BirdAnalyst
Species · BCR 9 · BBS 2025 Release · 1966–2024

Caspian Tern In Great Basin

All regionsGreat BasinWetland birds

Caspian Tern in Great Basin has fallen sharply: down 67% on the route-weighted index since 1974.

-67%Since 1974TrendPercent 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 →
63Routes In RegionSurvey routesHow many standard-protocol BBS routes contributed counts. More routes means a steadier, better-sampled index; very thin coverage is suppressed.Full methodology →
52YearsYears surveyedNumber of years with at least one standard-protocol run in this geography. A longer record makes the trend more reliable.Full methodology →

Notable SignalsNotable 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 →

Caspian Tern has fallen sharply in Great Basin: down 67% on the route-weighted index since 1974.

Caspian Tern In Great Basin Population Forecast

If the recent trend holds, Caspian Tern in Great Basin is projected to stay roughly flat through 2029, near 0.45 (95% range 0.00–0.97). A 5-year backtest shows a typical error of ±873.3%, with 40% 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 →
0.45Projected 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 →
0.00–0.9795% 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 →
±873.3%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 in Great Basin is projected to stay roughly flat through 2029, near 0.45 (95% range 0.00–0.97). A 5-year backtest shows a typical error of ±873.3%, with 40% of held-out values landing inside the 95% band.19722029
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 →
20250.450.000.96
20260.450.000.97
20270.450.000.97
20280.450.000.97
20290.450.000.97

Routes In Great Basin

Routes recording Caspian Tern in Great Basin.
Recent countThe raw number of individuals recorded on this route in its most recent survey year. A single-route tally, not a trend.Full methodology →
Iron GateCALIFORNIA792019
DorrisCALIFORNIA112019
TonasketWASHINGTON91993
Ruby ValleyNEVADA81999
Harney LakeOREGON62001
IngallsCALIFORNIA51999
CallaoUTAH42023
Moses LakeWASHINGTON42011
L. WenatcheeWASHINGTON42003
CedarvilleCALIFORNIA31998
Kyle CanyonIDAHO31986
NixonNEVADA32022
Bald Mtn.NEVADA32010
OthelloWASHINGTON31991
Honey LakeCALIFORNIA21976
Clear Lk ResCALIFORNIA22018
AcequiaIDAHO22002
UmatillaOREGON22022
Malheur NwrOREGON21997
LeamingtonUTAH22016
QuincyWASHINGTON22012
EwanWASHINGTON22019
EllensburgWASHINGTON22009
OdessaWASHINGTON22007
Lake ChelanWASHINGTON21996

Source: USGS North American Breeding Bird Survey, retrieved 2026-05-22.