BirdAnalyst
Species · Colorado · BBS 2026 Release · 1966–2025

Western Tanager Population Trend in Colorado

All statesForest birds

Western Tanager in Colorado has surged: up 133% on the route-weighted index since 1970.

+133%Since 1970TrendPercent 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 →
93Routes 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 →
57YearsYears surveyedNumber of years with at least one standard-protocol run in this geography. A longer record makes the trend more reliable.Full methodology →

Notable Western Tanager Trends in ColoradoNotable 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 increasecomputed 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 →

Western Tanager has surged in Colorado: up 133% on the route-weighted index since 1970.

Western Tanager Population Forecast in Colorado

If the recent trend holds, Western Tanager in Colorado is projected to fall about 18% by 2030 — from 5.6 in 2025 to a central estimate of 4.6 (95% range 3.0–6.2). A 5-year backtest shows a typical error of ±21.5%, with 60% of held-out values landing inside the 95% band.

-18%Change 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 →
4.6Projected 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 →
3.0–6.295% 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 →
±21.5%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, Western Tanager in Colorado is projected to fall about 18% by 2030 — from 5.6 in 2025 to a central estimate of 4.6 (95% range 3.0–6.2). A 5-year backtest shows a typical error of ±21.5%, with 60% of held-out values landing inside the 95% band.19682030
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 →
20264.32.85.9
20274.42.86.0
20284.52.96.0
20294.52.96.1
20304.63.06.2

Western Tanager Survey Routes in Colorado

Routes recording Western Tanager in Colorado.
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 →
Dolores Riv3620251988
Mcphee Res.3320251996
Heeney 22920252025
Cokedale2620251995
South Fork2520251994
Baxter Pass2320241994
Gribbles Prk2320251999
Dunckley Pas2220251992
Heeney2220192017
Douglas Pass2120241987
Cheesman Lk2120251969
Deadman Rd.1920251992
Comanche Pk1920241994
Buffalo Park1720251992
Blackhead Pk1620251991
Groundhog Rs1620251995
Marshall Pas1620191995
Gold Hill 21520252018
Tarryall1420251988
Uncompahgre1420251988
Haycamp Mesa1420251998
Pinon1320251992
Aspen1220251979
Castleton1220251988
Flattops1220251992

Western Tanager Population Trend in Other States

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Source: USGS North American Breeding Bird Survey, retrieved 2026-08-14.