Bicknell's Threats Stretch Beyond the ADK

Few people will ever see or hear this remarkable bird before it goes extinct by 2100. Although its numbers are not in immediate peril, this relative of the American Robin, Wood Thrush, and Eastern Bluebird is plagued with human-induced, chronic environmental health problems that show no signs of disappearing.
Bicknell’s thrush probably exploited the narrow band of boreal-like conditions just south of the ice pack during the peak of glaciation 18-25,000 years ago in North America. As the climate warmed and the glaciers melted, breeding populations of Bicknell’s thrush followed the spruce forest northward each year during spring migration. This forest continued their march northward and some jumped on the escalator delivering them to higher altitudes in the Catskills and Adirondacks of New York, the White/Green Mountains of Vermont, and the mountain ridges of Maine. Some populations became established in Maine and southeastern Canada. Today breeding populations are generally found in suitable habitat above 3500 feet in the ADK.
It is no longer a secret that the climate is warming. Forest communities in the Adirondacks continue to seek out the ground where the appropriate climate for their survival, growth, and reproduction. This means that the spruce fir forests are moving up peaks in the northeast. As the forest migrates to new heights, their total area declines as one might expect from simple geometric analysis on pinnacles. The rules are simple: higher forest, smaller habitat, fewer birds, and greater risk of extinction. Although the Adrondack mountains are growing at a blistering rate of 3 mm per year, global warming and climate change have and will continue to outpace mountain growth. Thus, sometime in the next century the optimal climate for spruce/fir forests will be gone from most of the northeastern United States.
Climate change brings the nails to the coffin on Bicknell’s inevitable death, but it doesn’t seal its fate. Some believe there is still time to help the species. Population numbers are still high. Perhaps populations can adapt to the rising deciduous forests or migrate further north. Perhaps, the climate change nail will rust before its time.
Other nails exist and are currently being driven into Bicknell’s coffin. The industrial revolution of the 19th and 20th century has brought about atmospheric and ecosystem changes that have had a greater impact in the Adirondacks and northeastern United States more so than anywhere else in the country. Coal burning powerplants in the Midwest facilitated this countries growth and industrial boom. Smokestacks were built high to carry the coal emissions far away in the overhead airstream. As sulfates, mercury, and nitrates dissolved in atmospheric water vapor the pH of the water becomes more acidic. Eventually these pollutants fall over the northeastern mountain peaks in snow and rain precipitation.
Until recently the atmospheric pollutants in the Adirondacks seemed to affect lake chemistry the most. Acidified lakes experienced a shift in types of plankton and lost fish species. Many western Adirondack species are now left with the legacy of no fish and low pH from acid precipitation. Aquatic bacteria in the ponds and lakes converted mercury deposition to the toxic methyl mercury. This in turn has bioaccumulated and magnified in fish and higher order predators such as loons and eagles. In the mountains, acid precipitation altered soil chemistry by leaching important cations and increasing the availability of aluminum in the soil. Aquatic bacteria in the ponds and lakes converted mercury deposition to the toxic methyl mercury. This in turn has bioaccumulated and magnified in fish and higher order predators such as loons and eagles. Spruces seemed to be most affected by acid precipitation and exhibit excessive winter kill of yearling needles. To Bicknell’s thrush all of the problems associated with acid precipitation appeared to be downhill and out of reach.
Then in 2005, Rimmer, McFarland, Evers and colleagues reported that Bicknell’s thrush blood serum contained levels of mercury and methyl mercury that were usually associated with wetland bird species such as northern waterthrush and common loon. These results surprised the researchers and ecotoxicologists because a montane bird species with a diet based on terrestrial invertebrates shouldn’t experience methyl mercury contamination. The results implicated two potential sources of mercury contamination in Bicknell’s territory. On breeding grounds, a previously unknown mechanism of terrestrial conversion of methylmercury in leaf litter followed by bioaccumulation in soil invertebrates. Methylmercury may then biomagnify across the invertebrate food chain and into Bicknell’s diet. A second source of methylmercury accumulation now appears likely on Bicknell’s winter habitat on the island of Hispaniola. The concern for Bicknell’;s thrush and other exposed songbirds is that methylmercury toxicity may lead to behavioral problems and reproductive failures as has been observed in Adirondack loons.
If the two nails, global climate change and mercury poisoning, don’t seal the coffin, then perhaps the third problem of winter habitat degradation will. Bicknell’s thrush spends its winter in montane forests on the island of Hispaniola. This island is divided between two nations of the Dominican Republic and Haiti. Poverty, government instability, and excessive human population have resulted in intensive land use and deforestation in Haiti. Wood is the staple energy and heating source for Haitians. Periodic changes in government environmental practices and philosophies in the Dominican Republic keep Bicknell’s habitat walking a thin thread between hope and gloom. In short, Bicknell’s thrush has troubles on both ends of its migration.
The recent quest for clean renewable energy has developed new concerns for montane birds in the northeastern United States. Wind farms have been proposed in prime Bicknell’s habitat on mountain ridges in Maine and Gore Mountain in New York. Environmentalist have temporarily beaten down these proposals, but as the price of oil continues to rise and humans become more desperate for clean energy the halt may only be temporary. No one knows whether wind farms will have a negative impact on Bicknell’s thrush, but it is certainly another encroachment on a species in decline.
Only time will tell if these concerns err on the side of extreme pessimism. Biology and evolution has clever solutions to a multitude of problems. Perhaps Bicknell’s thrush will evolve a strategy to utilize breeding habitats further north or adapt to new plant communities on the rise in the Adirondacks. Both scenario present Bicknell’s thrush with new social struggles and competitive challenges that will need to be solved.