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

Brown-headed Cowbird Population Trend in Illinois

All statesGeneralists

Brown-headed Cowbird in Illinois has surged: up 155% on the route-weighted index since 1968.

+155%Since 1968
105Routes In State
58Years

Notable Brown-headed Cowbird Trends in Illinois

long arc increasecomputed index

Brown-headed Cowbird has surged in Illinois: up 155% on the route-weighted index since 1968.

Brown-headed Cowbird Population Forecast in Illinois

If the recent trend holds, Brown-headed Cowbird in Illinois is projected to stay roughly flat through 2029, near 23 (95% range 19–28). A 5-year backtest shows a typical error of ±11.7%, with 80% of held-out values landing inside the 95% band.

+1%Change by 2029
23Projected 2029 index
19–2895% range
±11.7%Backtest error
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 index95% low95% high
2025221827
2026231827
2027231827
2028231828
2029231928

Brown-headed Cowbird Survey Routes in Illinois

Routes recording Brown-headed Cowbird in Illinois.
Belleview8220241966
Chandlervill6520241971
Fairland5620241967
Monticello4820241976
Stillwell4520241971
Grape Creek4420242001
Mill Creek4320241966
Terre Haute4320241966
Buda4220231977
Cave In Rock4120241993
Atkinson4020241966
Sherrard4020241993
Milford3920231966
Duncan Mills3920241993
Streator3820241972
Camp Point3820241993
Harristown3720242001
Guilford3520231967
Pulaski3520241970
York3520241993
New Lenox3420191966
Fairbury3320241976
Janesville3320241972
Delwood3320241970
Gridley3320242001

Brown-headed Cowbird Population Trend in Other States

alabamaalaskaarizonaarkansascaliforniacoloradoconnecticutdelawarefloridageorgiaidahoindianaiowakansaskentuckylouisianamainemarylandmassachusettsmichiganminnesotamississippimissourimontananebraskanevadanew-hampshirenew-jerseynew-mexiconew-yorknorth-carolinanorth-dakotaohiooklahomaoregonpennsylvaniarhode-islandsouth-carolinasouth-dakotatennesseetexasutahvermontvirginiawashingtonwest-virginiawisconsinwyoming

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