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Mercury levels threaten Bicknell’s Thrush

The rare mellifluous sound in the woods makes bird watchers look around to spot the location of Bicknell’s Thrush. Indeed, citing of the bird is done more by its song at high elevations unlike other birds by the researchers. The smaller and slimmer Bicknell’s Thrush (Catharus bicknelli) is considered a cousin of the American Robin that is seen commonly. On the other, Bicknell’s Thrush with a brown back and wings, chestnut tail, and speckled throat is spotted very rarely.

The rare Bicknell’s Thrush is threatened by the mercury levels, a recent report of the Vermont Institute of Natural Science points out. Though Bicknell’s Thrush is not declared as endangered species till now, the rare bird breeds only in scrubby boreal forests that are located on top of mountains in places like New Hampshire, New York, Maine, Vermont and East Canada.

The blood samples of the bird collected from different locations of habitat – summer and winter - points to the presence of mercury in all of them. Though mercury is found to be present in these birds, it is not confirmed whether they reached the alarming levels as yet or not. In fact, this is a surprising find for the bird watchers. Already, documented evidence pertaining to loons and other water birds reveal that these species are facing neurological and other reproductive problems as a result of high mercury levels from eating fish. The mercury levels have moved up the food chain from soil to insects to birds on highest peaks in mountains. Much of the mercury pollution is blamed on the coal-fired power plants in the Midwest.

Added to this, Bicknell’s Thrush habitat is threatened by global warming. The balsam fir forests, which are frequented by these birds, are increasingly coming under the impact of climate change. On the other hand, the bird’s winter habitat in Caribbean Island of Hispaniola is threatened by development works. To protect the bird’s habitat, the government has come forward to scale down plans to expand the ski center on Whiteface.

The study undertaken by the Institute for the last five years has brought out another interesting fact - a 7 percent decline in Bicknell’s Thrush population over the period. Though the loss of habitat is contained with the stoppage of tree-cutting atop Adirondack’s hills, communications towers and wind mills are posing problem to the rare songbird. Nearly, 70,000 acres in Adirondacks are found to be perfect places that support breeding populations of Bicknell’s Thrush.

Mistaken identity?

While Bicknell’s Thrush is known for its lilting tunes, the identification of the bird as a subspecies of widespread Grey-Cheeked Thrush is proved wrong by a taxonomist. Till then, no special efforts are made to study the habitat or conservation of the rare songbird. The study of Bicknell’s Thrush has brought out the fact that males outnumber females by 2 to 1 and, males and females mate with different partners. The total population of the rare bird is estimated between 20,000 and 40,000.

Since the habitat of the rare bird is on the hilltops, conservation of trees on the mountain tops spread across its habitat zone assumes importance. The nesting places of the bird in winter and summer require conservation efforts to save it from extinction. Though the impact of global warming on the Bicknell’s Thrush is not fully evaluated as yet, the loss of habitat is proving to be a major concern among the bird watchers. The development of new ski tracks, in particular the Tree Island Pod may cause some disturbance to the natural habitat of the rare songbird, it is said.

However, as the study on the bird and its habitat is very recent, a large database on the impact of development is essential for conservation efforts. The location of trails along the natural terrain with tree cover is not fully estimated about its impact on the Bicknell’s Thrush. Also, the new addition to ski areas should not be separated from the existing Bicknell’s Thrush habitat area as otherwise this will severely impact the breeding grounds of the rare bird.

Chandra Sekhar

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