BirdAnalyst
Species · BBS 2025 Release · 1966–2024

Connecticut Warbler

ParulidaeForest birdsOporornis agilis

Connecticut Warbler has declined: down 36% on the route-weighted index since 1969.

-36%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 →
75RoutesSurvey routesHow many standard-protocol BBS routes contributed counts. More routes means a steadier, better-sampled index; very thin coverage is suppressed.Full methodology →
57Years SurveyedYears surveyedNumber of years with at least one standard-protocol run in this geography. A longer record makes the trend more reliable.Full methodology →

About the Connecticut Warbler

The Connecticut Warbler (Oporornis agilis) is a North American member of the Wood-Warblers (Parulidae). In this analysis it is grouped with the forest birds.

Size
4.5–5.5 in long (11–14 cm) — a small, active songbird (typical for the family)
Habitat
Woodlands and forest edges, including wooded suburbs and parks.
Diet
Insects and spiders gleaned from foliage and bark, with seeds and berries in season.
Range
Recorded on 75 Breeding Bird Survey routes across 4 states, most concentrated in the Boreal Hardwood Transition.
Family
Parulidae · Forest birds

Notable Connecticut Warbler TrendsNotable signalsLong-arc shifts the engine flags automatically — sustained declines or increases large enough to stand out from year-to-year noise.Full methodology →

No notable trend signals for Connecticut Warbler. See the full index history below.

Connecticut Warbler Population Forecast

If the recent trend holds, Connecticut Warbler is projected to stay roughly flat through 2029, near 0.01 (95% range 0.00–0.02). A 5-year backtest shows a typical error of ±232.3%, with 100% of held-out values landing inside the 95% band.

n/aChange 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 →
0.01Projected 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 →
0.00–0.0295% 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 →
±232.3%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, Connecticut Warbler is projected to stay roughly flat through 2029, near 0.01 (95% range 0.00–0.02). A 5-year backtest shows a typical error of ±232.3%, with 100% of held-out values landing inside the 95% band.19672029
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 →
20250.010.000.02
20260.010.000.02
20270.010.000.02
20280.010.000.02
20290.010.000.02

Where the Connecticut Warbler Is Detected

BBS routes recording Connecticut Warbler, sized by most recent count.

Connecticut Warbler Population Trend by State

Connecticut Warbler population trend by state.
TrendPercent 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 →Baseline yearThe first year of the smoothed window the trend is measured from. An earlier baseline means a longer record stands behind the number.Full methodology →Survey routesHow many standard-protocol BBS routes contributed counts. More routes means a steadier, better-sampled index; very thin coverage is suppressed.Full methodology →
Michigan+23%198017
Minnesota-32%197031
New Yorkinsufficient datan/a1
Wisconsin-37%196926

Connecticut Warbler Population Trend by Region

Bird Conservation Regions are the ecological unit for trends.

Connecticut Warbler population trend by Bird Conservation Region.
TrendPercent 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 →Baseline yearThe first year of the smoothed window the trend is measured from. An earlier baseline means a longer record stands behind the number.Full methodology →Survey routesHow many standard-protocol BBS routes contributed counts. More routes means a steadier, better-sampled index; very thin coverage is suppressed.Full methodology →
Boreal Hardwood Transition-25%196968

Connecticut Warbler Conservation Status

Our route-weighted index shows it down about 36% since 1969.

Source: USGS North American Breeding Bird Survey, retrieved 2026-05-22. Trend is a route-weighted relative-abundance index, not an absolute population.