BirdAnalyst
Species · BBS 2026 Release · 1966–2025

Forster's Tern Population Analysis

LaridaeWetland birdsSterna forsteri

Forster's Tern has surged: up 114% on the route-weighted index since 1968.

+114%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 →
299RoutesSurvey routesHow many standard-protocol BBS routes contributed counts. More routes means a steadier, better-sampled index; very thin coverage is suppressed.Full methodology →
59Years 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 Forster's Tern

The Forster's Tern (Sterna forsteri) 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 299 Breeding Bird Survey routes across 31 states, most concentrated in the Great Basin.
Family
Laridae · Wetland birds

Notable Forster's 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 →

No notable trend signals for Forster's Tern. See the full index history below.

Forster's Tern Population Forecast

If the recent trend holds, Forster's Tern is projected to rise about 55% by 2030 — from 0.07 in 2025 to a central estimate of 0.12 (95% range 0.03–0.20). A 5-year backtest shows a typical error of ±77.4%, with 100% of held-out values landing inside the 95% band.

+55%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 →
0.12Projected 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 →
0.03–0.2095% 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 →
±77.4%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, Forster's Tern is projected to rise about 55% by 2030 — from 0.07 in 2025 to a central estimate of 0.12 (95% range 0.03–0.20). A 5-year backtest shows a typical error of ±77.4%, with 100% 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 →
20260.110.030.20
20270.110.030.20
20280.110.030.20
20290.110.030.20
20300.120.030.20

Where the Forster's Tern Is Detected

BBS routes recording Forster's Tern, sized by most recent count.

Forster's Tern Population Trend by State

Forster's 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-33%19714
California-67%197035
Colorado-77%19925
Delaware14×19779
Florida+44%197317
Georgiainsufficient datan/a2
Idaho-89%197714
Illinoisinsufficient datan/a1
Indianainsufficient datan/a1
Iowainsufficient datan/a2
Kansas-58%19693
Louisiana-87%197321
Maryland-62%196810
Michiganinsufficient datan/a1
Minnesota-8%197524
Montanainsufficient datan/a5
Nebraska-70%19886
Nevada-74%19886
New Jersey-55%19816
New Yorkinsufficient datan/a1
North Carolina-40%19736
North Dakota15×198118
Oregon-73%197120
South Carolinainsufficient datan/a1
South Dakota-21%196915
Texas+186%197025
Utah+1%19928
Virginia-66%19706
Washington-64%19918
Wisconsin-24%197412
Wyoming-64%19887

Forster's Tern Population Trend by Region

Bird Conservation Regions are the ecological unit for trends.

Forster's 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 →
Great Basin+36%197060
Northern Rockies-75%198116
Prairie Potholes+426%196946
Boreal Hardwood Transition-37%19828
Central Mixed Grass Prairie-90%19698
Prairie Hardwood Transition+69%197516
Southeastern Coastal Plain-77%196922
New England / Mid-Atlantic Coast+126%196831
Peninsular Florida+24%19739
Coastal California-72%197018
Gulf Coastal Prairie+170%197035

Forster's Tern Conservation Status

Our route-weighted index shows it up about 114% since 1968.

Source: USGS North American Breeding Bird Survey, retrieved 2026-08-14. Trend is a route-weighted relative-abundance index, not an absolute population.