BirdAnalyst
Species · BBS 2025 Release · 1966–2024

Royal Tern

LaridaeWetland birdsThalasseus maximus

Royal Tern has fallen sharply: down 70% on the route-weighted index since 1968.

-70%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 →
90RoutesSurvey 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 Royal Tern

The Royal Tern (Thalasseus maximus) 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 90 Breeding Bird Survey routes across 12 states, most concentrated in the Southeastern Coastal Plain.
Family
Laridae · Wetland birds

Notable Royal 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 →

Royal Tern has fallen sharply in surveyed states: down 70% on the route-weighted index since 1968.

Royal Tern Population Forecast

If the recent trend holds, Royal Tern is projected to stay roughly flat through 2029, near 0.04 (95% range 0.00–0.08). A 5-year backtest shows a typical error of ±51.8%, 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 →
0.04Projected 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 →
0.00–0.0895% 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 →
±51.8%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, Royal Tern is projected to stay roughly flat through 2029, near 0.04 (95% range 0.00–0.08). A 5-year backtest shows a typical error of ±51.8%, 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 →
20250.040.000.09
20260.040.000.09
20270.040.000.09
20280.040.000.08
20290.040.000.08

Where the Royal Tern Is Detected

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

Royal Tern Population Trend by State

Royal 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+262%19717
Californiainsufficient datan/a3
Delawareinsufficient datan/a1
Florida-80%196828
Georgiainsufficient datan/a2
Louisiana-65%19826
Marylandinsufficient datan/a8
New Jerseyinsufficient datan/a1
North Carolina-81%196811
South Carolinainsufficient datan/a2
Texas+249%197613
Virginia-76%19788

Royal Tern Population Trend by Region

Bird Conservation Regions are the ecological unit for trends.

Royal 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-66%196833
New England / Mid-Atlantic Coast-54%196917
Peninsular Florida-89%196818
Gulf Coastal Prairie+141%197617

Royal Tern Conservation Status

Our route-weighted index shows it down about 70% 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.