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

Northern Harrier Population Trend in Delaware

All statesGeneralists

Northern Harrier in Delaware has increased: up 26% on the route-weighted index since 1979.

+26%Since 1979TrendPercent 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 →
6Routes 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 Northern Harrier Trends in DelawareNotable 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 Delaware. See the full index history below.

Northern Harrier Population Forecast in Delaware

If the recent trend holds, Northern Harrier in Delaware is projected to fall about 20% by 2029 — from 0.20 in 2024 to a central estimate of 0.16 (95% range 0.00–0.35). A 5-year backtest shows a typical error of ±16.7%, with 100% of held-out values landing inside the 95% band.

-20%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 →
0.16Projected 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 →
0.00–0.3595% 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 →
±16.7%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 Delaware is projected to fall about 20% by 2029 — from 0.20 in 2024 to a central estimate of 0.16 (95% range 0.00–0.35). A 5-year backtest shows a typical error of ±16.7%, with 100% of held-out values landing inside the 95% band.19722029
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 →
20250.160.000.35
20260.160.000.35
20270.160.000.35
20280.160.000.35
20290.160.000.35

Northern Harrier Survey Routes in Delaware

Routes recording Northern Harrier in Delaware.
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 →
Dover219791979
Mt Pleasant119961996
Wilmington119961996
Harrington120241972
Blackbird120111995
Georgetown119921992

Northern Harrier Population Trend in Other States

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

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