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

Tree Swallow Population Trend in Iowa

All statesAerial insectivores

Tree Swallow in Iowa has surged: up 25× on the route-weighted index since 1970.

25×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 →
37Routes 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 →
54YearsYears surveyedNumber of years with at least one standard-protocol run in this geography. A longer record makes the trend more reliable.Full methodology →

Notable Tree Swallow 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 →

Tree Swallow has surged in Iowa: up 25× on the route-weighted index since 1970.

Tree Swallow Population Forecast in Iowa

If the recent trend holds, Tree Swallow in Iowa is projected to fall about 69% by 2030 — from 11 in 2025 to a central estimate of 3.3 (95% range 0.65–5.9). A 5-year backtest shows a typical error of ±74.3%, with 60% of held-out values landing inside the 95% band.

-69%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 →
3.3Projected 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 →
0.65–5.995% 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 →
±74.3%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, Tree Swallow in Iowa is projected to fall about 69% by 2030 — from 11 in 2025 to a central estimate of 3.3 (95% range 0.65–5.9). A 5-year backtest shows a typical error of ±74.3%, with 60% 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 →
20263.00.405.7
20273.10.475.7
20283.20.535.8
20293.20.595.9
20303.30.655.9

Tree Swallow Survey Routes in Iowa

Routes recording Tree Swallow 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 →
Bryant25820251983
Lafayette2520252003
Festina1720251975
Prairieburg1220251968
West Liberty1120071986
Melrose1020241980
Hudson920221985
Burchinal720241995
Cedar Valley619961996
Washta620251978
Exline520221980
Scranton320131978
Clare320071992
Pierson320191970
Davis Corner320251980
Titonka320251983
Bedford220172000
Williamsburg220221972
Desmoines219711969
Panther220151997
Maquoketa220191986
Alice219971986
Dinsdale219711971
Sioux City220251981
Rock Valley220191982

Tree Swallow 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.