BirdAnalyst
Species · BCR 32 · BBS 2026 Release · 1966–2025

Marsh Wren In Coastal California

All regionsCoastal CaliforniaForest birds

Marsh Wren in Coastal California has surged: up 11× on the route-weighted index since 1973.

11×Since 1973TrendPercent 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 →
26Routes 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 →
54YearsYears 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 →

Marsh Wren has surged in Coastal California: up 11× on the route-weighted index since 1973.

Marsh Wren In Coastal California Population Forecast

If the recent trend holds, Marsh Wren in Coastal California is projected to fall about 41% by 2030 — from 1.8 in 2025 to a central estimate of 1.1 (95% range 0.30–1.8). A 5-year backtest shows a typical error of ±36.6%, with 80% of held-out values landing inside the 95% band.

-41%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 →
1.1Projected 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 →
0.30–1.895% 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 →
±36.6%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, Marsh Wren in Coastal California is projected to fall about 41% by 2030 — from 1.8 in 2025 to a central estimate of 1.1 (95% range 0.30–1.8). A 5-year backtest shows a typical error of ±36.6%, with 80% of held-out values landing inside the 95% band.19712030
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 →
20261.00.251.8
20271.00.261.8
20281.00.281.8
20291.10.291.8
20301.10.301.8

Routes In Coastal California

Routes recording Marsh Wren in Coastal California.
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 →
Staten Is.CALIFORNIA362025
Ora LomaCALIFORNIA162025
GlennCALIFORNIA132025
ShafterCALIFORNIA51989
Cp. PendletonCALIFORNIA32003
TranquillityCALIFORNIA32004
Jofegan 2CALIFORNIA32025
PowayCALIFORNIA21980
ArvinCALIFORNIA21988
AtwaterCALIFORNIA22012
WestleyCALIFORNIA22014
ZamoraCALIFORNIA22003
CoyoteCALIFORNIA21984
Red BluffCALIFORNIA11992
PenningtonCALIFORNIA12023
Harbor LakeCALIFORNIA11991
MorenoCALIFORNIA12022
HollisterCALIFORNIA12005
Point ReyesCALIFORNIA12025
OrlandCALIFORNIA12008
FairfaxCALIFORNIA12010
OrovilleCALIFORNIA12024
Bartlett SpsCALIFORNIA11975
JofeganCALIFORNIA12023
Buena VistaCALIFORNIA12017

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