BirdAnalyst
Species · Maryland · BBS 2026 Release · 1966–2025

Great Blue Heron Population Trend in Maryland

All statesWetland birds

Great Blue Heron in Maryland has surged: up 101% on the route-weighted index since 1968.

+101%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 →
73Routes 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 →
59YearsYears surveyedNumber of years with at least one standard-protocol run in this geography. A longer record makes the trend more reliable.Full methodology →

Notable Great Blue Heron 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 →

long arc increasecomputed 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 →

Great Blue Heron has surged in Maryland: up 101% on the route-weighted index since 1968.

Great Blue Heron Population Forecast in Maryland

If the recent trend holds, Great Blue Heron in Maryland is projected to rise about 122% by 2030 — from 1.2 in 2025 to a central estimate of 2.7 (95% range 1.3–4.1). A 5-year backtest shows a typical error of ±115.2%, with 20% of held-out values landing inside the 95% band.

+122%Change by 2030TrendPercent 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 →
2.7Projected 2030 indexProjected indexThe central forecast of the abundance index if the recent trend continues. A projection of the current trajectory, not a prediction.Full methodology →
1.3–4.195% 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 →
±115.2%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, Great Blue Heron in Maryland is projected to rise about 122% by 2030 — from 1.2 in 2025 to a central estimate of 2.7 (95% range 1.3–4.1). A 5-year backtest shows a typical error of ±115.2%, with 20% of held-out values landing inside the 95% band.19662030
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 →
20262.61.24.0
20272.61.24.0
20282.61.24.1
20292.71.24.1
20302.71.34.1

Great Blue Heron Survey Routes in Maryland

Routes recording Great Blue Heron 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 →
St. George'S Island11420172015
Honga920251967
Fair Hill619961992
Tall Timbers520141969
Bald Friar519961992
Grove Neck419961992
Upper Xrds420071989
Millington420251967
Melitota420251967
Madison420251967
Williamsport320251999
Easton320191969
Cokesbury320251967
Jennings320232021
Forest Grove320232014
Berlin320251985
Emmitsburg220251987
Olney220241986
Norwood220101991
Jones219661966
Walnut220242005
Broomes Isl219941966
La Plata220091969
Pomonkey220241966
Northeast220161974

Great Blue Heron Population Trend in Other States

alabamaalaskaarizonaarkansascaliforniacoloradoconnecticutdelawarefloridageorgiaidahoillinoisindianaiowakansaskentuckylouisianamainemassachusettsmichiganminnesotamississippimissourimontananebraskanevadanew-hampshirenew-jerseynew-mexiconew-yorknorth-carolinanorth-dakotaohiooklahomaoregonpennsylvaniarhode-islandsouth-carolinasouth-dakotatennesseetexasutahvermontvirginiawashingtonwest-virginiawisconsinwyoming

Source: USGS North American Breeding Bird Survey, retrieved 2026-08-14.