On Warblers

Spring begins with song, the dawn chorus warming up with a few notes in March and growing into full avian voice by May. Some of our best singers are the wood warblers, migratory songbirds, typically weighing under half an ounce, that winter from South America to the Caribbean and return northward to mate, nest, and raise young each year.

Western Pennsylvania is a hotspot for warbler watching — and listening — with a variety of habitat available for migratory stopovers and breeding. Among the warblers are some of the most colorful songsters of the bird world.

Black-throated Green Warblers are early arrivals, winging their way from Columbia and Venezuela. As soon as it’s warm enough for insects here, usually the first weeks of April, Black-throated Green males first appear to glean these pickings from among branches and budding leaves. Females follow soon after. Visit Frick Park or some of its suburban equivalents, and you’ll hear the male’s high trill, zee zee zee zoo zee (in most bird species, it’s the male that sings to discriminating females or to wary male rivals). Binoculars will help you locate the source of the music. The male, a bit smaller than a sparrow, is olive green across the crown and shoulders, yellow on the face, and dipped in inky black from beak to chest. Its wings and belly are a mix of blacks, whites, and grays. Females, as in most bird species, are far less showy. Male or female, warblers almost never come to bird feeders, so if you’re unfamiliar with these neotropical migrants, seek them out before the leaves of spring hide them and their companions.

Most male birds returning in spring sport their brightest colors of the year, with gaudy plumage complementing vocal repertoires. For proof, look no further than the fiery orange and yellow Blackburnian Warbler, which arrives in late April and early May. Nicknamed “firethroat,” this beauty hopscotches from the Andes of Peru to Costa Rica, across the Gulf of Mexico and northward to Squirrel Hill and beyond as it seeks good breeding territory. Seeing a bright male in migration is a highlight of any morning bird walk, but hearing it, zip ti-ti tsee-e-e-e-e confirms that spring has arrived. Warblers like the Blackburnian migrate in response to the abundance of light, the readiness of breeding grounds farther north and the availability of food along the way. Blackburnians favor caterpillars and dine in the treetops. Other warblers forage for slightly different morsels and typically can be found at varying heights. This vertical segregation allows numbers of species that eat the same foods room at the table. In migration, though, anything is possible, so keen ears and eyes reward the attentive birder in spring.

To see warblers this season, take a free bird walk with the Audubon Society of Western Pennsylvania, www.aswp.org or 412-963-6100. The Three Rivers Birding Club hosts regular meetings and free local field trips, www.3rbc.org. Powdermill Avian Research Center of the Carnegie Museum of Natural History in Rector, about an hour east of Pittsburgh, is well worth a visit to see trained ornithologists study living birds in the hand, www.powdermill.org.