BirdAnalyst
Species · BCR 4 · BBS 2025 Release · 1966–2024

Tree Swallow In BCR 4

All regionsBCR 4Aerial insectivores

Tree Swallow in BCR 4 has collapsed: down 83% on the route-weighted index since 1976.

-83%Since 1976TrendPercent 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 →
59Routes In RegionSurvey routesHow many standard-protocol BBS routes contributed counts. More routes means a steadier, better-sampled index; very thin coverage is suppressed.Full methodology →
47YearsYears surveyedNumber of years with at least one standard-protocol run in this geography. A longer record makes the trend more reliable.Full methodology →

Notable SignalsNotable 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 →

Tree Swallow has collapsed in BCR 4: down 83% on the route-weighted index since 1976.

Tree Swallow In BCR 4 Population Forecast

If the recent trend holds, Tree Swallow in BCR 4 is projected to fall about 100% by 2029 — from 1.3 in 2024 to a central estimate of 0.00 (95% range 0.00–5.4). A 5-year backtest shows a typical error of ±119.8%, with 100% of held-out values landing inside the 95% band.

-100%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 →
0.00Projected 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 →
0.00–5.495% 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 →
±119.8%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, Tree Swallow in BCR 4 is projected to fall about 100% by 2029 — from 1.3 in 2024 to a central estimate of 0.00 (95% range 0.00–5.4). A 5-year backtest shows a typical error of ±119.8%, with 100% of held-out values landing inside the 95% band.19682029
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 →
20250.140.005.5
20260.010.005.4
20270.000.005.4
20280.000.005.4
20290.000.005.4

Routes In BCR 4

Routes recording Tree Swallow in BCR 4.
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 →
WasillaALASKA421983
CottonwoodALASKA361990
Skilak LakeALASKA211985
Goose BayALASKA201982
Unalakleet RiverALASKA122023
Hather CreekALASKA112024
Galena (Short)ALASKA112024
MatanuskaALASKA101983
Chena Hot SpALASKA91990
WillowALASKA72024
KuskulanaALASKA62023
SlanaALASKA52022
HomerALASKA51982
L SalchaALASKA52008
Murphy DomeALASKA52017
NorthwayALASKA42019
KalifonskyALASKA42023
SourdoughALASKA42016
Lake LouiseALASKA42008
Tangle LakesALASKA41987
Mud RiverALASKA42024
MonahanALASKA32018
TonsinaALASKA32021
Bear CreekALASKA31991
Anchor RiverALASKA32023

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