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

Blue Jay Population Trend in Illinois

All statesGeneralists

Blue Jay in Illinois has fallen sharply: down 54% on the route-weighted index since 1968.

-54%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 →
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 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 54% 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 25% by 2029 — from 5.5 in 2024 to a central estimate of 4.1 (95% range 1.9–6.3). A 5-year backtest shows a typical error of ±16.5%, with 100% of held-out values landing inside the 95% band.

-25%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 →
4.1Projected 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 →
1.9–6.395% 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 →
±16.5%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 25% by 2029 — from 5.5 in 2024 to a central estimate of 4.1 (95% range 1.9–6.3). A 5-year backtest shows a typical error of ±16.5%, with 100% 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 →
20254.62.46.8
20264.52.26.7
20274.32.16.6
20284.22.06.4
20294.11.96.3

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 →
Wayne2620241966
Melrose2119991973
Terre Haute2020241966
Caledonia2020241993
Sheffield1720241966
Lake Galena1620212001
Eldred1420211993
Alden1320232019
Brnt Prairie1220241976
Mt Vernon1220241971
Duncan Mills1220241993
Guilford1020231967
Mill Creek1020241966
Geneseo1020211967
Athensville1020241971
St Morgan1020221967
Birds1020241976
Sherrard1020241993
Royalton1020242001
Concord920241967
Mascoutah Lk920241967
Belknap920241970
Camp Point920241993
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 2026-05-22.