BirdAnalyst
Species · BBS 2025 Release · 1966–2024

Gull-billed Tern

LaridaeWetland birdsGelochelidon nilotica

Gull-billed Tern has surged: up 101% on the route-weighted index since 1968.

+101%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 →
56RoutesSurvey 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 Gull-billed Tern

The Gull-billed Tern (Gelochelidon nilotica) 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 56 Breeding Bird Survey routes across 12 states, most concentrated in the Gulf Coastal Prairie.
Family
Laridae · Wetland birds

Notable Gull-billed 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 Gull-billed Tern. See the full index history below.

Gull-billed Tern Population Forecast

If the recent trend holds, Gull-billed Tern is projected to stay roughly flat through 2029, near 0.02 (95% range 0.00–0.04). A 5-year backtest shows a typical error of ±221.4%, with 80% 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 →
0.02Projected 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 →
0.00–0.0495% 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 →
±221.4%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, Gull-billed Tern is projected to stay roughly flat through 2029, near 0.02 (95% range 0.00–0.04). A 5-year backtest shows a typical error of ±221.4%, 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 →
20250.020.000.04
20260.020.000.04
20270.020.000.04
20280.020.000.04
20290.020.000.04

Where the Gull-billed Tern Is Detected

BBS routes recording Gull-billed Tern, sized by most recent count.

Gull-billed Tern Population Trend by State

Gull-billed 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-94%19854
Californiainsufficient datan/a1
Delawareinsufficient datan/a1
Florida-21%197213
Georgiainsufficient datan/a1
Louisiana-18%19975
Marylandinsufficient datan/a2
Mississippiinsufficient datan/a1
North Carolina-90%19685
South Carolinainsufficient datan/a2
Texas+63%197120
Virginiainsufficient datan/a1

Gull-billed Tern Population Trend by Region

Bird Conservation Regions are the ecological unit for trends.

Gull-billed 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 →
Southeastern Coastal Plain-75%196818
Tamaulipan Brushlands+13%19854
Gulf Coastal Prairie+75%197120

Gull-billed Tern Conservation Status

Our route-weighted index shows it up about 101% 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.