The State of Hermit Thrushes
Northeastern United States: Increasing in New York, declining elsewhere
Hermit Thrush are relatively uncommon in the montane forests surveyed as part of Mountain Birdwatch. By comparison, a visitor to the spruce-fir zone is likely to encounter approximately twice as many Bicknell’s Thrush as Hermit Thrush. The estimated local abundance of Hermit Thrush around Mountain Birdwatch sampling stations, in the figure below, paint an interesting picture. What’s even more Numbers of Hermit Thrush were clearly on the rise from 2011 to 2014, but then the population suddenly declined (by nearly 50%) where it has remained since 2015. What’s even more interesting? Look at the table of regional trends below. Populations of Hermit Thrush (in the spruce-fir zone) are exploding in New York and sharply declining in Vermont, New Hampshire, and Maine. These declines follow an obvious longitudinal pattern: the declines become increasingly steeper in the western part of our region.
|Region||Mean annual trend (%)||95% credible interval|
|All regions combined||-4.00||(-6.14, -1.68)|
|New York (state)||7.84||(3.74, 12.01)|
|New York (Catskills)||8.49||(3.66, 13.04)|
|New York (Adirondacks)||7.57||(2.15, 13.90)|
|New Hampshire||-9.51||(-14.24, -4.78)|
Those trends for the spruce-fir zone in Maine (-13% per year) are incredible. At the same time, it’s important to keep in mind that the majority of Hermit Thrush breed at lower elevations, in the hardwood forest. The range of the Hermit Thrush has only recently expanded to include New England. They first expanded into southern New England in the early 1990s (possibly associated with farm abandonment and reforestation), and quickly expanded northward. So while these steep declines for the spruce-fir zone are alarming, and parallel state-specific trends from the North American Breeding Bird survey (BBS), they don’t tell the full story. The BBS trends indicate that Hermit Thrush in Maine, for example, across all habitats are declining by <1% per year.
Data collected by the Breeding Bird Survey indicate that the size of the breeding population of Hermit Thrushes is steady or growing slowly. Population gains appear concentrated in eastern North America, exemplified by the ongoing colonization of the southern Appalachians. However, populations in western North America, the Mid-Atlantic and New England states, are likely declining.
Opportunities for Conservation
It’s not clear what’s driving declines of Hermit Thrush at high elevations in the Eastern U.S. or interior of the West. Hermit Thrush will benefit from general conservation measures such as maintaining intact, unfragmented forests; providing safe migration pathways; and taking measures to reduce atmospheric concentrations of greenhouse gases.
Hermit Thrush reach the upper limits of their elevational distribution in the lower zone of montane spruce-fir forests. Recent climate modeling by Audubon suggests that Hermit Thrush will disappear from New England over the next 100 years. Continued monitoring of this species as part of Mountain Birdwatch will help document the ecological impacts of ongoing climate change.