Bicknell’s thrush nest in mountain-top evergreen forests in Vermont, areas that are shrinking due to global warming. Photo: © T.B. Ryder
Watch a video of a Bicknell’s thrush feeding her young.
Bicknell’s thrush has one of the most restricted breeding ranges of any North American bird, nesting primarily in stunted spruce-fir forests found at or near the highest elevations of mountains in Vermont and other New England states. These mountain tops are like a chain of islands separated by a sea of habitat that is unsuitable for this species.
As the climate warms and precipitation patterns change, deciduous trees – those that shed their leaves in the fall – are likely to become more prevalent in higher elevations, shrinking the size of the mountain-top evergreen conifer forests that are home to the Bicknell's thrush.
This is just one of many challenges that climate change poses for the rare bird.
Another potential threat is a mismatch between the arrival time in spring of Bicknell’s thrush and other birds, which is regulated by day length, and the abundance of insect prey, linked to temperature. If the peak food supply for birds comes earlier due to warmer spring temperatures, late arriving birds may lay fewer eggs and produce offspring that have less chance of reaching adulthood.
The red squirrel, which also lives in the mountain-top forests, also presents a danger. The squirrels feed mainly on spruce and fir cones, but will also raid the nests of Bicknell’s thrush to feed on eggs and young birds.