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The State of The Mountain Birds Report: 2020

The latest State of the Mountains Bird Report indicates steep and consistent declines for more than half of the 10 bird species monitored through Mountain Birdwatch.

Nearly a decade of monitoring by hundreds of citizen scientists has revealed that our mountain birds are facing challenging times in the northeastern United States. More than half of the 10 bird species (Yellow-bellied Flycatcher, Winter Wren, Bicknell’s Thrush, Swainson’s Thrush, Hermit Thrush, White-throated Sparrow, and Blackpoll Warbler) monitored by Mountain Birdwatch have experienced substantial declines since 2011.

Mean annual population trends (%) for the 10 avian species monitored through Mountain Birdwatch from 2011 through 2019. The color of the dot proceeding the mean annual trend estimate indicates the direction and confidence of the trend: (strong evidence for a negative trend), (likely negative trend), (likely positive trend), or (strong evidence for a positive trend). A trend of -2%, for example, indicates that the number of that species in our study area has declined by an average of 2% each year from 2011 through 2019. The 95% Bayesian credible interval is a measure of uncertainty surrounding the mean estimate.
SpeciesMean annual trend (%)95% credible interval
Yellow-bellied Flycatcher -2.45(-3.75, -1.10)
Black-capped Chickadee 3.14(0.25, 6.16)
Boreal Chickadee 1.24(-1.99, 4.38)
Winter Wren -3.41(-4.19, -2.62)
Bicknell's Thrush -2.41(-4.44, -0.45)
Swainson's Thrush -3.47(-4.35, -2.56)
Hermit Thrush -4.00(-6.14, -1.68)
Fox Sparrow 0.76(-3.27, 5.10)
White-throated Sparrow -5.50(-6.80, -4.09)
Blackpoll Warbler -5.1(-6.01, -4.15)

For example, our high-elevation populations of Blackpoll Warbler and White-throated Sparrow have both likely declined by >34% since 2011, and these populations have declining in all four states that are a part of the Mountain Birdwatch program: New York (Adirondacks and the Catskills), Vermont, New Hampshire, and Maine. White-throated Sparrows are short-distant migrants, commonly found at backyard New England bird feeders during the winter. Blackpoll Warblers, on the other hand, undertake long distance migrations to South America. These journeys require 2-3 days of non-stop flight down the Atlantic coast with stopovers in the Caribbean.

So what do these two species have in common then? Their populations are concentrated at high elevations (>1100 meters [>3609 feet]) within the mountains of the Northeast during the breeding season, and they are both highly susceptible to the effects of global climate change. As temperatures rise over the next 100 years, quantitative ecologists predict that both species will shift their breeding ranges northward. By 2120, it is likely that the breeding ranges of Blackpoll Warblers and White-throated Sparrows will be entirely restricted to the boreal forests of Canada and Alaska. Unfortunately, similar climate modeling also suggests the same pattern for most of the other declining species in the State of the Mountain Birds Report: Winter Wren, Yellow-bellied Flycatcher, and Swainson’s Thrush. On the other hand, Black-capped and Boreal Chickadee and Bicknell’s Thrush numbers are stable or slightly increasing in the northeastern U.S.

Given these forecasted changes, it is imperative that we continue to monitor these species through Mountain Birdwatch and document their responses to climate change, and other human-induced planetary changes like habitat loss and degradation. Here at VCE, and elsewhere, scientists are racing to find ways to slow and reverse these declining trends and northward shifts through such actions as habitat modification and (potentially) through reintroductions, translocation, and assisted migration. Without the baseline data of Mountain Birdwatch, we will not be in a strong position to fully understand how (or if) these management actions positively benefit these avian populations.

You can find the remainder of the 2020 report (e.g., more species-specific results, Methods, and Conservation Implications) via the web pages linked to the menu headings atop each page. If you find this report useful, please cite it (see sidebar for suggested citation) and the open access data and drop us a line (jhill at vtecostudies.org) to let us know how you used these data. Thank you.

State of Mountain Birds