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Species · BCR 4 · BBS 2025 Release · 1966–2024

Arctic Tern In BCR 4

All regionsBCR 4Wetland birds

Arctic Tern in BCR 4 has collapsed: down 84% on the route-weighted index since 1978.

-84%Since 1978TrendPercent 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 →
41Routes 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 →
45YearsYears 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 →

Arctic Tern has collapsed in BCR 4: down 84% on the route-weighted index since 1978.

Arctic Tern In BCR 4 Population Forecast

If the recent trend holds, Arctic Tern in BCR 4 is projected to rise about 768% by 2029 — from 0.06 in 2024 to a central estimate of 0.49 (95% range 0.00–1.9). A 5-year backtest shows a typical error of ±1187.3%, with 100% of held-out values landing inside the 95% band.

+768%Change 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 →
0.49Projected 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 →
0.00–1.995% 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 →
±1187.3%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, Arctic Tern in BCR 4 is projected to rise about 768% by 2029 — from 0.06 in 2024 to a central estimate of 0.49 (95% range 0.00–1.9). A 5-year backtest shows a typical error of ±1187.3%, with 100% of held-out values landing inside the 95% band.19762029
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 →
20250.540.002.0
20260.530.002.0
20270.520.002.0
20280.500.002.0
20290.490.001.9

Routes In BCR 4

Routes recording Arctic Tern in BCR 4.
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 →
Seven LakesALASKA92023
Kenny LakeALASKA61990
Porcupine R.ALASKA52002
SourdoughALASKA42017
Tangle LakesALASKA41987
Mud RiverALASKA42013
Ft. RichrdsnALASKA42022
CohoeALASKA32018
Unalakleet RiverALASKA32017
ChistochinaALASKA21995
NorthwayALASKA22008
MaclarenALASKA22024
ToklatALASKA21999
HomerALASKA21978
KalifonskyALASKA22023
WillowALASKA21999
Bear CreekALASKA21991
Swan Lake RdALASKA22013
Lake LouiseALASKA22011
WasillaALASKA21983
Nicholai SlALASKA22002
PetersvilleALASKA22019
KachemakALASKA22006
Burma RoadALASKA22004
Hather CreekALASKA22017

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