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Species · Maryland · BBS 2025 Release · 1966–2024

Least Bittern Population Trend in Maryland

All statesWetland birds

Least Bittern in Maryland has surged: up 182% on the route-weighted index since 1969.

+182%Since 1969TrendPercent 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 →
4Routes 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 →
47YearsYears surveyedNumber of years with at least one standard-protocol run in this geography. A longer record makes the trend more reliable.Full methodology →

Notable Least Bittern 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 →

Least Bittern has surged in Maryland: up 182% on the route-weighted index since 1969.

Least Bittern Population Forecast in Maryland

If the recent trend holds, Least Bittern in Maryland is projected to rise about 21% by 2029 — from 0.07 in 2024 to a central estimate of 0.09 (95% range 0.00–0.17). A 5-year backtest shows a typical error of ±62%, with 100% of held-out values landing inside the 95% band.

+21%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 →
0.09Projected 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 →
0.00–0.1795% 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 →
±62%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, Least Bittern in Maryland is projected to rise about 21% by 2029 — from 0.07 in 2024 to a central estimate of 0.09 (95% range 0.00–0.17). A 5-year backtest shows a typical error of ±62%, with 100% 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 →
20250.080.000.17
20260.080.000.17
20270.090.000.17
20280.090.000.17
20290.090.000.17

Least Bittern Survey Routes in Maryland

Routes recording Least Bittern 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 →
Madison220241966
Golden Hill119691969
Honga120241968
Cokesbury120221976

Least Bittern Population Trend in Other States

alabamaarizonaarkansascaliforniaconnecticutdelawarefloridageorgiaillinoisindianaiowakansaslouisianamichiganminnesotamississippimissourinebraskanevadanew-hampshirenew-jerseynew-yorknorth-carolinanorth-dakotaohiooregonsouth-carolinasouth-dakotatexasvermontvirginiawisconsin

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