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

Northern Harrier Population Trend in Wisconsin

All statesGeneralists

Northern Harrier in Wisconsin has fallen sharply: down 52% on the route-weighted index since 1968.

-52%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 →
83Routes 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 Harrier Trends in WisconsinNotable 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 Harrier has fallen sharply in Wisconsin: down 52% on the route-weighted index since 1968.

Northern Harrier Population Forecast in Wisconsin

If the recent trend holds, Northern Harrier in Wisconsin is projected to stay roughly flat through 2029, near 0.25 (95% range 0.05–0.45). A 5-year backtest shows a typical error of ±199.2%, with 40% 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 →
0.25Projected 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 →
0.05–0.4595% 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 →
±199.2%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 Harrier in Wisconsin is projected to stay roughly flat through 2029, near 0.25 (95% range 0.05–0.45). A 5-year backtest shows a typical error of ±199.2%, with 40% 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 →
20250.260.060.45
20260.250.060.45
20270.250.060.45
20280.250.060.45
20290.250.050.45

Northern Harrier Survey Routes in Wisconsin

Routes recording Northern Harrier in Wisconsin.
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 →
Bayfield220191978
Dresser220221966
Loraine220181966
Phillips220221969
Merrill220231969
Rolling Pr220171966
Raymond219801980
Meridean220092009
Buena Vista220221998
Annaton220212003
Chaffey119951968
Iron River120161967
Minong120181969
Shanagolden119791972
Hudson120231967
Union Twp119861986
Cumberland120141966
Weyerhauser120221967
Couderay120011975
Exeland120221971
Gilman120171976
Holway119881968
Rib Lake120211975
Irma120221969
Mcnaughton119921992

Northern Harrier Population Trend in Other States

alabamaalaskaarizonaarkansascaliforniacoloradodelawaregeorgiaidahoillinoisindianaiowakansaskentuckylouisianamainemarylandmassachusettsmichiganminnesotamissourimontananebraskanevadanew-hampshirenew-jerseynew-mexiconew-yorknorth-carolinanorth-dakotaohiooklahomaoregonpennsylvaniarhode-islandsouth-dakotatennesseetexasutahvermontvirginiawashingtonwest-virginiawyoming

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