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

Northern Harrier Population Trend in Colorado

All statesGeneralists

Northern Harrier in Colorado has collapsed: down 83% on the route-weighted index since 1970.

-83%Since 1970TrendPercent 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 →
85Routes 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 →
56YearsYears 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 ColoradoNotable 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 collapsed in Colorado: down 83% on the route-weighted index since 1970.

Northern Harrier Population Forecast in Colorado

If the recent trend holds, Northern Harrier in Colorado is projected to fall about 61% by 2029 — from 0.19 in 2024 to a central estimate of 0.07 (95% range 0.00–0.43). A 5-year backtest shows a typical error of ±33.2%, with 100% of held-out values landing inside the 95% band.

-61%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 →
0.00–0.4395% 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 →
±33.2%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 Colorado is projected to fall about 61% by 2029 — from 0.19 in 2024 to a central estimate of 0.07 (95% range 0.00–0.43). A 5-year backtest shows a typical error of ±33.2%, with 100% of held-out values landing inside the 95% band.19682029
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 →
20250.110.000.47
20260.100.000.46
20270.090.000.45
20280.080.000.44
20290.070.000.43

Northern Harrier Survey Routes in Colorado

Routes recording Northern Harrier in Colorado.
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 →
Adams Co.520211989
Great Divide320241976
Briggsdale320211968
Gilpin320111975
Waverly320191995
Cheyenne320181992
Last Chance 2320242017
Prospect Val320001992
Mosca320051992
Prospect Valley 2320222001
Pinneo220181980
Douglas Pass220232003
Abarr219991968
Moffat220151970
Two Buttes220091974
Wildhorse L220241989
Gordon Creek220221988
Pleasant View220212021
San Luis220091991
Browns Park220151994
Kirk220231993
Ninaview220042000
Timpas220061998
Mesita220082008
Maybell120241970

Northern Harrier Population Trend in Other States

alabamaalaskaarizonaarkansascaliforniadelawaregeorgiaidahoillinoisindianaiowakansaskentuckylouisianamainemarylandmassachusettsmichiganminnesotamissourimontananebraskanevadanew-hampshirenew-jerseynew-mexiconew-yorknorth-carolinanorth-dakotaohiooklahomaoregonpennsylvaniarhode-islandsouth-dakotatennesseetexasutahvermontvirginiawashingtonwest-virginiawisconsinwyoming

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