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

Black Tern Population Trend in Iowa

All statesWetland birds

Black Tern in Iowa has edged up: up 23% on the route-weighted index since 1971.

+23%Since 1971TrendPercent 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 →
15Routes 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 →
25YearsYears surveyedNumber of years with at least one standard-protocol run in this geography. A longer record makes the trend more reliable.Full methodology →

Notable Black Tern 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 →

No notable trend signals for Black Tern in Iowa. See the full index history below.

Black Tern Population Forecast in Iowa

If the recent trend holds, Black Tern in Iowa is projected to fall about 15% by 2030 — from 0.71 in 2025 to a central estimate of 0.60 (95% range 0.00–1.4). A 5-year backtest shows a typical error of ±221.6%, with 80% of held-out values landing inside the 95% band.

-15%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 →
0.60Projected 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 →
0.00–1.495% 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 →
±221.6%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, Black Tern in Iowa is projected to fall about 15% by 2030 — from 0.71 in 2025 to a central estimate of 0.60 (95% range 0.00–1.4). A 5-year backtest shows a typical error of ±221.6%, with 80% 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 →
20260.570.001.3
20270.570.001.3
20280.580.001.3
20290.590.001.3
20300.600.001.4

Black Tern Survey Routes in Iowa

Routes recording Black Tern 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 →
Washington2220251986
Scranton1319991973
Exline820072007
College Spgs619691969
Desmoines419681968
Panther420072007
Neola419781978
Rock Valley319721972
Sioux City320241969
Garner319771971
Titonka119801980
Gaza119691969
Melrose119891977
Lafayette120032003
Pierson120071969

Black Tern Population Trend in Other States

californiacoloradoidahoillinoisindianakansasmainemichiganminnesotamissourimontananebraskanevadanew-yorknorth-dakotaohiooregonsouth-dakotatexasutahwashingtonwisconsinwyoming

Source: USGS North American Breeding Bird Survey, retrieved 2026-08-14.