I don’t have to leave this planet to hear the music of the spheres. Surely, listening to wood thrushes singing is as ethereal an experience as any mortal can hope for on earth. Many evenings, when I step outside, wood thrush song envelops me and it seems as if all the world’s wood thrushes are singing on our mountain.
Most years I can count on the first wood thrush song between April 30 and May 5 and the absolute last wood thrush song near the end of July. But, in 1997, I heard a wood thrush singing on August 5. The following summer a wood thrush broke that record by singing for a few brief moments at dawn on August 12. Then, last summer, the final date was August 3.
No matter when it happens, though, I listen with an impending sense of loss throughout July. Once again, time is running out, and I have not yet had my fill of wood thrush music. They are with us too short a time, singing like what I imagine angels would sound like, then leaving me bereft the rest of the year. Yet, I wonder if I would be as enchanted by wood thrush song if I heard it all year long or if familiarity would breed, if not contempt, inattention?
Of course, what is exquisite music to me is serious business for wood thrushes. As soon as the males return from their fall and winter homes in the lowland tropical forests from southern Mexico to Panama, they sing loudly from elevated, exposed perches, intent on attracting females and defending their one-quarter to two-acre territories from other males.
Song duels between males, called “countersinging” by ornithologists, in which two males come to within ten yards of each other and alternate songs, are common during territorial disputes. When females arrive, males chase them and sing aggressively. Each male tries to attract a female to settle in his territory. Once he does so, the male sings in lower, hidden sites.
But there are singers and then there are the outstanding virtuosos. The flutelike ee-oh-lay is learned from adult wood thrush males during the fledgling stage. But both his mostly inaudible, short note introduction and trill-like ending are either innate or invented. Each part of his song has several variations and every male has his own repertoire. For instance, one Ohio male sang 18 patterns out of 90 possible ones based on his variations, according to a study conducted by D.J. Borror and C.R. Reese entitled “Vocal gymnastics in Wood Thrush Songs” back in the early 1950s. Another study of 115 wood thrush songs by Aretas Saunders showed ranges as wide as two octaves with the average thrush’s range slightly over an octave.
I well remember the organlike tones of a particularly varied wood thrush song I listened to one evening in a darkening wood. To my ears, the singer seemed to be singing for the pure joy of it. Whether birds have a musical sense is still debatable among scientists, but there is no doubt that they use musical devices, such as crescendo and diminuendo, as well as complex musical phrases, and that they continue to develop their songs long after they have mated and established a territory. In fact, after a lull in their singing in early June, when they are busy feeding nestlings, wood thrushes begin singing again in July with almost as much intensity as in May, and I often hear them countersinging.
One July evening, along the Short Circuit Trail, I counted three wood thrushes singing at the same time, each song coming from a different direction. On other summer evenings my walks take me from one singing wood thrush to another as I move in and out of a succession of thrush territories. Long after I return home, my ears ring with their tremulous echoes and vibratos and, like Henry David Thoreau, the wood thrush’s song “touches a depth in me which no other bird’s song does…it lifts and exhilarates me.” The wood thrush, he writes, is the “minstrel of the woods,” the “master of a finer-toned instrument…a Shakespeare among birds…”
Also known as “bellbird,” “song thrush,” and “swamp angel,” the wood thrush’s genus name Hylocichla is Greek for “wood thrush” while its species name mustelina means “weasel-like” in Latin, referring to its tawny head, wings and back which are supposed to resemble the color of a weasel. Otherwise, the wood thrush has a white breast and belly, liberally sprinkled with larger round or oval black spots.
The nicknames, “swamp robin” and “wood robin,” refer to its membership in the Thrush family along with other outstanding singers such as the American robin. Like robins, wood thrushes forage on the ground by hopping and then pausing to search. They also toss leaves aside and probe the earth with their bills. Once a male attracts a female, they engage in sexual chasing in which the female leads the way during silent, circular flights, interspersed by perching together. Copulation occurs on branches and most pairs are monogamous through the nesting season, which includes the raising of two broods. A small percentage nest with the same mate a second season. One female was unusually loyal, mating with the same male five years in a row and then with another male for three years.
The female chooses the nest site with some input from the male who indicates his preference by “pit-pit” calls and by bringing nesting material to the spot even though the female does the nest-building. It takes three to six days to fashion the cup-shaped nest anchored in a hidden tree crotch or shrub or on a branch five to 20 feet from the ground. Resembling a robin’s nest in shape, it is distinguished by a lining of rootlets and often has a piece of paper or white cloth hanging from the base. The ones I have found here incorporate a piece of plastic from the old farm dump instead of the cloth or paper. During the 1970s, when we had a large population of wood thrushes, I once found three nests within a couple hundred feet constructed in mountain laurel shrubs.
The female usually lays three to four, blue-green eggs, and incubates them from 12 to 13 days while the male perches on trees 20 to 30 yards from the nest and feeds, sings, or preens. He also guards the nest by standing on or next to the nest rim and sometimes singing while the female forages. He occasionally brings her food and freezes if an intruder approaches the nest.
Once the eggs hatch, the male does two-thirds of the feeding of nestlings until they fledge at 12 to 15 days of age. Then the parents divide up the brood and continue feeding them until they become independent and leave their parents’ territory at the age of 21 to 31 days. By then the female has begun laying her second clutch of eggs.
Since the 1970s, wood thrush numbers have fallen, both on their breeding and wintering grounds. Researchers in the Midwest pointed to excessive parasitism by brown-headed cowbirds, which lay their eggs in other birds’ nests for them to raise. The cowbirds grow faster and are more aggressive than the nest-builder’s young so usually the host species raises less of its own offspring. But in Pennsylvania, Jeffrey Hoover and Margaret Brittingham found that despite a nine-percent cowbird parasitism rate on wood thrush nests, there were no nest failures.
On the other hand, in a study done at Hawk Mountain Sanctuary by Hoover, Brittingham and Laurie Goodrich in 1990, fragmented forest habitat was the more critical issue. Wood thrush nests in small forest patches were more heavily preyed upon than those in larger forests.
Researchers have found that the primary predators on wood thrush eggs, nestlings, and/or fledglings are blue jays, common grackles, American crows, gray and southern flying squirrels, chipmunks, least weasels, white-footed mice, black rat snakes, sharp-shinned hawks, raccoons and pet and feral cats. But large, mature forests with well-developed understories provide better protection from predators.
Such forests are also an excellent source of the beetles, ants, caterpillars, moths, flies, bugs, spiders, sow bugs, snails, and earthworms that wood thrushes eat in the summer and feed their young. Later, after the fledglings have dispersed, and during migration, wood thrushes switch to fruits. Then they prefer more open areas that support fruit-bearing shrubs, vines and trees such as spicebush, fox grapes, blueberry, blackberry, mulberry, holly, elderberry, Virginia creeper, pokeweed, dogwood, black cherry and black gum trees.
Here in Pennsylvania the United States Fish and Wildlife Service’s annual Breeding Bird Survey recorded its highest number of wood thrushes per route in 1977 (22). Since then there has been a slow downward trend, but during the Pennsylvania breeding bird atlasing project–from 1983 to 1990–atlas volunteers found wood thrushes throughout the state in every county. Pennsylvania also holds the record for the longest-lived wood thrush–eight years and ten months old.
As long as suitable woodland habitat remains for wood thrushes here, along their migration route, and on their wintering grounds, wood thrushes will survive. As Thoreau wrote on July 5, 1952, “The thrush alone declares the immortal wealth and vigor that is in the forest…Whenever a man hears it, he is young, and Nature is in her Spring.”