BirdAnalyst
Species · BBS 2026 Release · 1966–2025

Caspian Tern Population Analysis

LaridaeWetland birdsHydroprogne caspia

Caspian Tern has risen sharply: up 61% on the route-weighted index since 1968.

+61%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 →
248RoutesSurvey 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 Caspian Tern

The Caspian Tern (Hydroprogne caspia) 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 248 Breeding Bird Survey routes across 26 states, most concentrated in the Great Basin.
Family
Laridae · Wetland birds

Notable Caspian 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 Caspian Tern. See the full index history below.

Caspian Tern Population Forecast

If the recent trend holds, Caspian Tern is projected to stay roughly flat through 2030, near 0.07 (95% range 0.01–0.12). A 5-year backtest shows a typical error of ±332.2%, with 0% of held-out values landing inside the 95% band.

n/aChange 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 →
0.07Projected 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 →
0.01–0.1295% 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 →
±332.2%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, Caspian Tern is projected to stay roughly flat through 2030, near 0.07 (95% range 0.01–0.12). A 5-year backtest shows a typical error of ±332.2%, with 0% 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 →
20260.070.010.12
20270.070.010.12
20280.070.010.12
20290.070.010.12
20300.070.010.12

Where the Caspian Tern Is Detected

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

Caspian Tern Population Trend by State

Caspian 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-25%19704
Alaskainsufficient datan/a1
California-24%197054
Delawareinsufficient datan/a3
Florida-21%197622
Idaho-81%19869
Illinoisinsufficient datan/a2
Indianainsufficient datan/a1
Louisiana-17%19718
Marylandinsufficient datan/a4
Michigan-33%198314
Minnesota-9%198514
Montanainsufficient datan/a8
Nevada-37%19974
North Carolinainsufficient datan/a1
North Dakotainsufficient datan/a4
Oregon-14%197525
South Carolinainsufficient datan/a2
South Dakotainsufficient datan/a1
Texas+18%197415
Utah+75%199511
Vermontinsufficient datan/a1
Virginiainsufficient datan/a1
Washington-53%197928
Wisconsininsufficient datan/a2
Wyominginsufficient datan/a9

Caspian Tern Population Trend by Region

Bird Conservation Regions are the ecological unit for trends.

Caspian 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 →
Northern Pacific Rainforest+11%197523
Great Basin-65%197464
Northern Rockies-28%198818
Boreal Hardwood Transition-86%196913
Prairie Hardwood Transition-18%198516
Southeastern Coastal Plain-28%197012
New England / Mid-Atlantic Coast+6%19708
Peninsular Florida-23%197617
Coastal California-25%197031
Sonoran and Mojave Deserts-87%19773
Gulf Coastal Prairie+19%197117

Caspian Tern Conservation Status

Our route-weighted index shows it up about 61% 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.