BirdAnalyst
Species · Colorado · BBS 2026 Release · 1966–2025

Brewer's Sparrow Population Trend in Colorado

All statesArid-land birds

Brewer's Sparrow in Colorado has surged: up 93% on the route-weighted index since 1970.

+93%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 →
118Routes 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 →
57YearsYears 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 93% 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 stay roughly flat through 2030, near 6.5 (95% range 2.1–11). A 5-year backtest shows a typical error of ±18.5%, with 100% of held-out values landing inside the 95% band.

+3%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 →
6.5Projected 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 →
2.1–1195% 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 →
±18.5%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 stay roughly flat through 2030, near 6.5 (95% range 2.1–11). A 5-year backtest shows a typical error of ±18.5%, with 100% of held-out values landing inside the 95% band.19682030
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 →
Great Divide8220251974
Maybell7620251972
Lay6120251996
Dinosaur6020251995
Walden5920251990
Wray Gulch5320251988
Browns Park4720251992
Black Sulphur Cr4020252015
Yampa3420231969
Mosca3320251992
Piedra3019991999
Baxter Pass2820242013
Antonito2720041995
Piceance Basin2220121998
Blanca1719871979
Doyleville1720251988
Mesita1620242005
Rockport1520241994
Wilson Creek1420251990
Nunn1420251995
Douglas Pass1320241982
Powderhorn1320251994
Paonia1120251992
Colona1020141972
Edison1020181988

Brewer's Sparrow Population Trend in Other States

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