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

Fox Sparrow Population Trend in Colorado

All statesGeneralists

Fox Sparrow in Colorado has surged: up 395% on the route-weighted index since 1972.

+395%Since 1972TrendPercent 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 →
50Routes 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 →
50YearsYears surveyedNumber of years with at least one standard-protocol run in this geography. A longer record makes the trend more reliable.Full methodology →

Notable Fox Sparrow 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 →

Fox Sparrow has surged in Colorado: up 395% on the route-weighted index since 1972.

Fox Sparrow Population Forecast in Colorado

If the recent trend holds, Fox Sparrow in Colorado is projected to rise about 11% by 2029 — from 0.54 in 2024 to a central estimate of 0.59 (95% range 0.27–0.92). A 5-year backtest shows a typical error of ±52%, with 100% of held-out values landing inside the 95% band.

+11%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 →
0.59Projected 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 →
0.27–0.9295% 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 →
±52%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, Fox Sparrow in Colorado is projected to rise about 11% by 2029 — from 0.54 in 2024 to a central estimate of 0.59 (95% range 0.27–0.92). A 5-year backtest shows a typical error of ±52%, 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 →
20250.570.250.89
20260.580.260.90
20270.580.260.90
20280.590.270.91
20290.590.270.92

Fox Sparrow Survey Routes in Colorado

Routes recording Fox Sparrow 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 →
Tincup1320241999
Weston Pass 2620242001
Dolores Riv620241988
Red Cliff520241989
Castleton520242004
Ragged Mtn.520191999
Great Divide319771977
Buford320221992
Lost Lake320241999
Weston Pass320001994
Fox Creek320112008
Rifle Falls320212001
Mount Evans220091996
Colona220121980
Parlin220231968
Wilson Creek220241992
Uncompahgre220231988
Doyleville220232010
Lake City220031988
Como220241996
Marshall Pas220111995
Buffalo Park220232007
Flattops220062006
Thomasville220182001
Nucla220242014

Fox Sparrow Population Trend in Other States

alaskacaliforniaidahomainemontananevadaoregonutahwashingtonwyoming

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