BirdAnalyst
Species · BBS 2026 Release · 1966–2025

Swainson's Thrush Population Analysis

TurdidaeForest birdsCatharus ustulatus

Swainson's Thrush has surged: up 629% on the route-weighted index since 1968.

+629%Since 1968TrendPercent change in the route-weighted abundance index between a smoothed baseline window and the most recent one. It tracks direction, not absolute population.Full methodology →
857RoutesSurvey routesHow many standard-protocol BBS routes contributed counts. More routes means a steadier, better-sampled index; very thin coverage is suppressed.Full methodology →
59Years SurveyedYears surveyedNumber of years with at least one standard-protocol run in this geography. A longer record makes the trend more reliable.Full methodology →

About the Swainson's Thrush

The Swainson's Thrush (Catharus ustulatus) is a North American member of the Thrushes (Turdidae). In this analysis it is grouped with the forest birds.

Size
6–11 in long (15–28 cm) — a medium songbird (typical for the family)
Habitat
Woodlands and forest edges, including wooded suburbs and parks.
Diet
Insects and spiders gleaned from foliage and bark, with seeds and berries in season.
Range
Recorded on 857 Breeding Bird Survey routes across 29 states, most concentrated in the Northern Pacific Rainforest.
Family
Turdidae · Forest birds

Notable Swainson's Thrush TrendsNotable signalsLong-arc shifts the engine flags automatically — sustained declines or increases large enough to stand out from year-to-year noise.Full methodology →

long arc increasecomputed indexTrend sourceWhether the figure is our own computed route-weighted index or an official USGS modeled estimate. The current build labels every trend as computed.Full methodology →

Swainson's Thrush has surged in surveyed states: up 629% on the route-weighted index since 1968.

Swainson's Thrush Population Forecast

If the recent trend holds, Swainson's Thrush is projected to rise about 24% by 2030 — from 2.8 in 2025 to a central estimate of 3.5 (95% range 2.9–4.2). A 5-year backtest shows a typical error of ±13.7%, with 100% of held-out values landing inside the 95% band.

+24%Change by 2030TrendPercent change in the route-weighted abundance index between a smoothed baseline window and the most recent one. It tracks direction, not absolute population.Full methodology →
3.5Projected 2030 indexProjected indexThe central forecast of the abundance index if the recent trend continues. A projection of the current trajectory, not a prediction.Full methodology →
2.9–4.295% range95% rangeThe 95% uncertainty band around the projection at the forecast horizon. The true value should land inside it most of the time.Full methodology →
±13.7%Backtest errorBacktest errorTypical error when we hold out the most recent years, forecast them, and compare to what actually happened. Lower means a more trustworthy projection.Full methodology →
If the recent trend holds, Swainson's Thrush is projected to rise about 24% by 2030 — from 2.8 in 2025 to a central estimate of 3.5 (95% range 2.9–4.2). A 5-year backtest shows a typical error of ±13.7%, with 100% of held-out values landing inside the 95% band.19662030
Projection of the recent trend (dashed) with 80/95% bands — a projection, not a prediction. Habitat, climate, and land use are not modeled.
YearProjected indexProjected indexThe central forecast of the abundance index if the recent trend continues. A projection of the current trajectory, not a prediction.Full methodology →95% low95% rangeThe 95% uncertainty band around the projection at the forecast horizon. The true value should land inside it most of the time.Full methodology →95% high95% rangeThe 95% uncertainty band around the projection at the forecast horizon. The true value should land inside it most of the time.Full methodology →
20263.32.74.0
20273.42.74.0
20283.42.84.1
20293.52.84.1
20303.52.94.2

Where the Swainson's Thrush Is Detected

BBS routes recording Swainson's Thrush, sized by most recent count.

Swainson's Thrush Population Trend by State

Swainson's Thrush population trend by state.
TrendPercent change in the route-weighted abundance index between a smoothed baseline window and the most recent one. It tracks direction, not absolute population.Full methodology →Baseline yearThe first year of the smoothed window the trend is measured from. An earlier baseline means a longer record stands behind the number.Full methodology →Survey routesHow many standard-protocol BBS routes contributed counts. More routes means a steadier, better-sampled index; very thin coverage is suppressed.Full methodology →
Alaska-8%1972109
Arizonainsufficient datan/a1
California-4%1970103
Colorado+255%197450
Connecticutinsufficient datan/a3
Idaho+155%197139
Illinoisinsufficient datan/a1
Maine-51%196863
Marylandinsufficient datan/a1
Massachusetts-49%19704
Michigan+26%197334
Minnesota+176%196929
Montana+142%197046
Nebraskainsufficient datan/a1
Nevadainsufficient datan/a5
New Hampshire-6%196814
New Mexicoinsufficient datan/a3
New York-62%196836
North Carolinainsufficient datan/a1
Oregon-21%197089
Pennsylvania-76%196917
South Dakota22×197213
Utah-90%197529
Vermont+37%196816
Virginiainsufficient datan/a1
Washington-32%197082
West Virginia+83%19896
Wisconsin-54%197121
Wyoming-1%197040

Swainson's Thrush Population Trend by Region

Bird Conservation Regions are the ecological unit for trends.

Swainson's Thrush population trend by Bird Conservation Region.
TrendPercent change in the route-weighted abundance index between a smoothed baseline window and the most recent one. It tracks direction, not absolute population.Full methodology →Baseline yearThe first year of the smoothed window the trend is measured from. An earlier baseline means a longer record stands behind the number.Full methodology →Survey routesHow many standard-protocol BBS routes contributed counts. More routes means a steadier, better-sampled index; very thin coverage is suppressed.Full methodology →
BCR 2-56%19947
BCR 4+8%197667
Northern Pacific Rainforest-8%1970155
Great Basin-34%197067
Northern Rockies+45%1970133
Boreal Hardwood Transition+183%196977
Lower Great Lakes / St. Lawrence Plain-38%19716
Atlantic Northern Forest-20%1968119
Sierra Nevada+63%197416
Southern Rockies / Colorado Plateau+148%197280
Badlands and Prairies12×197225
Appalachian Mountains+117%196933
Coastal California+27%197047

Swainson's Thrush Conservation Status

Our route-weighted index shows it up about 629% since 1968.

Source: USGS North American Breeding Bird Survey, retrieved 2026-08-14. Trend is a route-weighted relative-abundance index, not an absolute population.