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

Blue Grosbeak Population Trend in Iowa

All statesGeneralists

Blue Grosbeak in Iowa has surged: up 344% on the route-weighted index since 1970.

+344%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 →
17Routes 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 →
55YearsYears surveyedNumber of years with at least one standard-protocol run in this geography. A longer record makes the trend more reliable.Full methodology →

Notable Blue Grosbeak 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 →

Blue Grosbeak has surged in Iowa: up 344% on the route-weighted index since 1970.

Blue Grosbeak Population Forecast in Iowa

If the recent trend holds, Blue Grosbeak in Iowa is projected to rise about 65% by 2029 — from 0.50 in 2024 to a central estimate of 0.83 (95% range 0.26–1.4). A 5-year backtest shows a typical error of ±84.9%, with 80% of held-out values landing inside the 95% band.

+65%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 →
0.83Projected 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 →
0.26–1.495% 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 →
±84.9%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, Blue Grosbeak in Iowa is projected to rise about 65% by 2029 — from 0.50 in 2024 to a central estimate of 0.83 (95% range 0.26–1.4). A 5-year backtest shows a typical error of ±84.9%, with 80% 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 →
20250.790.221.3
20260.800.231.4
20270.810.241.4
20280.820.251.4
20290.830.261.4

Blue Grosbeak Survey Routes in Iowa

Routes recording Blue Grosbeak 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 →
Gaza720231970
College Spgs 2420222018
Mt Hamill320242008
Pierson320181968
Washta320141979
Sioux City320241973
Rock Valley220241968
Scranton220212021
Clare220192009
Exline120242015
Melrose120242024
College Spgs119711968
Bryant120232023
Williamsburg119941994
Mccallsburg120242019
Neola119811977
Wales120172013

Blue Grosbeak Population Trend in Other States

alabamaarizonaarkansascaliforniacoloradodelawarefloridageorgiaidahoillinoisindianakansaskentuckylouisianamarylandminnesotamississippimissourimontananebraskanevadanew-jerseynew-mexiconew-yorknorth-carolinanorth-dakotaohiooklahomapennsylvaniasouth-carolinasouth-dakotatennesseetexasutahvirginiawest-virginiawyoming

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