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

Willow Flycatcher Population Trend in Colorado

All statesAerial insectivores

Willow Flycatcher in Colorado has fallen sharply: down 61% on the route-weighted index since 1970.

-61%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 →
41Routes 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 →
56YearsYears surveyedNumber of years with at least one standard-protocol run in this geography. A longer record makes the trend more reliable.Full methodology →

Notable Willow Flycatcher 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 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 →

Willow Flycatcher has fallen sharply in Colorado: down 61% on the route-weighted index since 1970.

Willow Flycatcher Population Forecast in Colorado

If the recent trend holds, Willow Flycatcher in Colorado is projected to stay roughly flat through 2029, near 0.18 (95% range 0.00–0.62). A 5-year backtest shows a typical error of ±76%, with 100% of held-out values landing inside the 95% band.

+3%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 →
0.18Projected 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 →
0.00–0.6295% 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 →
±76%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, Willow Flycatcher in Colorado is projected to stay roughly flat through 2029, near 0.18 (95% range 0.00–0.62). A 5-year backtest shows a typical error of ±76%, 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 →
20250.200.000.64
20260.200.000.64
20270.190.000.63
20280.190.000.62
20290.180.000.62

Willow Flycatcher Survey Routes in Colorado

Routes recording Willow Flycatcher 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 →
Buford520241972
Stillwater Pass520072001
Tarryall320051989
Steamboat L.320241996
Ragged Mtn.320191999
Yampa220231969
Harmony219981979
Lost Lake220051990
Castleton220241988
Comanche Pk220142006
Alamosa220242002
Thomasville220131992
Groundhog Rs220051998
Maybell120171974
Aspen120241992
Cheesman Lk120092009
Abarr119841977
Delta119911991
Colona119851985
Parlin120221968
Dolores119821982
Falfa119711971
Wray Gulch120082008
Walden120241991
Red Cliff120231989

Willow Flycatcher Population Trend in Other States

alaskaarizonaarkansascaliforniaconnecticutdelawaregeorgiaidahoillinoisindianaiowakansaskentuckymainemarylandmassachusettsmichiganminnesotamissourimontananebraskanevadanew-hampshirenew-jerseynew-mexiconew-yorknorth-carolinanorth-dakotaohiooklahomaoregonpennsylvaniarhode-islandsouth-dakotatennesseetexasutahvermontvirginiawashingtonwest-virginiawisconsinwyoming

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