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

Brown-headed Cowbird Population Trend in Colorado

All statesGeneralists

Brown-headed Cowbird in Colorado has surged: up 415% on the route-weighted index since 1970.

+415%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 →
159Routes 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 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 415% 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 41% by 2030 — from 4.3 in 2025 to a central estimate of 6.1 (95% range 2.7–9.5). A 5-year backtest shows a typical error of ±69.7%, with 100% of held-out values landing inside the 95% band.

+41%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 →
6.1Projected 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 →
2.7–9.595% 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 →
±69.7%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, Brown-headed Cowbird in Colorado is projected to rise about 41% by 2030 — from 4.3 in 2025 to a central estimate of 6.1 (95% range 2.7–9.5). A 5-year backtest shows a typical error of ±69.7%, 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 →
20266.02.59.4
20276.02.69.4
20286.02.69.5
20296.12.69.5
20306.12.79.5

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 →
Fort Morgan6220251996
Dolores2619871969
Yellowjacket Pass2620251998
Julesburg2420211998
Ragged Mtn.2020191994
Tarryall1920251988
Amherst1820241992
Douglas Pass1720241985
Pleasant View1720212021
Boyero1620171986
Gilpin1520251971
Pinos Creek1519901988
Pagosa Spgs1419821975
Walsenburg1420251994
Fleming1320251990
Wildhorse L1320251989
Arsenal 21320252016
Yampa1220231971
Falfa1220251971
Kirk1220231992
Deadman Rd.1120251992
Fruita1020071988
Paonia1020251992
Neegrande1020251993
Pinneo920251974

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 2026-08-14.