to establish and defend territories and it gradually replaces the accented version once nesting and raising young begins. Some DNA studies suggest Chestnut-sided Warblers are closely related to Yellow Warblers and both species also exhibit similar vocalizations.

Wood-warblers can be a bit of a challenge to see – most are just about 5 inches from the tip of their beak to the tip of their tail – and they rarely stay still for more than a few seconds. Listen for their short, sweet songs and trills while watching for quick flittering movements and get your binoculars on them fast.

Are you up to the challenge and wondering where you might get a chance to these five species this May? All five have been found at John Heinz National Wildlife Refuge just this past week.

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