A project of

Hermit Thrush

The State of Hermit Thrushes

Regionally: Declining

A plot of Hermit Thrush study area abundance. The x axis show years between 2010 and 2021. The y axis shows local population size. Local population size increased slightly to approximately 240 in 2014, then dropped steeply in the next year to approximately 130 individuals and has been steadily decreasing to less than 100 individuals in 2021.

The mean (thick, dark red line) annual estimate of the Hermit Thrush abundance within the immediate areas surrounding ~750 Mountain Birdwatch sampling stations. The lighter vertical bars represent the 95% Bayesian credible interval (a measure of the uncertainty around the abundance estimates).

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 above, paint an interesting picture. Numbers of Hermit Thrush were clearly on the rise from 2010 to 2014, but then the population suddenly declined (by nearly 50%) where it has slowly declined since 2015. 

RegionMean annual
trend (%)
Trend
95% CRI
Probability of
decrease
Probability of
increase
Population
change (%)
2010-2021
Population
change (95% CRI)
All regions -6.92(-8.97, -4.76)>0.99<0.01-54.22(-64.42, -41.53)
New York
(state)
-11.26(-14.41, -7.80)>0.99<0.01-72.59(-81.94, -59.09)
New York
(Catskills)
-15.86(-20.94, -9.03)>0.99<0.01-83.80(-92.45, -64.71)
New York
(Adirondacks)
-9.87(-13.12, -6.35)>0.99<0.01-67.44(-78.72, -51.43)
Vermont -7.85(-10.99, -4.40)>0.99<0.01-58.55(-72.22, -39.02)
New Hampshire -0.39(-3.52, 2.94)0.560.44-2.68(-32.56, 37.50)
Maine -9.53(-13.38, -5.81)>0.99<0.01-65.91(-79.41, -48.21)

Those trends for the spruce-fir zone in the Adirondacks (-11.26% per year) and the Catskills (-15.86% 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 the northeastern U.S. 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 much of 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. 

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.

Globally: Stable

Data collected by the Breeding Bird Survey indicate that the size of the breeding population of Hermit Thrushes has remained stable. 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.

State of the Mountain Birds