BirdAnalyst
Species · BBS 2025 Release · 1966–2024

Common Tern

LaridaeWetland birdsSterna hirundo

Common Tern has collapsed: down 97% on the route-weighted index since 1968.

-97%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 →
119RoutesSurvey 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 Common Tern

The Common Tern (Sterna hirundo) 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 119 Breeding Bird Survey routes across 27 states, most concentrated in the New England / Mid-Atlantic Coast.
Family
Laridae · Wetland birds

Notable Common 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 →

Common Tern has collapsed in surveyed states: down 97% on the route-weighted index since 1968.

Common Tern Population Forecast

If the recent trend holds, Common Tern is projected to stay roughly flat through 2029, near 0.00 (95% range 0.00–0.12). A 5-year backtest shows a typical error of ±1414.8%, 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 →
0.00Projected 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 →
0.00–0.1295% 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 →
±1414.8%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, Common Tern is projected to stay roughly flat through 2029, near 0.00 (95% range 0.00–0.12). A 5-year backtest shows a typical error of ±1414.8%, 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 →
20250.000.000.12
20260.000.000.12
20270.000.000.12
20280.000.000.12
20290.000.000.12

Where the Common Tern Is Detected

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

Common Tern Population Trend by State

Common 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 →
Alabamainsufficient datan/a2
Alaskainsufficient datan/a1
Connecticutinsufficient datan/a1
Delaware-90%19685
Floridainsufficient datan/a2
Idahoinsufficient datan/a1
Indianainsufficient datan/a3
Louisiana-63%19795
Maine-62%19686
Maryland-54%19687
Massachusetts-75%19696
Michiganinsufficient datan/a4
Minnesotainsufficient datan/a8
Montana-83%197610
New Jersey-87%19815
New York-97%19689
North Carolina-75%19695
North Dakota+174%197917
Ohioinsufficient datan/a2
Rhode Islandinsufficient datan/a1
South Dakotainsufficient datan/a2
Texasinsufficient datan/a6
Vermontinsufficient datan/a1
Virginiainsufficient datan/a4
Washingtoninsufficient datan/a1
Wisconsin-86%19693
Wyominginsufficient datan/a2

Common Tern Population Trend by Region

Bird Conservation Regions are the ecological unit for trends.

Common 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 →
Prairie Potholes+86%198025
Boreal Hardwood Transition-89%19698
Lower Great Lakes / St. Lawrence Plain-64%19756
Atlantic Northern Forest+304%19845
Prairie Hardwood Transition-90%19708
Southeastern Coastal Plain+5%19699
New England / Mid-Atlantic Coast-96%196835
Gulf Coastal Prairie+24%197611

Common Tern Conservation Status

Our route-weighted index shows it down about 97% 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.