BirdAnalyst
Species · BBS 2025 Release · 1966–2024

Arctic Warbler

PhylloscopidaeForest birdsPhylloscopus borealis

Arctic Warbler has increased: up 27% on the route-weighted index since 1984.

+27%Since 1984TrendPercent 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 →
41RoutesSurvey routesHow many standard-protocol BBS routes contributed counts. More routes means a steadier, better-sampled index; very thin coverage is suppressed.Full methodology →
40Years 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 Arctic Warbler

The Arctic Warbler (Phylloscopus borealis) is a North American member of the Leaf Warblers (Phylloscopidae). In this analysis it is grouped with the forest birds.

Size
4–5 in long (10–13 cm) — a tiny 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 41 Breeding Bird Survey routes across 1 state, most concentrated in the BCR 4.
Family
Phylloscopidae · Forest birds

Notable Arctic 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 Arctic Warbler. See the full index history below.

Arctic Warbler Population Forecast

If the recent trend holds, Arctic Warbler is projected to rise about 11% by 2029 — from 0.08 in 2024 to a central estimate of 0.09 (95% range 0.01–0.17). A 5-year backtest shows a typical error of ±51.6%, with 100% of held-out values landing inside the 95% band.

+11%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 →
0.09Projected 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 →
0.01–0.1795% 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 →
±51.6%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, Arctic Warbler is projected to rise about 11% by 2029 — from 0.08 in 2024 to a central estimate of 0.09 (95% range 0.01–0.17). A 5-year backtest shows a typical error of ±51.6%, with 100% of held-out values landing inside the 95% band.19822029
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 →
20250.090.010.17
20260.090.010.17
20270.090.010.17
20280.090.010.17
20290.090.010.17

Where the Arctic Warbler Is Detected

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

Arctic Warbler Population Trend by State

Arctic 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 →
Alaska-49%198441

Arctic Warbler Population Trend by Region

Bird Conservation Regions are the ecological unit for trends.

Arctic 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 →
BCR 2-36%199414
BCR 3+24%19983
BCR 4-56%198422

Arctic Warbler Conservation Status

Our route-weighted index shows it up about 27% since 1984.

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