BirdAnalyst
Species · Vermont · BBS 2025 Release · 1966–2024

Brown-headed Cowbird Population Trend in Vermont

All statesGeneralists

Brown-headed Cowbird in Vermont has collapsed: down 77% on the route-weighted index since 1968.

-77%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 →
26Routes 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 →
58YearsYears surveyedNumber of years with at least one standard-protocol run in this geography. A longer record makes the trend more reliable.Full methodology →

Notable Brown-headed Cowbird Trends in VermontNotable 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 →

Brown-headed Cowbird has collapsed in Vermont: down 77% on the route-weighted index since 1968.

Brown-headed Cowbird Population Forecast in Vermont

If the recent trend holds, Brown-headed Cowbird in Vermont is projected to fall about 18% by 2029 — from 1.7 in 2024 to a central estimate of 1.4 (95% range 0.00–5.9). A 5-year backtest shows a typical error of ±95.5%, with 100% of held-out values landing inside the 95% band.

-18%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 →
1.4Projected 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 →
0.00–5.995% 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 →
±95.5%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 Vermont is projected to fall about 18% by 2029 — from 1.7 in 2024 to a central estimate of 1.4 (95% range 0.00–5.9). A 5-year backtest shows a typical error of ±95.5%, with 100% of held-out values landing inside the 95% band.19662029
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 →
20251.80.006.3
20261.70.006.2
20271.60.006.1
20281.50.006.0
20291.40.005.9

Brown-headed Cowbird Survey Routes in Vermont

Routes recording Brown-headed Cowbird in Vermont.
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 →
Waterville1519801967
Marlboro820241966
Hinesburg819941966
Fletcher720241968
Grand Isle620241967
Shaftsbury320241966
North Pownal220221966
Landgrove220241966
S Reading220181966
S Wallingfrd220171966
East Haven220241966
Northfld Fls220161980
East Calais220181972
Colchester220211986
Stowe220221988
Bristol220181995
Stratton120221966
Gaysville120141966
Post Mills120241966
W Rutland120231966
St Johnsbury120241970
Middlesex120181968
Newbury120031986
Hardwick120131966
Greensboro120161967

Brown-headed Cowbird Population Trend in Other States

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