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Species · Massachusetts · BBS 2025 Release · 1966–2024

Least Tern Population Trend in Massachusetts

All statesWetland birds

Least Tern in Massachusetts has fallen sharply: down 60% on the route-weighted index since 1971.

-60%Since 1971TrendPercent 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 →
7Routes 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 →
19YearsYears 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 Tern Trends in MassachusettsNotable 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 declinecomputed 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 Tern has fallen sharply in Massachusetts: down 60% on the route-weighted index since 1971.

Least Tern Population Forecast in Massachusetts

If the recent trend holds, Least Tern in Massachusetts is projected to fall about 100% by 2029 — from 1.4 in 2024 to a central estimate of 0.00 (95% range 0.00–2.3). A 5-year backtest shows a typical error of ±303.1%, with 80% of held-out values landing inside the 95% band.

-100%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 →
0.00Projected 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 →
0.00–2.395% 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 →
±303.1%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, Least Tern in Massachusetts is projected to fall about 100% by 2029 — from 1.4 in 2024 to a central estimate of 0.00 (95% range 0.00–2.3). A 5-year backtest shows a typical error of ±303.1%, with 80% 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 →
20250.060.002.3
20260.040.002.3
20270.010.002.3
20280.000.002.3
20290.000.002.3

Least Tern Survey Routes in Massachusetts

Routes recording Least Tern in Massachusetts.
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 →
Gay Head2120242013
Wellfleet 2820232023
Chilmark419831969
Newburyport319971983
E Dennis220001969
Wellfleet119931966
Cape Cod Ns119961989

Least Tern Population Trend in Other States

alabamaarkansascaliforniacoloradodelawarefloridageorgiaillinoiskansaskentuckylouisianamainemarylandmississippimissourinebraskanew-jerseynew-yorknorth-carolinaoklahomasouth-carolinatennesseetexasvirginia

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