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

Brown-headed Cowbird Population Trend in Colorado

All statesGeneralists

Brown-headed Cowbird in Colorado has surged: up 391% on the route-weighted index since 1970.

+391%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 →
158Routes 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 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 →

Brown-headed Cowbird has surged in Colorado: up 391% on the route-weighted index since 1970.

Brown-headed Cowbird Population Forecast in Colorado

If the recent trend holds, Brown-headed Cowbird in Colorado is projected to rise about 58% by 2029 — from 3.9 in 2024 to a central estimate of 6.2 (95% range 2.8–9.6). A 5-year backtest shows a typical error of ±71.2%, with 100% of held-out values landing inside the 95% band.

+58%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 →
6.2Projected 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 →
2.8–9.695% 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 →
±71.2%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 Colorado is projected to rise about 58% by 2029 — from 3.9 in 2024 to a central estimate of 6.2 (95% range 2.8–9.6). A 5-year backtest shows a typical error of ±71.2%, 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 →
20256.02.69.4
20266.12.79.5
20276.12.79.5
20286.12.79.6
20296.22.89.6

Brown-headed Cowbird Survey Routes in Colorado

Routes recording Brown-headed Cowbird 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 →
Falfa2920241971
Dolores2619871969
Julesburg2420211998
Ragged Mtn.2020191994
Wildhorse L1920241989
Amherst1820241992
Douglas Pass1720241985
Pleasant View1720212021
Boyero1620171986
Pinos Creek1519901988
Pagosa Spgs1419821975
Fort Morgan1320241996
Yampa1220231971
Guffey1220241990
Kirk1220231992
Yellowjacket Pass1220241998
Pinneo1120191974
Alamosa1120241988
Aspen1020241979
Fruita1020071988
Tarryall1020231988
Walsenburg1020241994
Grover920241992
Lay920241996
Briggsdale820241989

Brown-headed Cowbird Population Trend in Other States

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

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