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Species · Illinois · BBS 2025 Release · 1966–2024

Hooded Merganser Population Trend in Illinois

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Hooded Merganser in Illinois has collapsed: down 77% on the route-weighted index since 1994.

-77%Since 1994TrendPercent 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 →
18Routes 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 →
22YearsYears surveyedNumber of years with at least one standard-protocol run in this geography. A longer record makes the trend more reliable.Full methodology →

Notable Hooded Merganser 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 →

Hooded Merganser has collapsed in Illinois: down 77% on the route-weighted index since 1994.

Hooded Merganser Population Forecast in Illinois

If the recent trend holds, Hooded Merganser in Illinois is projected to stay roughly flat through 2029, near 0.04 (95% range 0.00–0.14). A 5-year backtest shows a typical error of ±353.8%, with 100% of held-out values landing inside the 95% band.

n/aChange 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 →
0.04Projected 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 →
0.00–0.1495% 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 →
±353.8%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, Hooded Merganser in Illinois is projected to stay roughly flat through 2029, near 0.04 (95% range 0.00–0.14). A 5-year backtest shows a typical error of ±353.8%, with 100% of held-out values landing inside the 95% band.19702029
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 →
20250.040.000.14
20260.040.000.14
20270.040.000.14
20280.040.000.14
20290.040.000.14

Hooded Merganser Survey Routes in Illinois

Routes recording Hooded Merganser 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 →
Cameron619891989
Beaverdam Lk519951970
Troy Grove420182018
Camp Point320112011
Concord West220102010
Newark220102010
Gulfport220142013
Seneca120242015
Payson120162016
Pawnee119981994
Kell120062006
Jamestown120122004
Beaucoup120122011
Grape Creek120222004
Olney120172017
Pulaski119961996
Dudleyville120102010
Minonk120042004

Hooded Merganser Population Trend in Other States

alabamaalaskaarkansascoloradoconnecticutidahoindianaiowakansaskentuckymainemarylandmassachusettsmichiganminnesotamississippimissourimontananebraskanew-hampshirenew-yorknorth-dakotaohiooklahomaoregonpennsylvaniarhode-islandsouth-carolinasouth-dakotatennesseetexasvermontwashingtonwest-virginiawisconsinwyoming

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