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Species · South Dakota · BBS 2026 Release · 1966–2025

Swainson's Thrush Population Trend in South Dakota

All statesForest birds

Swainson's Thrush in South Dakota has surged: up 22× on the route-weighted index since 1972.

22×Since 1972TrendPercent 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 →
13Routes 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 South DakotaNotable 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 South Dakota: up 22× on the route-weighted index since 1972.

Swainson's Thrush Population Forecast in South Dakota

If the recent trend holds, Swainson's Thrush in South Dakota is projected to rise about 19% by 2030 — from 1.5 in 2025 to a central estimate of 1.8 (95% range 0.11–3.5). A 5-year backtest shows a typical error of ±78.7%, with 100% of held-out values landing inside the 95% band.

+19%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 →
1.8Projected 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 →
0.11–3.595% 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 →
±78.7%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 in South Dakota is projected to rise about 19% by 2030 — from 1.5 in 2025 to a central estimate of 1.8 (95% range 0.11–3.5). A 5-year backtest shows a typical error of ±78.7%, with 100% of held-out values landing inside the 95% band.19692030
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 →
20261.70.013.4
20271.70.043.5
20281.80.063.5
20291.80.093.5
20301.80.113.5

Swainson's Thrush Survey Routes in South Dakota

Routes recording Swainson's Thrush in South Dakota.
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 →
Black Fox3120171992
Long Draw3020251992
Norbeck2920021992
Englewood1720211992
Rochford1020251996
Silver City620121993
Custer320251970
Lightning Cr220002000
Hazelrodt120221995
Hill City120131996
Elk Mountain120041998
Wind Cave Np120132013
Roubaix Lk119901969

Swainson's Thrush Population Trend in Other States

alaskaarizonacaliforniacoloradoconnecticutidahoillinoismainemarylandmassachusettsmichiganminnesotamontananebraskanevadanew-hampshirenew-mexiconew-yorknorth-carolinaoregonpennsylvaniautahvermontvirginiawashingtonwest-virginiawisconsinwyoming

Source: USGS North American Breeding Bird Survey, retrieved 2026-08-14.