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Species · Illinois · BBS 2026 Release · 1966–2025

Northern Bobwhite Population Trend in Illinois

All statesGame birds

Northern Bobwhite in Illinois has collapsed: down 79% on the route-weighted index since 1968.

-79%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 →
97Routes 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 Northern Bobwhite 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 →

Northern Bobwhite has collapsed in Illinois: down 79% on the route-weighted index since 1968.

Northern Bobwhite Population Forecast in Illinois

If the recent trend holds, Northern Bobwhite in Illinois is projected to fall about 98% by 2030 — from 6.9 in 2025 to a central estimate of 0.15 (95% range 0.00–11). A 5-year backtest shows a typical error of ±56.8%, with 100% of held-out values landing inside the 95% band.

-98%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 →
0.15Projected 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 →
0.00–1195% 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 →
±56.8%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, Northern Bobwhite in Illinois is projected to fall about 98% by 2030 — from 6.9 in 2025 to a central estimate of 0.15 (95% range 0.00–11). A 5-year backtest shows a typical error of ±56.8%, 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 →
20262.20.0013
20271.70.0012
20281.20.0012
20290.670.0011
20300.150.0011

Northern Bobwhite Survey Routes in Illinois

Routes recording Northern Bobwhite 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 →
Greenview3920251993
Chandlervill3020251971
Brownville2820251993
Athensville2720251971
Marshall2320252001
Bluff Spgs2220251967
Kell2220252001
Mackinaw2120251966
Martinsville2120251970
Melrose2019991973
Belleview2020251966
Birds1920241976
Concord West1820252001
Gulfport1520251971
Brnt Prairie1520251976
Bradbury1420251970
Mt Vernon1420251971
Concord1320251967
Royalton1320252001
Robinson1220231970
Pawnee1120251967
Bremen1120251969
Stillwell920251971
Janesville920251972
Mascoutah Lk920251967

Northern Bobwhite Population Trend in Other States

alabamaarkansascoloradoconnecticutdelawarefloridageorgiaidahoindianaiowakansaskentuckylouisianamainemarylandmassachusettsmichiganminnesotamississippimissourinebraskanew-hampshirenew-jerseynew-mexiconew-yorknorth-carolinaohiooklahomaoregonpennsylvaniarhode-islandsouth-carolinasouth-dakotatennesseetexasvermontvirginiawashingtonwest-virginiawisconsinwyoming

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