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

Brewer's Sparrow Population Trend in Arizona

All statesGeneralists

Brewer's Sparrow in Arizona has collapsed: down 78% on the route-weighted index since 1973.

-78%Since 1973TrendPercent 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 →
19Routes 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 →
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 Brewer's Sparrow Trends in ArizonaNotable 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 →

Brewer's Sparrow has collapsed in Arizona: down 78% on the route-weighted index since 1973.

Brewer's Sparrow Population Forecast in Arizona

If the recent trend holds, Brewer's Sparrow in Arizona is projected to rise about 63% by 2029 — from 0.06 in 2024 to a central estimate of 0.09 (95% range 0.00–1.4). A 5-year backtest shows a typical error of ±66.9%, with 100% of held-out values landing inside the 95% band.

+63%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 →
0.00–1.495% 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 →
±66.9%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, Brewer's Sparrow in Arizona is projected to rise about 63% by 2029 — from 0.06 in 2024 to a central estimate of 0.09 (95% range 0.00–1.4). A 5-year backtest shows a typical error of ±66.9%, with 100% of held-out values landing inside the 95% band.19692029
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 →
20250.150.001.5
20260.140.001.5
20270.120.001.4
20280.110.001.4
20290.090.001.4

Brewer's Sparrow Survey Routes in Arizona

Routes recording Brewer's Sparrow in Arizona.
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 →
Pomerene1019741974
Sunizona919881974
House Rock820211971
Mt Trumbull619801977
Black Mesa619951988
Navajo Trail620231995
The Gap419731973
Toroweap320231995
Alamo Res.319921992
Oraibi220192018
Page220191995
Round Rock119691969
Sawmill119961990
Cow Springs120222019
Antares120242004
Skull Valley120212021
Pinetop120181993
Tsaile120192018
Clay Spring120241989

Brewer's Sparrow Population Trend in Other States

californiacoloradoidahokansasmontananebraskanevadanew-mexiconorth-dakotaoklahomaoregonsouth-dakotatexasutahwashingtonwyoming

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