The wood thrush sings a haunting song, “Ee-oh-lay.” Just three syllables, it’s a brief, ethereal mix of bouncing notes and plaintive, romantic flutings. I have heard the males sing from brushy patches of suburban scrub in the late spring and from deep in the summer woods. Their notes are almost elven, with something beckoning and magical, though the bird itself is rarely seen.
Wood thrushes are akin in size to small, bulky robins and are found in the same scientific family. With orangey heads, rufous-brown backs, and white, spotted chests and bellies, they scramble along the forest floor, mostly looking for invertebrates to munch, like ants, beetles, and spiders. In summer, they add small fruits to their repast: blueberry, elderberry, holly fruit, dogwood berries and other treats that would hardly capture a human’s attention, but for this eight-inch bird, the foraged bounty is a sweet enhancement to an otherwise buggy diet.
Summer is breeding season, and wood thrushes prepare for parenthood in what might be considered a typical avian way: they shape a four- to six-inch nest, round and made from grass, leaves, moss, and stems mixed with mud and molded by the female into a cozy cradle that will hold three to four greenish-blue eggs. Incubation and infancy are each about two weeks long, and then the fledglings fly the nest. Sometimes, there is a second brood.
Wood thrushes face one big problem: cowbirds. This nondescript black and brown species likes those same nests. The cowbirds push into edge habitats, forest margins that have been disturbed, making the woods more susceptible to incursions and disturbances. The cowbirds dump a few eggs into the exposed nests of wood thrushes, hoping that the unsuspecting songsters will raise their kids instead. Called nest parasitism, this strategy is great for the roaming cowbirds and lousy for the wood thrushes, who do the parental duties only to have their own offspring literally pushed out of the nest by the babies of these greedy, aggressive interlopers.
Along with the calcium-depleting effects of acid rain, which makes eggshell production a challenge, forest fragmentation is a presumed contributor to the precipitous decline of wood thrushes, which have nationally seen 50 percent of their numbers disappear since the mid-1960s. In Pennsylvania, though they are widespread, their population has declined from about 1.2 million males to some 660,000, about 8 percent of the global population, as detailed in the last statewide breeding bird atlas.
If you want to improve your observation and attention skills, try birding by ear. Merlin Bird ID is a free app from the Cornell Lab of Ornithology that helps match birdsong and singer. A walk in the woods to listen for the wood thrush is a fun way to test a new skill, get outside, and enjoy the sounds of spring and summer. Good listening!