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

Henslow's Sparrow Population Trend in Illinois

All statesGrassland birds

Henslow's Sparrow in Illinois has risen sharply: up 51% on the route-weighted index since 1973.

+51%Since 1973TrendPercent 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 →
33Routes 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 →
39YearsYears surveyedNumber of years with at least one standard-protocol run in this geography. A longer record makes the trend more reliable.Full methodology →

Notable Henslow's Sparrow 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 increasecomputed 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 →

Henslow's Sparrow has risen sharply in Illinois: up 51% on the route-weighted index since 1973.

Henslow's Sparrow Population Forecast in Illinois

If the recent trend holds, Henslow's Sparrow in Illinois is projected to rise about 10% by 2029 — from 0.07 in 2024 to a central estimate of 0.07 (95% range 0.01–0.14). A 5-year backtest shows a typical error of ±15.9%, with 100% of held-out values landing inside the 95% band.

+10%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 →
0.07Projected 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 →
0.01–0.1495% 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 →
±15.9%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, Henslow's Sparrow in Illinois is projected to rise about 10% by 2029 — from 0.07 in 2024 to a central estimate of 0.07 (95% range 0.01–0.14). A 5-year backtest shows a typical error of ±15.9%, with 100% of held-out values landing inside the 95% band.19692029
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 →
20250.070.010.13
20260.070.010.13
20270.070.010.14
20280.070.010.14
20290.070.010.14

Henslow's Sparrow Survey Routes in Illinois

Routes recording Henslow's Sparrow 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 →
Alden420192019
Buda320162003
Milford320132013
Wayne220222010
Fairbury220232022
Bluff Spgs220222022
Sterling220082008
Grape Creek220052005
Delwood220241988
Guilford120171969
Mill Creek120072007
Geneseo119731973
Sheffield120242024
Compton119731973
Streator120242013
Newark120152015
New Lenox119801971
Terre Haute120062006
Mackinaw120171983
Pontiac120022002
Belleview119891989
Rosamond120072007
Lake Galena120122002
Clayton120242024
Gridley120232018

Henslow's Sparrow Population Trend in Other States

delawareindianaiowakansaskentuckymarylandmichiganminnesotamissourinebraskanew-yorknorth-carolinanorth-dakotaohiooklahomapennsylvaniasouth-dakotavermontvirginiawest-virginiawisconsin

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