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Species · Colorado · BBS 2025 Release · 1966–2024

Swainson's Thrush Population Trend in Colorado

All statesForest birds

Swainson's Thrush in Colorado has surged: up 200% on the route-weighted index since 1974.

+200%Since 1974TrendPercent 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 →
49Routes In StateSurvey routesHow many standard-protocol BBS routes contributed counts. More routes means a steadier, better-sampled index; very thin coverage is suppressed.Full methodology →
51YearsYears surveyedNumber of years with at least one standard-protocol run in this geography. A longer record makes the trend more reliable.Full methodology →

Notable Swainson's Thrush Trends in ColoradoNotable 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 Colorado: up 200% on the route-weighted index since 1974.

Swainson's Thrush Population Forecast in Colorado

If the recent trend holds, Swainson's Thrush in Colorado is projected to stay roughly flat through 2029, near 0.40 (95% range 0.07–0.73). A 5-year backtest shows a typical error of ±26.4%, with 100% of held-out values landing inside the 95% band.

+9%Change by 2029TrendPercent 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 →
0.40Projected 2029 indexProjected indexThe central forecast of the abundance index if the recent trend continues. A projection of the current trajectory, not a prediction.Full methodology →
0.07–0.7395% 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 →
±26.4%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 in Colorado is projected to stay roughly flat through 2029, near 0.40 (95% range 0.07–0.73). A 5-year backtest shows a typical error of ±26.4%, with 100% of held-out values landing inside the 95% band.19702029
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 →
20250.390.060.72
20260.400.070.73
20270.400.070.73
20280.400.070.73
20290.400.070.73

Swainson's Thrush Survey Routes in Colorado

Routes recording Swainson's Thrush in Colorado.
Recent countThe raw number of individuals recorded on this route in its most recent survey year. A single-route tally, not a trend.Full methodology →
Aspen920241979
Yampa620231975
Parlin520221974
Stillwater Pass 2520242011
Dunckley Pas520241992
Rifle Falls520211998
Harmony419751975
Steamboat L.320242024
Comanche Pk320241996
Como320211994
Deadman Rd.320242013
Lost Lake220221990
Doyleville220211998
Buffalo Park220231992
Flattops220191992
Guanella Pas220241992
Pinon219951994
Nucla219991999
Lizard Head Pass220242001
Lake City 2220212018
Douglas Pass120162016
Buford120241987
Cheesman Lk120002000
Abarr119701970
Delta119741973

Swainson's Thrush Population Trend in Other States

alaskaarizonacaliforniaconnecticutidahoillinoismainemarylandmassachusettsmichiganminnesotamontananebraskanevadanew-hampshirenew-mexiconew-yorknorth-carolinaoregonpennsylvaniasouth-dakotautahvermontvirginiawashingtonwest-virginiawisconsinwyoming

Source: USGS North American Breeding Bird Survey, retrieved 2026-05-22.