BirdAnalyst
Species · Colorado · BBS 2025 Release · 1966–2024

Brown Thrasher Population Trend in Colorado

All statesGeneralists

Brown Thrasher in Colorado has collapsed: down 81% on the route-weighted index since 1970.

-81%Since 1970TrendPercent 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 →
41Routes 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 →
53YearsYears surveyedNumber of years with at least one standard-protocol run in this geography. A longer record makes the trend more reliable.Full methodology →

Notable Brown Thrasher 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 declinecomputed 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 →

Brown Thrasher has collapsed in Colorado: down 81% on the route-weighted index since 1970.

Brown Thrasher Population Forecast in Colorado

If the recent trend holds, Brown Thrasher in Colorado is projected to rise about 19% by 2029 — from 0.11 in 2024 to a central estimate of 0.14 (95% range 0.00–0.43). A 5-year backtest shows a typical error of ±22.6%, with 100% of held-out values landing inside the 95% band.

+19%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 →
0.14Projected 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 →
0.00–0.4395% 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 →
±22.6%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, Brown Thrasher in Colorado is projected to rise about 19% by 2029 — from 0.11 in 2024 to a central estimate of 0.14 (95% range 0.00–0.43). A 5-year backtest shows a typical error of ±22.6%, with 100% of held-out values landing inside the 95% band.19682029
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 →
20250.140.000.44
20260.140.000.44
20270.140.000.44
20280.140.000.44
20290.140.000.43

Brown Thrasher Survey Routes in Colorado

Routes recording Brown Thrasher 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 →
Julesburg520212002
Timpas520102000
Two Buttes419971984
Fort Morgan420231996
Kirk420232005
Last Chance319991968
Boyero320161995
Wildhorse L320141990
Burlington320242003
Prospect Val320001995
Rockport220242013
Sheridan Lak220161995
Grover220241995
Doyle Bridge219951992
Neegrande220241993
Maybell119711970
Harmony120121986
Briggsdale120222003
Pinneo120091973
Fleming120231968
Kiowa120151968
Abarr120231970
Parlin120162007
Lamar120111977
Prospect Valley 2120232003

Brown Thrasher Population Trend in Other States

alabamaarkansasconnecticutdelawarefloridageorgiaillinoisindianaiowakansaskentuckylouisianamainemarylandmassachusettsmichiganminnesotamississippimissourimontananebraskanew-hampshirenew-jerseynew-mexiconew-yorknorth-carolinanorth-dakotaohiooklahomapennsylvaniarhode-islandsouth-carolinasouth-dakotatennesseetexasvermontvirginiawest-virginiawisconsinwyoming

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