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

Swainson's Thrush In Sierra Nevada

All regionsSierra NevadaForest birds

Swainson's Thrush in Sierra Nevada has surged: up 90% on the route-weighted index since 1974.

+90%Since 1974TrendPercent 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 →
16Routes 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 →
38YearsYears 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 →

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 →

Swainson's Thrush has surged in Sierra Nevada: up 90% on the route-weighted index since 1974.

Swainson's Thrush In Sierra Nevada Population Forecast

If the recent trend holds, Swainson's Thrush in Sierra Nevada is projected to fall about 41% by 2029 — from 0.42 in 2024 to a central estimate of 0.25 (95% range 0.00–0.53). A 5-year backtest shows a typical error of ±68.1%, with 40% of held-out values landing inside the 95% band.

-41%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 →
0.25Projected 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 →
0.00–0.5395% 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 →
±68.1%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, Swainson's Thrush in Sierra Nevada is projected to fall about 41% by 2029 — from 0.42 in 2024 to a central estimate of 0.25 (95% range 0.00–0.53). A 5-year backtest shows a typical error of ±68.1%, with 40% of held-out values landing inside the 95% band.19712029
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 →
20250.240.000.52
20260.240.000.52
20270.240.000.53
20280.250.000.53
20290.250.000.53

Routes In Sierra Nevada

Routes recording Swainson's Thrush 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 →
LumberyardCALIFORNIA61989
Meadow ValleyCALIFORNIA52024
PlacervilleCALIFORNIA32024
Lassen ParkCALIFORNIA21979
WestvilleCALIFORNIA22021
Greenhorn MtCALIFORNIA21974
Silver CityCALIFORNIA22002
DardanelleCALIFORNIA11978
JohnsvilleCALIFORNIA12015
WoodfordsCALIFORNIA11983
Kings CanyonCALIFORNIA11989
Tuolumne GroveCALIFORNIA11994
Butte MeadowCALIFORNIA11995
RivertonCALIFORNIA12017
PaxtonCALIFORNIA12019
Pollock PinesCALIFORNIA12019

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