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Species · Iowa · BBS 2025 Release · 1966–2024

Bell's Vireo Population Trend in Iowa

All statesForest birds

Bell's Vireo in Iowa has surged: up 186% on the route-weighted index since 1969.

+186%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 →
23Routes 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 →
51YearsYears surveyedNumber of years with at least one standard-protocol run in this geography. A longer record makes the trend more reliable.Full methodology →

Notable Bell's Vireo 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 →

Bell's Vireo has surged in Iowa: up 186% on the route-weighted index since 1969.

Bell's Vireo Population Forecast in Iowa

If the recent trend holds, Bell's Vireo in Iowa is projected to rise about 109% by 2029 — from 0.27 in 2024 to a central estimate of 0.57 (95% range 0.29–0.85). A 5-year backtest shows a typical error of ±40.9%, with 80% of held-out values landing inside the 95% band.

+109%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 →
0.57Projected 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 →
0.29–0.8595% 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 →
±40.9%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, Bell's Vireo in Iowa is projected to rise about 109% by 2029 — from 0.27 in 2024 to a central estimate of 0.57 (95% range 0.29–0.85). A 5-year backtest shows a typical error of ±40.9%, with 80% 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 →
20250.530.250.81
20260.540.260.82
20270.550.270.83
20280.560.280.84
20290.570.290.85

Bell's Vireo Survey Routes in Iowa

Routes recording Bell's Vireo 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 →
College Spgs 2320232008
Exline220241974
Melrose220231992
Bedford220181989
Brooklyn220222014
Williamsburg220232023
Red Rock220241999
Wales220161989
Mt Hamill120161974
College Spgs120031967
Bryant119871987
West Liberty120211989
Cedar Valley119851971
Panther120242024
Washington120211976
Neola120151968
Maquoketa119941969
Alice119991987
Hudson119901990
Washta120131991
Sioux City120241984
Rock Valley119731973
Lafayette120152015

Bell's Vireo Population Trend in Other States

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