Study: Mountain Birds Facing Steep Decline

by NEW YORK DIGITAL NEWS


Bicknell’s thrush sitting on its nest, courtesy of Kent McFarland (provided by DEC)Fourteen years of monitoring by many hundreds of community scientists has revealed that mountain birds face challenging times and significant declines in the Northeast.

Research sheds light on the underlying driving forces behind these declines, with climate change likely a root cause.

Mountain Birdwatch, a citizen science project of the Vermont Center for Ecostudies, monitors ten bird species in the spruce-fir zone. These species are a mix of montane specialists (e.g., Blackpoll Warbler), intermediaries that occur in the lower hardwoods and spruce-fir (e.g., Swainson’s Thrush), and lower elevation species that are likely to colonize higher elevation areas as the climate warms (e.g., Black-capped Chickadee).

Their annual monitoring of nearly 800 montane locations has revealed that most of the species that we monitor (Yellow-bellied Flycatcher, Winter Wren, Bicknell’s Thrush, Swainson’s Thrush, Hermit Thrush, Blackpoll Warbler, and White-throated Sparrow) have declined by an average of 40% since 2010.

graph showing the estimated percent population change between 2010 and 2023 for all 10 focal bird species monitored via Mountain BirdwatchThe most persistent declines continue to occur in the Catskills (at the southern periphery of the northeastern spruce-fir zone), where 7 of the 8 monitored bird species declined by an average of 57% since 2010.  (Fox Sparrow and Boreal Chickadee do not breed in the Catskills, and only Black-capped Chickadees increased there.)

The 2023 State of the Mountains Bird Report report is alarming advocates say, because it indicates declines of greater than 60% since 2010 for both Hermit Thrush and White-throated Sparrow — two species that are declining essentially everywhere they breed in the United States.

Many species’ distribution models have predicted that species whose core populations occur at mid-elevations (e.g., Swainson’s and Hermit Thrush) may temporarily benefit from climate change by following warming patterns to higher elevations as their preferred climate envelope shifts upslope into newly-suitable(-to-them) habitat.

That most of the mid-elevation and spruce-fir bird species show declining trends, suggests that there may be actually be fewer species than hypothesized that are poised to benefit from climate disruption at higher elevations.

All bird species and population segments that nest within the high elevation spruce-fir zone are highly susceptible to the effects of global climate change.

As temperatures continue to rise, quantitative ecologists predict that boreal species will shift their breeding ranges upslope and poleward.

By the end of this century, it is likely that the breeding ranges of dozens of our spruce-fir forest breeders (e.g., both crossbill species, Canada Jay, and Bay-breasted and Blackpoll Warblers) will be entirely restricted to the boreal forests of Canada and Alaska. You can see these climate and species’ distribution models at Audubon’s Survival by Degrees website.

You can find the 2023 State of the Mountains Bird Report here.

Illustrations, from above: Bicknell’s thrush sitting on its nest, courtesy of Kent McFarland (provided by DEC); and a graph showing the estimated percent population change between 2010 and 2023 for all 10 focal bird species monitored via Mountain Birdwatch. Positive values indicate a population increase, while negative values indicate a decline compared to 2010. For example, an increase of 100% indicates a doubling of the population size since 2010. The credible intervals (a measure of each species’ uncertainty) are omitted for clarity. (Here is a larger version).

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