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Species · Montana · BBS 2025 Release · 1966–2024

Brown-headed Cowbird Population Trend in Montana

All statesGeneralists

Brown-headed Cowbird in Montana has surged: up 251% on the route-weighted index since 1970.

+251%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 →
116Routes 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 Brown-headed Cowbird 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 →

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 →

Brown-headed Cowbird has surged in Montana: up 250% on the route-weighted index since 1970.

Brown-headed Cowbird Population Forecast in Montana

If the recent trend holds, Brown-headed Cowbird in Montana is projected to rise about 16% by 2029 — from 18 in 2024 to a central estimate of 21 (95% range 15–26). A 5-year backtest shows a typical error of ±25.4%, with 80% of held-out values landing inside the 95% band.

+16%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 →
21Projected 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 →
15–2695% 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 →
±25.4%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-headed Cowbird in Montana is projected to rise about 16% by 2029 — from 18 in 2024 to a central estimate of 21 (95% range 15–26). A 5-year backtest shows a typical error of ±25.4%, with 80% 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 →
2025201425
2026201426
2027201526
2028201526
2029211526

Brown-headed Cowbird Survey Routes in Montana

Routes recording Brown-headed Cowbird 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 →
Redstone7520241968
Glentana7520242015
Powderville6620241968
Chinook6620242015
Albion6520241982
Oswego6320241978
Winifred5520232023
Lindsay5520242015
Roy5420241988
Cabin Creek5320242018
Flatwillow4720081968
Ingomar4720241977
Westby4720242015
Webster4220241978
Augusta3620241976
Ester Lake3420242015
Glasgow3320241968
Reed Point3320241977
Custer3320222019
Lambert3220242021
Virgelle3120241979
Circle3020231970
Whitlash2820242009
Harlem2720211971
Shawmut2620241979

Brown-headed Cowbird Population Trend in Other States

alabamaalaskaarizonaarkansascaliforniacoloradoconnecticutdelawarefloridageorgiaidahoillinoisindianaiowakansaskentuckylouisianamainemarylandmassachusettsmichiganminnesotamississippimissourinebraskanevadanew-hampshirenew-jerseynew-mexiconew-yorknorth-carolinanorth-dakotaohiooklahomaoregonpennsylvaniarhode-islandsouth-carolinasouth-dakotatennesseetexasutahvermontvirginiawashingtonwest-virginiawisconsinwyoming

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