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Species · New Hampshire · BBS 2025 Release · 1966–2024

Cape May Warbler Population Trend in New Hampshire

All statesForest birds

Cape May Warbler in New Hampshire has fallen sharply: down 66% on the route-weighted index since 1969.

-66%Since 1969TrendPercent 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 →
12Routes 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 →
32YearsYears surveyedNumber of years with at least one standard-protocol run in this geography. A longer record makes the trend more reliable.Full methodology →

Notable Cape May Warbler Trends in New HampshireNotable 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 declinecomputed 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 →

Cape May Warbler has fallen sharply in New Hampshire: down 66% on the route-weighted index since 1969.

Cape May Warbler Population Forecast in New Hampshire

If the recent trend holds, Cape May Warbler in New Hampshire is projected to fall about 68% by 2028 — from 0.09 in 2023 to a central estimate of 0.03 (95% range 0.00–0.15). A 5-year backtest shows a typical error of ±65.6%, with 100% of held-out values landing inside the 95% band.

-68%Change by 2028TrendPercent 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 →
0.03Projected 2028 indexProjected indexThe central forecast of the abundance index if the recent trend continues. A projection of the current trajectory, not a prediction.Full methodology →
0.00–0.1595% 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 →
±65.6%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, Cape May Warbler in New Hampshire is projected to fall about 68% by 2028 — from 0.09 in 2023 to a central estimate of 0.03 (95% range 0.00–0.15). A 5-year backtest shows a typical error of ±65.6%, with 100% of held-out values landing inside the 95% band.19672028
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 →
20240.040.000.15
20250.030.000.15
20260.030.000.15
20270.030.000.15
20280.030.000.15

Cape May Warbler Survey Routes in New Hampshire

Routes recording Cape May Warbler in New Hampshire.
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 →
Milan219971983
Clarksville220231967
Fitzwilliam119821971
Gilmantn I W119981998
Mt Chocorua119761976
Crawford Not119751967
Jefferson Hl119691968
Franconia119821974
Stratford119791979
Dixvil Notch120161976
Glen120021993
Dixville Notch 2120192019

Cape May Warbler Population Trend in Other States

mainemichiganminnesotanew-yorkvermontwisconsin

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