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

Brown-headed Cowbird Population Trend in Iowa

All statesGeneralists

Brown-headed Cowbird in Iowa has surged: up 85% on the route-weighted index since 1969.

+85%Since 1969TrendPercent 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 →
39Routes 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 IowaNotable 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 Iowa: up 85% on the route-weighted index since 1969.

Brown-headed Cowbird Population Forecast in Iowa

If the recent trend holds, Brown-headed Cowbird in Iowa is projected to stay roughly flat through 2029, near 27 (95% range 15–38). A 5-year backtest shows a typical error of ±6.1%, with 100% of held-out values landing inside the 95% band.

+6%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 →
27Projected 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 →
15–3895% 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 →
±6.1%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 Iowa is projected to stay roughly flat through 2029, near 27 (95% range 15–38). A 5-year backtest shows a typical error of ±6.1%, with 100% of held-out values landing inside the 95% band.19672029
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 →
2025261538
2026261538
2027271538
2028271538
2029271538

Brown-headed Cowbird Survey Routes in Iowa

Routes recording Brown-headed Cowbird in Iowa.
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 →
Scranton5720241967
Kanawha5520241967
Rock Valley4920241968
College Spgs4720041967
Pierson4720191968
Cedar Valley4619971967
Zearing4319951967
Burchinal4120241995
Mccallsburg4020241996
Bedford3820181968
Gaza3820231969
Neola3720161968
College Spgs 23720232005
Panther3320241967
Sioux City3320241968
Red Rock3020241968
Washington3020241967
Mt Hamill2720241967
Wales2720181967
Dinsdale2620241968
Titonka2420241968
Washta2320141967
Clare1820191967
Brooklyn1720221968
Alice1519991967

Brown-headed Cowbird Population Trend in Other States

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

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