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

Black Tern Population Trend in Iowa

All statesWetland birds

Black Tern in Iowa has surged: up 172% on the route-weighted index since 1971.

+172%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 →
24YearsYears 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 →

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 →

Black Tern has surged in Iowa: up 172% on the route-weighted index since 1971.

Black Tern Population Forecast in Iowa

If the recent trend holds, Black Tern in Iowa is projected to rise about 313% by 2029 — from 0.14 in 2024 to a central estimate of 0.56 (95% range 0.00–1.3). A 5-year backtest shows a typical error of ±187.9%, with 80% of held-out values landing inside the 95% band.

+313%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 →
0.56Projected 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 →
0.00–1.395% 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 →
±187.9%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, Black Tern in Iowa is projected to rise about 313% by 2029 — from 0.14 in 2024 to a central estimate of 0.56 (95% range 0.00–1.3). A 5-year backtest shows a typical error of ±187.9%, 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 →
20250.530.001.3
20260.540.001.3
20270.550.001.3
20280.560.001.3
20290.560.001.3

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 →
Scranton1319991973
Exline820072007
College Spgs619691969
Desmoines419681968
Panther420072007
Neola419781978
Rock Valley319721972
Sioux City320241969
Garner319771971
Titonka119801980
Gaza119691969
Melrose119891977
Washington120171986
Lafayette120032003
Pierson120071969

Black Tern Population Trend in Other States

californiacoloradoidahoillinoisindianakansasmainemichiganminnesotamissourimontananebraskanevadanew-yorknorth-dakotaohiooregonsouth-dakotatexasutahwashingtonwisconsinwyoming

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