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

Brewer's Sparrow Population Trend in Montana

All statesGeneralists

Brewer's Sparrow in Montana has declined: down 35% on the route-weighted index since 1970.

-35%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 →
84Routes 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 MontanaNotable signalsLong-arc shifts the engine flags automatically — sustained declines or increases large enough to stand out from year-to-year noise.Full methodology →

No notable trend signals for Brewer's Sparrow in Montana. See the full index history below.

Brewer's Sparrow Population Forecast in Montana

If the recent trend holds, Brewer's Sparrow in Montana is projected to fall about 17% by 2029 — from 4.0 in 2024 to a central estimate of 3.3 (95% range 0.00–6.9). A 5-year backtest shows a typical error of ±9.7%, with 100% of held-out values landing inside the 95% band.

-17%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 →
3.3Projected 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 →
0.00–6.995% 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 →
±9.7%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 Montana is projected to fall about 17% by 2029 — from 4.0 in 2024 to a central estimate of 3.3 (95% range 0.00–6.9). A 5-year backtest shows a typical error of ±9.7%, 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 →
20253.40.007.1
20263.40.007.1
20273.30.007.0
20283.30.007.0
20293.30.006.9

Brewer's Sparrow Survey Routes in Montana

Routes recording Brewer's Sparrow in Montana.
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 →
Beaverhead8420241973
Boulder3820241969
Custer3720222019
Brunzell Slough3420242015
Red Rock2420241973
Custer 22420242024
Lima1920241995
Winnett1420232017
Brandenberg1320191968
Flatwillow 21320232011
Roundup1320242016
Cleveland1220241980
Hebgen Lake1120242017
Two Dot1020091976
Ingomar1020231968
Willow Creek 21020241982
Freeman Creek1020162015
Harlem820211968
Brusett720241983
Chestnut720241968
Forsyth620231992
Albion620231982
Shelby620222017
Hehn Draw620242016
Malta520241975

Brewer's Sparrow Population Trend in Other States

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