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

Brown-headed Cowbird In Sierra Nevada

All regionsSierra NevadaGeneralists

Brown-headed Cowbird in Sierra Nevada has edged down: down 23% on the route-weighted index since 1970.

-23%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 →
39Routes 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 →
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 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 Brown-headed Cowbird in Sierra Nevada. See the full index history below.

Brown-headed Cowbird In Sierra Nevada Population Forecast

If the recent trend holds, Brown-headed Cowbird in Sierra Nevada is projected to stay roughly flat through 2030, near 3.3 (95% range 1.3–5.3). A 5-year backtest shows a typical error of ±25.5%, with 100% of held-out values landing inside the 95% band.

+6%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 →
3.3Projected 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 →
1.3–5.395% 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 →
±25.5%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, Brown-headed Cowbird in Sierra Nevada is projected to stay roughly flat through 2030, near 3.3 (95% range 1.3–5.3). A 5-year backtest shows a typical error of ±25.5%, 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 →
20263.41.45.4
20273.41.45.4
20283.31.35.3
20293.31.35.3
20303.31.35.3

Routes In Sierra Nevada

Routes recording Brown-headed Cowbird 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 →
ChilcootCALIFORNIA222024
GeneseeCALIFORNIA142024
PaxtonCALIFORNIA122025
Bass LakeCALIFORNIA112019
Eagle LakeCALIFORNIA92025
Last ChanceCALIFORNIA82019
SattleyCALIFORNIA72025
Tahoe NfCALIFORNIA61994
Greenhorn MtCALIFORNIA52008
PlacervilleCALIFORNIA52025
Butte MeadowCALIFORNIA42014
DownievilleCALIFORNIA42025
GoumazCALIFORNIA42011
WestvilleCALIFORNIA32025
Silver CityCALIFORNIA32013
RivertonCALIFORNIA32025
Hat CreekCALIFORNIA32016
Meadow ValleyCALIFORNIA32025
Pollock PinesCALIFORNIA32024
WawonaCALIFORNIA32025
KernvilleCALIFORNIA32008
WoodfordsCALIFORNIA22025
Tuolumne GroveCALIFORNIA22025
LakeshoreCALIFORNIA22024
CoultervilleCALIFORNIA22018

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