BirdAnalyst
Species · BBS 2025 Release · 1966–2024

Brewer's Sparrow

PasserellidaeArid-land birdsSpizella breweri

Brewer's Sparrow has surged: up 504% on the route-weighted index since 1969.

+504%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 →
768RoutesSurvey 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 Brewer's Sparrow

The Brewer's Sparrow (Spizella breweri) is a North American member of the New World Sparrows (Passerellidae). In this analysis it is grouped with the arid-land birds.

Size
4.5–7.5 in long (12–19 cm) — a small songbird (typical for the family)
Habitat
Deserts, dry scrub and brushland of the Southwest.
Diet
Seeds, insects and cactus fruit of arid-land plants.
Range
Recorded on 768 Breeding Bird Survey routes across 17 states, most concentrated in the Great Basin.
Family
Passerellidae · Arid-land birds

Notable Brewer's Sparrow TrendsNotable 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 increasecomputed 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 surged in surveyed states: up 504% on the route-weighted index since 1969.

Brewer's Sparrow Population Forecast

If the recent trend holds, Brewer's Sparrow is projected to stay roughly flat through 2029, near 2.6 (95% range 1.7–3.5). A 5-year backtest shows a typical error of ±34.2%, with 80% of held-out values landing inside the 95% band.

+2%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 →
2.6Projected 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 →
1.7–3.595% 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 →
±34.2%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 is projected to stay roughly flat through 2029, near 2.6 (95% range 1.7–3.5). A 5-year backtest shows a typical error of ±34.2%, with 80% 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 →
20252.51.63.4
20262.51.63.4
20272.51.63.5
20282.61.63.5
20292.61.73.5

Where the Brewer's Sparrow Is Detected

BBS routes recording Brewer's Sparrow, sized by most recent count.

Brewer's Sparrow Population Trend by State

Brewer's Sparrow 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 →
Arizona-78%197319
California+138%197164
Colorado+103%1970117
Idaho-13%197046
Kansasinsufficient datan/a2
Montana-35%197084
Nebraska-71%19695
Nevada+88%197050
New Mexico-3%197720
North Dakotainsufficient datan/a2
Oklahomainsufficient datan/a1
Oregon+143%197076
South Dakota-20%19795
Texasinsufficient datan/a1
Utah+45%1971108
Washington+302%197037
Wyoming+46%1970131

Brewer's Sparrow Population Trend by Region

Bird Conservation Regions are the ecological unit for trends.

Brewer's Sparrow 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 →
Northern Pacific Rainforest-60%19783
Great Basin+50%1970217
Northern Rockies+140%1970169
Prairie Potholes+103%197219
Sierra Nevada-55%197114
Southern Rockies / Colorado Plateau+106%1970182
Badlands and Prairies-7%197075
Shortgrass Prairie-72%196945
Coastal California-94%197110
Sonoran and Mojave Deserts-80%197225
Sierra Madre Occidental-96%19895

Brewer's Sparrow Conservation Status

Our route-weighted index shows it up about 504% 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.