BirdAnalyst
Species · BCR 15 · BBS 2026 Release · 1966–2025

Cassin's Vireo In Sierra Nevada

All regionsSierra NevadaForest birds

Cassin's Vireo in Sierra Nevada has edged up: up 13% on the route-weighted index since 1972.

+13%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 →
37Routes 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 →
55YearsYears 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 →

No notable trend signals for Cassin's Vireo in Sierra Nevada. See the full index history below.

Cassin's Vireo In Sierra Nevada Population Forecast

If the recent trend holds, Cassin's Vireo in Sierra Nevada is projected to rise about 31% by 2030 — from 6.2 in 2025 to a central estimate of 8.1 (95% range 5.4–11). A 5-year backtest shows a typical error of ±25.7%, with 100% of held-out values landing inside the 95% band.

+31%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 →
8.1Projected 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 →
5.4–1195% 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 →
±25.7%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, Cassin's Vireo in Sierra Nevada is projected to rise about 31% by 2030 — from 6.2 in 2025 to a central estimate of 8.1 (95% range 5.4–11). A 5-year backtest shows a typical error of ±25.7%, with 100% 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 →
20267.85.111
20277.95.211
20288.05.211
20298.05.311
20308.15.411

Routes In Sierra Nevada

Routes recording Cassin's Vireo in Sierra Nevada.
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 →
Butte MeadowCALIFORNIA262014
Forest Hill 2CALIFORNIA182005
Forest HillCALIFORNIA152025
GeneseeCALIFORNIA132024
RivertonCALIFORNIA122025
JohnsvilleCALIFORNIA112025
ChesterCALIFORNIA112017
Meadow ValleyCALIFORNIA112025
DownievilleCALIFORNIA102025
WestvilleCALIFORNIA92025
PlacervilleCALIFORNIA92025
StrawberryCALIFORNIA92019
Tuolumne GroveCALIFORNIA82025
Eagle LakeCALIFORNIA72025
Little TruckeeCALIFORNIA72025
Hat CreekCALIFORNIA52018
Last ChanceCALIFORNIA52019
Chaos CraterCALIFORNIA42019
PaxtonCALIFORNIA42025
ChilcootCALIFORNIA42024
Cottage SpgsCALIFORNIA31975
Bass LakeCALIFORNIA32018
LumberyardCALIFORNIA32025
GoumazCALIFORNIA32011
WawonaCALIFORNIA32025

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