BirdAnalyst
Species · BBS 2025 Release · 1966–2024

Least Tern

LaridaeWetland birdsSternula antillarum

Least Tern has collapsed: down 90% on the route-weighted index since 1968.

-90%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 →
190RoutesSurvey routesHow many standard-protocol BBS routes contributed counts. More routes means a steadier, better-sampled index; very thin coverage is suppressed.Full methodology →
58Years SurveyedYears surveyedNumber of years with at least one standard-protocol run in this geography. A longer record makes the trend more reliable.Full methodology →

About the Least Tern

The Least Tern (Sternula antillarum) is a North American member of the Gulls, Terns & Skimmers (Laridae). In this analysis it is grouped with the wetland birds.

Size
8.5–31.5 in long (22–80 cm) — a long-winged waterbird (typical for the family)
Habitat
Marshes, ponds, lakeshores and other freshwater wetlands.
Diet
Aquatic invertebrates, small fish, frogs and plant matter.
Range
Recorded on 190 Breeding Bird Survey routes across 25 states, most concentrated in the Peninsular Florida.
Family
Laridae · Wetland birds

Notable Least Tern TrendsNotable 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 collapsed in surveyed states: down 90% on the route-weighted index since 1968.

Least Tern Population Forecast

If the recent trend holds, Least Tern is projected to stay roughly flat through 2029, near 0.01 (95% range 0.00–0.11). A 5-year backtest shows a typical error of ±79.9%, with 100% of held-out values landing inside the 95% band.

n/aChange 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 →
0.01Projected 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 →
0.00–0.1195% 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 →
±79.9%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, Least Tern is projected to stay roughly flat through 2029, near 0.01 (95% range 0.00–0.11). A 5-year backtest shows a typical error of ±79.9%, 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 →
20250.020.000.12
20260.020.000.12
20270.010.000.12
20280.010.000.11
20290.010.000.11

Where the Least Tern Is Detected

BBS routes recording Least Tern, sized by most recent count.

Least Tern Population Trend by State

Least Tern population trend by state.
TrendPercent 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 →Baseline yearThe first year of the smoothed window the trend is measured from. An earlier baseline means a longer record stands behind the number.Full methodology →Survey routesHow many standard-protocol BBS routes contributed counts. More routes means a steadier, better-sampled index; very thin coverage is suppressed.Full methodology →
Alabama-92%19686
Arkansas-27%19897
California+26%19745
Coloradoinsufficient datan/a2
Delaware-88%19687
Florida-98%196850
Georgiainsufficient datan/a5
Illinoisinsufficient datan/a3
Kansas-41%19695
Kentucky+126%19783
Louisiana+46%197115
Maineinsufficient datan/a1
Maryland-34%19809
Massachusetts-60%19717
Mississippi+45%19993
Missouriinsufficient datan/a3
Nebraska+103%20014
New Jersey-89%19806
New York-24%19743
North Carolina-39%19698
Oklahoma+85%19928
South Carolina-22%19993
Tennessee-28%19683
Texas+178%197122
Virginiainsufficient datan/a2

Least Tern Population Trend by Region

Bird Conservation Regions are the ecological unit for trends.

Least Tern population trend by Bird Conservation Region.
TrendPercent 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 →Baseline yearThe first year of the smoothed window the trend is measured from. An earlier baseline means a longer record stands behind the number.Full methodology →Survey routesHow many standard-protocol BBS routes contributed counts. More routes means a steadier, better-sampled index; very thin coverage is suppressed.Full methodology →
Central Mixed Grass Prairie-29%196912
Eastern Tallgrass Prairie+8%19977
Mississippi Alluvial Valley-67%196820
Southeastern Coastal Plain-97%196836
New England / Mid-Atlantic Coast-60%196832
Peninsular Florida-98%196839
Gulf Coastal Prairie+14%197124

Least Tern Conservation Status

Our route-weighted index shows it down about 90% since 1968.

Source: USGS North American Breeding Bird Survey, retrieved 2026-05-22. Trend is a route-weighted relative-abundance index, not an absolute population.