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

Northern Harrier Population Trend in Maryland

All statesGeneralists

Northern Harrier in Maryland has declined: down 26% on the route-weighted index since 1972.

-26%Since 1972TrendPercent 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 →
17Routes 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 →
34YearsYears 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 MarylandNotable 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 Maryland. See the full index history below.

Northern Harrier Population Forecast in Maryland

If the recent trend holds, Northern Harrier in Maryland is projected to stay roughly flat through 2028, near 0.03 (95% range 0.00–0.08). A 5-year backtest shows a typical error of ±31.9%, 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 →
0.03Projected 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 →
0.00–0.0895% 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 →
±31.9%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 Maryland is projected to stay roughly flat through 2028, near 0.03 (95% range 0.00–0.08). A 5-year backtest shows a typical error of ±31.9%, with 100% of held-out values landing inside the 95% band.19692028
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 →
20240.030.000.08
20250.030.000.08
20260.030.000.08
20270.030.000.08
20280.030.000.08

Northern Harrier Survey Routes in Maryland

Routes recording Northern Harrier in Maryland.
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 →
Emmitsburg220231985
Elkton119931991
Millington119961983
Melitota120162016
Piney Neck119821982
Williamsport120082008
Matthews120032003
Easton119961996
Golden Hill119911969
Honga120001973
Norwood120022002
Madison120171969
Cokesbury120092009
Newark119961985
Grove Neck119961996
Madonna120182018
Broomes Isl119891989

Northern Harrier Population Trend in Other States

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

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