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

Brewer's Sparrow Population Trend in Colorado

All statesGeneralists

Brewer's Sparrow in Colorado has surged: up 103% on the route-weighted index since 1970.

+103%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 →
117Routes 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 →
56YearsYears surveyedNumber of years with at least one standard-protocol run in this geography. A longer record makes the trend more reliable.Full methodology →

Notable Brewer's Sparrow 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 →

Brewer's Sparrow has surged in Colorado: up 103% on the route-weighted index since 1970.

Brewer's Sparrow Population Forecast in Colorado

If the recent trend holds, Brewer's Sparrow in Colorado is projected to fall about 25% by 2029 — from 8.7 in 2024 to a central estimate of 6.6 (95% range 2.1–11). A 5-year backtest shows a typical error of ±18.7%, with 100% of held-out values landing inside the 95% band.

-25%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 →
6.6Projected 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 →
2.1–1195% 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 →
±18.7%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, Brewer's Sparrow in Colorado is projected to fall about 25% by 2029 — from 8.7 in 2024 to a central estimate of 6.6 (95% range 2.1–11). A 5-year backtest shows a typical error of ±18.7%, 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 →
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Brewer's Sparrow Survey Routes in Colorado

Routes recording Brewer's Sparrow 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 →
Browns Park9820241992
Great Divide8420241974
Walden8020241990
Lay7420241996
Maybell6920241972
Dinosaur6920241995
Black Sulphur Cr4320242015
Wray Gulch3820231988
Angora3520241998
Yampa3420231969
Yellowjacket Pass3220241998
Piedra3019991999
Wilson Creek2820241990
Baxter Pass2820242013
Powderhorn2720231994
Antonito2720041995
Piceance Basin2220121998
Mosca2120241992
Basin1920241995
Blanca1719871979
Mesita1620242005
Rockport1520241994
Doyleville1420241988
Douglas Pass1320241982
Nunn1220211995

Brewer's Sparrow Population Trend in Other States

arizonacaliforniaidahokansasmontananebraskanevadanew-mexiconorth-dakotaoklahomaoregonsouth-dakotatexasutahwashingtonwyoming

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