BirdAnalyst
Species · Montana · BBS 2025 Release · 1966–2024

Common Tern Population Trend in Montana

All statesWetland birds

Common Tern in Montana has collapsed: down 83% on the route-weighted index since 1976.

-83%Since 1976TrendPercent 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 →
10Routes In StateSurvey routesHow many standard-protocol BBS routes contributed counts. More routes means a steadier, better-sampled index; very thin coverage is suppressed.Full methodology →
19YearsYears surveyedNumber of years with at least one standard-protocol run in this geography. A longer record makes the trend more reliable.Full methodology →

Notable Common Tern Trends in MontanaNotable 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 Montana: down 83% on the route-weighted index since 1976.

Common Tern Population Forecast in Montana

If the recent trend holds, Common Tern in Montana 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 ±231.2%, 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 →
±231.2%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, Common Tern in Montana 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 ±231.2%, with 100% of held-out values landing inside the 95% band.19682029
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

Common Tern Survey Routes in Montana

Routes recording Common Tern in Montana.
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 →
St Mary419681968
Ester Lake320162016
Great Falls220031973
Brusett219861983
Jordan220001968
Virgelle119901990
Cleveland120132013
Pablo Res.120242024
Augusta120131976
Chinook120182018

Common Tern Population Trend in Other States

alabamaalaskaconnecticutdelawarefloridaidahoindianalouisianamainemarylandmassachusettsmichiganminnesotanew-jerseynew-yorknorth-carolinanorth-dakotaohiorhode-islandsouth-dakotatexasvermontvirginiawashingtonwisconsinwyoming

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