BirdAnalyst
Species · BCR 15 · BBS 2025 Release · 1966–2024

Brown-headed Cowbird In Sierra Nevada

All regionsSierra NevadaGeneralists

Brown-headed Cowbird in Sierra Nevada has declined: down 30% on the route-weighted index since 1970.

-30%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 →
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 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 fall about 33% by 2029 — from 4.9 in 2024 to a central estimate of 3.3 (95% range 1.3–5.4). A 5-year backtest shows a typical error of ±28.7%, with 100% of held-out values landing inside the 95% band.

-33%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 →
3.3Projected 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 →
1.3–5.495% 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 →
±28.7%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, Brown-headed Cowbird in Sierra Nevada is projected to fall about 33% by 2029 — from 4.9 in 2024 to a central estimate of 3.3 (95% range 1.3–5.4). A 5-year backtest shows a typical error of ±28.7%, 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 →
20253.41.45.4
20263.41.45.4
20273.41.45.4
20283.41.35.4
20293.31.35.4

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
SattleyCALIFORNIA192024
GeneseeCALIFORNIA142024
Eagle LakeCALIFORNIA112024
Bass LakeCALIFORNIA112019
Last ChanceCALIFORNIA82019
Tahoe NfCALIFORNIA61994
Greenhorn MtCALIFORNIA52008
Higgins CornCALIFORNIA52024
WawonaCALIFORNIA52024
Butte MeadowCALIFORNIA42014
GoumazCALIFORNIA42011
Silver CityCALIFORNIA32013
Tuolumne GroveCALIFORNIA32024
RivertonCALIFORNIA32012
Hat CreekCALIFORNIA32016
PaxtonCALIFORNIA32024
Pollock PinesCALIFORNIA32024
KernvilleCALIFORNIA32008
DownievilleCALIFORNIA22024
LakeshoreCALIFORNIA22024
PlacervilleCALIFORNIA22024
CoultervilleCALIFORNIA22018
StrawberryCALIFORNIA22010
Lassen ParkCALIFORNIA11986

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