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

Northern Bobwhite Population Trend in Illinois

All statesGrassland birds

Northern Bobwhite in Illinois has collapsed: down 80% on the route-weighted index since 1968.

-80%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 →
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 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 80% 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 95% by 2029 — from 6.6 in 2024 to a central estimate of 0.34 (95% range 0.00–11). A 5-year backtest shows a typical error of ±44.2%, with 100% of held-out values landing inside the 95% band.

-95%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 →
0.34Projected 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 →
0.00–1195% 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 →
±44.2%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, Northern Bobwhite in Illinois is projected to fall about 95% by 2029 — from 6.6 in 2024 to a central estimate of 0.34 (95% range 0.00–11). A 5-year backtest shows a typical error of ±44.2%, 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 →
20252.40.0013
20261.90.0013
20271.40.0012
20280.860.0012
20290.340.0011

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 →
Greenview3120241993
Athensville3020241971
Belleview3020241966
Kell2920242001
Chandlervill2420241971
Brownville2320241993
Marshall2320242001
Brnt Prairie2220241976
Mackinaw2120241966
Melrose2019991973
Concord2020241967
Concord West2020232001
Martinsville1920241970
Birds1920241976
Bradbury1820241970
Harristown1720242006
Sherrard1420231993
Mt Vernon1320241971
Beaucoup1220241971
Delwood1220241970
Robinson1220231970
Eldred1220211993
Bluff Spgs1120241967
York1120241993
Flora820241976

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 2026-05-22.