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Species · Massachusetts · BBS 2026 Release · 1966–2025

Chestnut-sided Warbler Population Trend in Massachusetts

All statesForest birds

Chestnut-sided Warbler in Massachusetts has risen sharply: up 58% on the route-weighted index since 1968.

+58%Since 1968TrendPercent 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 →
28Routes In StateSurvey routesHow many standard-protocol BBS routes contributed counts. More routes means a steadier, better-sampled index; very thin coverage is suppressed.Full methodology →
59YearsYears surveyedNumber of years with at least one standard-protocol run in this geography. A longer record makes the trend more reliable.Full methodology →

Notable Chestnut-sided Warbler Trends in MassachusettsNotable 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 →

Chestnut-sided Warbler has risen sharply in Massachusetts: up 58% on the route-weighted index since 1968.

Chestnut-sided Warbler Population Forecast in Massachusetts

If the recent trend holds, Chestnut-sided Warbler in Massachusetts is projected to fall about 39% by 2030 — from 6.7 in 2025 to a central estimate of 4.0 (95% range 1.3–6.8). A 5-year backtest shows a typical error of ±40%, with 60% of held-out values landing inside the 95% band.

-39%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 →
4.0Projected 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 →
1.3–6.895% 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 →
±40%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, Chestnut-sided Warbler in Massachusetts is projected to fall about 39% by 2030 — from 6.7 in 2025 to a central estimate of 4.0 (95% range 1.3–6.8). A 5-year backtest shows a typical error of ±40%, with 60% of held-out values landing inside the 95% band.19662030
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 →
20264.21.56.9
20274.21.46.9
20284.11.46.9
20294.11.46.8
20304.01.36.8

Chestnut-sided Warbler Survey Routes in Massachusetts

Routes recording Chestnut-sided Warbler in Massachusetts.
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 →
Monterey2620252019
Cummington 22220252015
Pittsfield1920161967
Chesterfield1720251967
N Orange1620251968
Cummington1520141968
Ware River1420221993
S Barre1420251968
Sheffield1020221969
Hancock820151997
Belchertown620251967
Princeton519761969
Cheshire519941969
Holden320251977
N. Andover320041995
Marion219771969
Wellfleet219871971
Maynard220221967
Littleton220241967
E Pepperell219931966
Warren220091968
Warren 2220252010
E Dennis119871970
Chilmark119711969
Prattville120041966

Chestnut-sided Warbler Population Trend in Other States

alabamaarkansascoloradoconnecticutgeorgiaillinoisindianaiowakansaskentuckymainemarylandmichiganminnesotanevadanew-hampshirenew-jerseynew-yorknorth-carolinanorth-dakotaohiopennsylvaniarhode-islandtennesseevermontvirginiawest-virginiawisconsinwyoming

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