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

Blue Jay Population Trend in Illinois

All statesForest birds

Blue Jay in Illinois has fallen sharply: down 52% on the route-weighted index since 1968.

-52%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 →
105Routes 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 →
59YearsYears 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 Jay 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 →

long arc declinecomputed 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 Jay has fallen sharply in Illinois: down 52% on the route-weighted index since 1968.

Blue Jay Population Forecast in Illinois

If the recent trend holds, Blue Jay in Illinois is projected to fall about 34% by 2030 — from 6.1 in 2025 to a central estimate of 4.1 (95% range 1.8–6.3). A 5-year backtest shows a typical error of ±20.2%, with 100% of held-out values landing inside the 95% band.

-34%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 →
4.1Projected 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 →
1.8–6.395% 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 →
±20.2%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 Jay in Illinois is projected to fall about 34% by 2030 — from 6.1 in 2025 to a central estimate of 4.1 (95% range 1.8–6.3). A 5-year backtest shows a typical error of ±20.2%, with 100% of held-out values landing inside the 95% band.19662030
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 →
20264.62.36.8
20274.42.26.7
20284.32.16.6
20294.22.06.4
20304.11.86.3

Blue Jay Survey Routes in Illinois

Routes recording Blue Jay 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 →
Wayne2320251966
Caledonia2220251993
Eldred2220251993
Melrose2119991973
Sheffield1720241966
Eubanks1720252001
Kell1720252001
Lake Galena1620212001
Chandlervill1520251971
Mt Vernon1420251971
Royalton1420252001
Belknap1320251970
Alden1320252019
Holcomb1220251971
Concord1220251967
Mascoutah Lk1220251967
Delwood1220251970
Guilford1020231967
Humphrey1020251972
St Morgan1020221967
Birds1020241976
Athens1020251995
Humboldt920251970
Sandusky920231993
Union920172001

Blue Jay Population Trend in Other States

alabamaarkansascoloradoconnecticutdelawarefloridageorgiaindianaiowakansaskentuckylouisianamainemarylandmassachusettsmichiganminnesotamississippimissourimontananebraskanew-hampshirenew-jerseynew-mexiconew-yorknorth-carolinanorth-dakotaohiooklahomapennsylvaniarhode-islandsouth-carolinasouth-dakotatennesseetexasvermontvirginiawest-virginiawisconsinwyoming

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