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

Brown-headed Cowbird Population Trend in Iowa

All statesGeneralists

Brown-headed Cowbird in Iowa has surged: up 78% on the route-weighted index since 1969.

+78%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 →
58YearsYears 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 78% 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 2030, near 27 (95% range 16–38). A 5-year backtest shows a typical error of ±5.9%, with 100% of held-out values landing inside the 95% band.

-3%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 →
27Projected 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 →
16–3895% 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 →
±5.9%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 2030, near 27 (95% range 16–38). A 5-year backtest shows a typical error of ±5.9%, with 100% of held-out values landing inside the 95% band.19672030
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 →
2026271538
2027271538
2028271638
2029271638
2030271638

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 →
Kanawha7520251967
Titonka6220251968
Mccallsburg5620251996
Hudson5520251967
Rock Valley5420251968
College Spgs4720041967
Cedar Valley4619971967
Zearing4319951967
Burchinal3920251995
Red Rock3720251968
Davis Corner3420251968
Sioux City3220251968
Washta3120251967
Wales3020251967
Washington2920251967
Scranton2720251967
Brooklyn2620251968
Neola2520251968
Gaza2520251969
Panther2420251967
Mt Hamill2220251967
Pierson2220251968
Melrose2120251974
Dinsdale2120251968
Bryant1920251967

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 2026-08-14.