A project of

Swainson's Thrush

The State of Swainson’s Thrushes

Regionally: Declining

A plot of Swainson's Thrush study area abundance. The x axis show years between 2010 and 2021. The y axis shows local population size. Local population size fluctuates between roughly 1700 and 1000 individuals with an overall downward trend from 2010 to 2021.

The mean (thick, dark red line) annual estimate of the Swainson’s 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).

Swainson’s Thrush numbers have likely decreased since Mountain Birdwatch began. Annual fluctuations are evident, but overall counts of this species have steadily declined in the northeast U.S. over the last half-century. Mountain Birdwatch data indicate an average decline of -1.38% per year (95% credible interval = -2.06% to -0.69%) in the mountains of our region; this trend equates to a -14.08% decline in population (95% credible interval = -20.45% to -7.29%) between 2010 and 2021 (see table below).

Mean annual population trends and population change (with 95% Bayesian credible intervals [CRI]) for Swainson's Thrush from 2010 through 2021. A red dot indicates strong evidence for a negative trend. An orange dot indicates weak evidence for a negative trend.
RegionMean annual
trend (%)
Trend
95% CRI
Probability of
decrease
Probability of
increase
Population
change (%)
2010-2021
Population
change (95% CRI)
All regions -1.38(-2.06, -0.69)>0.99<0.01-14.08(-20.45, -7.29)
New York
(state)
-1.02(-2.26, 0.30)0.940.06-10.43(-22.19, 3.40)
New York
(Catskills)
-0.37(-2.94, 2.58)0.620.38-2.91(-28.00, 32.39)
New York
(Adirondacks)
-1.15(-2.48, 0.24)0.940.06-11.68(-24.13. 2.63)
Vermont -0.51(-1.71, 0.75)0.790.21-5.23(-17.28, 8.52)
New Hampshire -2.58(-3.45, -1.71)>0.99<0.01-24.88(-32.02, -17.26)
Maine -0.50(-1.43, 0.47)0.840.16-5.28(-14.62, 5.32)

Globally: Declining 

Data collected by the Breeding Bird Survey indicate widespread declines in Swainson’s Thrush numbers throughout North America (~0.5% per year). These declines appear to have begun in the early 1980s, and are most severe across the northern and western portion of the Swainson’s Thrush range. They have disappeared from many locales, such as coastal areas and major interior valleys, that they once inhabited in California. Counts of this species made at several migratory stopover sites (e.g., Long Point Bird Observatory) have declined as well. Areas where population trends are increasing for Swainson’s Thrush include the southern Appalachian Mountains, Eastern Montana and the Western Dakotas, and Alaska.

 

State of the Mountain Birds