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

Northern Harrier Population Trend in Pennsylvania

All statesGeneralists

Northern Harrier in Pennsylvania has declined: down 29% on the route-weighted index since 1971.

-29%Since 1971TrendPercent 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 →
41Routes 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 →
40YearsYears 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 PennsylvaniaNotable signalsLong-arc shifts the engine flags automatically — sustained declines or increases large enough to stand out from year-to-year noise.Full methodology →

No notable trend signals for Northern Harrier in Pennsylvania. See the full index history below.

Northern Harrier Population Forecast in Pennsylvania

If the recent trend holds, Northern Harrier in Pennsylvania is projected to stay roughly flat through 2028, near 0.02 (95% range 0.00–0.05). A 5-year backtest shows a typical error of ±115.8%, with 100% of held-out values landing inside the 95% band.

n/aChange by 2028TrendPercent 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 →
0.02Projected 2028 indexProjected indexThe central forecast of the abundance index if the recent trend continues. A projection of the current trajectory, not a prediction.Full methodology →
0.00–0.0595% 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 →
±115.8%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, Northern Harrier in Pennsylvania is projected to stay roughly flat through 2028, near 0.02 (95% range 0.00–0.05). A 5-year backtest shows a typical error of ±115.8%, with 100% of held-out values landing inside the 95% band.19662028
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 →
20240.020.000.05
20250.020.000.05
20260.020.000.05
20270.020.000.05
20280.020.000.05

Northern Harrier Survey Routes in Pennsylvania

Routes recording Northern Harrier in Pennsylvania.
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 →
Shelocta220172017
Ryde219921992
Shrewsbury219961996
Slippery Rk119761970
Espyville119711971
Harmonsburg119951975
Ferris Crnrs119891989
Ellenton120041999
Teepleville119921966
Sigel119951995
N Washington119961996
Pottersdale119921992
Betula119871987
Sproul Sf-B120232022
Ridgway120052005
Rasselas120212021
Arnot120231983
Little Marsh120131988
Rosecrans120002000
Austinville120121991
Rush119901990
Bow Bridge120082002
Waller120142014
Millville120082007
Hop Bottom119701970

Northern Harrier Population Trend in Other States

alabamaalaskaarizonaarkansascaliforniacoloradodelawaregeorgiaidahoillinoisindianaiowakansaskentuckylouisianamainemarylandmassachusettsmichiganminnesotamissourimontananebraskanevadanew-hampshirenew-jerseynew-mexiconew-yorknorth-carolinanorth-dakotaohiooklahomaoregonrhode-islandsouth-dakotatennesseetexasutahvermontvirginiawashingtonwest-virginiawisconsinwyoming

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