BirdAnalyst
Species · BCR 10 · BBS 2025 Release · 1966–2024

Forster's Tern In Northern Rockies

All regionsNorthern RockiesWetland birds

Forster's Tern in Northern Rockies has fallen sharply: down 55% on the route-weighted index since 1981.

-55%Since 1981TrendPercent 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 →
16Routes 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 →
39YearsYears 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 →

Forster's Tern has fallen sharply in Northern Rockies: down 55% on the route-weighted index since 1981.

Forster's Tern In Northern Rockies Population Forecast

If the recent trend holds, Forster's Tern in Northern Rockies is projected to stay roughly flat through 2029, near 0.04 (95% range 0.00–0.11). A 5-year backtest shows a typical error of ±182%, 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 →
0.00–0.1195% 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 →
±182%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, Forster's Tern in Northern Rockies is projected to stay roughly flat through 2029, near 0.04 (95% range 0.00–0.11). A 5-year backtest shows a typical error of ±182%, with 100% of held-out values landing inside the 95% band.19792029
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 →
20250.040.000.12
20260.040.000.12
20270.040.000.12
20280.040.000.11
20290.040.000.11

Routes In Northern Rockies

Routes recording Forster's Tern in Northern Rockies.
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 →
Neponset ResUTAH72018
MidvaleWYOMING61996
Red RockMONTANA41994
RandolphUTAH32024
KalispellMONTANA21990
AugustaMONTANA21982
Pablo Res.MONTANA22012
AlpineWYOMING21999
CentervilleIDAHO12011
Crane CreekIDAHO11989
FeathervilleIDAHO12010
Saleratus CrUTAH12003
NowoodWYOMING12000
FontenelleWYOMING12017
HarmonyWYOMING12023
SeedskadeeWYOMING12014

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