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

Great Blue Heron Population Trend in Maryland

All statesWetland birds

Great Blue Heron in Maryland has surged: up 99% on the route-weighted index since 1968.

+99%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 →
58YearsYears 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 99% 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 108% by 2029 — from 1.3 in 2024 to a central estimate of 2.8 (95% range 1.4–4.2). A 5-year backtest shows a typical error of ±106.1%, with 0% of held-out values landing inside the 95% band.

+108%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 →
2.8Projected 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 →
1.4–4.295% 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 →
±106.1%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 108% by 2029 — from 1.3 in 2024 to a central estimate of 2.8 (95% range 1.4–4.2). A 5-year backtest shows a typical error of ±106.1%, with 0% of held-out values landing inside the 95% band.19662029
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 →
20252.61.34.0
20262.71.34.1
20272.71.34.1
20282.71.34.1
20292.81.44.2

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
Honga1520241967
Fair Hill619961992
Tall Timbers520141969
Madison520241967
Bald Friar519961992
Grove Neck419961992
Emmitsburg420241987
Upper Xrds420071989
Easton320191969
Jennings320232021
Forest Grove320232014
Ijamsville320241994
Davidsnville320231982
Williamsport220241999
Olney220241986
Norwood220101991
Jones219661966
Walnut220242005
Broomes Isl219941966
La Plata220091969
Pomonkey220241966
Northeast220161974
Millington220241967
Melitota220241967

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 2026-05-22.