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

Purple Martin Population Trend in Illinois

All statesAerial insectivores

Purple Martin in Illinois has declined: down 44% on the route-weighted index since 1968.

-44%Since 1968TrendPercent 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 →
100Routes 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 →
58YearsYears surveyedNumber of years with at least one standard-protocol run in this geography. A longer record makes the trend more reliable.Full methodology →

Notable Purple Martin Trends in IllinoisNotable 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 Purple Martin in Illinois. See the full index history below.

Purple Martin Population Forecast in Illinois

If the recent trend holds, Purple Martin in Illinois is projected to fall about 66% by 2029 — from 5.9 in 2024 to a central estimate of 2.0 (95% range 0.00–5.0). A 5-year backtest shows a typical error of ±54.7%, with 60% of held-out values landing inside the 95% band.

-66%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 →
2.0Projected 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 →
0.00–5.095% 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 →
±54.7%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, Purple Martin in Illinois is projected to fall about 66% by 2029 — from 5.9 in 2024 to a central estimate of 2.0 (95% range 0.00–5.0). A 5-year backtest shows a typical error of ±54.7%, with 60% of held-out values landing inside the 95% band.19662029
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 →
20252.20.005.2
20262.20.005.1
20272.10.005.1
20282.10.005.0
20292.00.005.0

Purple Martin Survey Routes in Illinois

Routes recording Purple Martin in Illinois.
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 →
Seneca2620242009
Belknap2020241970
Bradbury1920241970
Humboldt1920241972
Mascoutah Lk1920241967
Bremen1920241969
Pawnee1820241967
Robinson1820231970
York1820241993
Athensville1720241971
Eubanks1720242001
Birds1520241976
Sherburnvill1420231967
Belleview1420241966
Janesville1420241976
Camp Point1420241994
Sheffield1220241966
Le Roy1220241993
Clayton1220242001
Chandlervill1120181971
Duncan Mills1120241997
Dudleyville1120242005
Martinsville1020241970
Terre Haute920241966
Sandusky820231993

Purple Martin Population Trend in Other States

alabamaarizonaarkansascaliforniacoloradoconnecticutdelawarefloridageorgiaindianaiowakansaskentuckylouisianamainemarylandmassachusettsmichiganminnesotamississippimissourimontananebraskanew-hampshirenew-jerseynew-mexiconew-yorknorth-carolinanorth-dakotaohiooklahomaoregonpennsylvaniarhode-islandsouth-carolinasouth-dakotatennesseetexasutahvermontvirginiawashingtonwest-virginiawisconsinwyoming

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