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

Northern Rough-winged Swallow Population Trend in California

All statesAerial insectivores

Northern Rough-winged Swallow in California has fallen sharply: down 54% on the route-weighted index since 1970.

-54%Since 1970TrendPercent 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 →
203Routes 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 →
56YearsYears surveyedNumber of years with at least one standard-protocol run in this geography. A longer record makes the trend more reliable.Full methodology →

Notable Northern Rough-winged Swallow Trends in CaliforniaNotable 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 →

Northern Rough-winged Swallow has fallen sharply in California: down 54% on the route-weighted index since 1970.

Northern Rough-winged Swallow Population Forecast in California

If the recent trend holds, Northern Rough-winged Swallow in California is projected to fall about 24% by 2029 — from 0.95 in 2024 to a central estimate of 0.72 (95% range 0.00–2.6). A 5-year backtest shows a typical error of ±33%, with 100% of held-out values landing inside the 95% band.

-24%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 →
0.72Projected 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 →
0.00–2.695% 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 →
±33%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, Northern Rough-winged Swallow in California is projected to fall about 24% by 2029 — from 0.95 in 2024 to a central estimate of 0.72 (95% range 0.00–2.6). A 5-year backtest shows a typical error of ±33%, 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 →
20250.900.002.8
20260.860.002.8
20270.810.002.7
20280.760.002.7
20290.720.002.6

Northern Rough-winged Swallow Survey Routes in California

Routes recording Northern Rough-winged Swallow in California.
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 →
Oilfields7720052005
Brawley4820101971
Orland4019921983
Collegeville3220021972
El Toro2319991973
Horse Creek2220191970
Parker Dam1820071973
Bakersfield1720231979
Palo Verde1620241973
Orange Cove1520121972
Coachella Cn1420131977
Blythe1419791973
Elizabeth Lk1420161972
Sisquoc1320141971
Fish Rock1220141969
Jofegan 21120242024
Athlone1120071978
Niland1020241973
Korbel1020211973
Glamis920181973
Havasu Lake920032003
Imperial Dam920101973
Creston920231972
Carrizo Pln920211970
Iron Gate920191988

Northern Rough-winged Swallow Population Trend in Other States

alabamaalaskaarizonaarkansascoloradoconnecticutdelawarefloridageorgiaidahoillinoisindianaiowakansaskentuckylouisianamainemarylandmassachusettsmichiganminnesotamississippimissourimontananebraskanevadanew-hampshirenew-jerseynew-mexiconew-yorknorth-carolinanorth-dakotaohiooklahomaoregonpennsylvaniarhode-islandsouth-carolinasouth-dakotatennesseetexasutahvermontvirginiawashingtonwest-virginiawisconsinwyoming

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