Friday, June 27, 2003
Wood Thrush Hylocichla mustelina
Voice: One of our loveliest singers. Song is flute-like, made up of at least four short phrases, usually with pauses between and repeated in the same order. Sometimes described as Eohlay, aholee, ahleelee, but there is considerable variation among singers. After listening to particular birds from May through July, you can tell if they come back the following year. One of three Wood Thrushes singing in our neighborhood off Concord Street and Bingham Road this May has returned for at least his fourth spring. Although most of the singing is done by the male, the female is known to give a short version of the song near the nest.
Calls, given by both sexes, include a loud, fast Whit-whit-whit-whit (my father used to say that this call sounded as if the bird had a mouth full of water), a softer Trrrrrr-trrrrrr, and a high, single-note call that sounds like Eng! (something like a Veery but higher).
Places to listen for Wood Thrushes in Carlisle include the Towle Land, across Curve Street from the Cranberry Bog, and the Estabrook Woods.
Nesting: Wood Thrushes are most vocal early in the season when males set up territories. They chase other males out of their territory (often two acres or more in residential areas), and also, initially, the female. But she doesn't go away, because she's attracted to his lush singing. Eventually, he gives up and just follows her around.
The female builds a robin-like nest of mud and rootlets, often with a piece of white paper or plastic in it. A nest I saw several years ago in Concord had part of a Stop-and-Shop bag woven into it.
Nesting habitat can be either deciduous or mixed woods, usually near a swampy area. Wood Thrushes often choose wooded residential areas for nesting, even though raising young is more likely to succeed deep in a large forest. A thrush nest in a yew tree next to our long driveway was overturned and the eggs eaten, probably by a raccoon. Blue jays and other predators also eat bird eggs and young, but usually don't dislodge the nest.
Food: Wood thrushes eat insects and other small invertebrates such as spiders, earthworms, and snails. They also consume berries, especially during September, when they are putting on calories for their long trip to wintering grounds in Central America. Favorite fall fruits include dogwood, pokeweed, and viburnum berries.
Conservation: Although still fairly common in Massachusetts, the Wood Thrush has been declining for many years, and has been placed on the Watch List of the American Bird Conservancy. This list is intended to identify birds before they reach the endangered status.
Wood Thrushes are affected by a lack of quality breeding habitat (see above, and the article on the Ovenbird in the June 6 Mosquito). A recent study has shown that acid rain is contributing to their decline in many forests. Acid rain leaches calcium out of the soil, leading to the disappearance of such calcium-rich foods as snail shells. Without ample calcium in their diet, female thrushes cannot produce enough viable eggs to keep the population going.
References: Sibley Guide to Bird Life and Behavior, Stokes Guide to Bird Behavior Vol.II, Life Histories of North American Thrushes, Kinglets, and Their Allies by A.C. Bent,
Birdscope, newsletter of the Cornell Lab of Ornithology, Autumn 2002.
© 2003 The Carlisle Mosquito