BirdAnalyst
Species · BBS 2025 Release · 1966–2024

Bronzed Cowbird

IcteridaeGeneralistsMolothrus aeneus

Bronzed Cowbird has held roughly steady: up 5% on the route-weighted index since 1969.

+5%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 →
147RoutesSurvey 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 Bronzed Cowbird

The Bronzed Cowbird (Molothrus aeneus) is a North American member of the Blackbirds & Orioles (Icteridae). In this analysis it is grouped with the generalists.

Size
6.5–17 in long (16–43 cm) — a small to medium songbird (typical for the family)
Habitat
A broad range of open and wooded habitats, often near people.
Diet
An opportunistic mix of insects, seeds, fruit and scraps.
Range
Recorded on 147 Breeding Bird Survey routes across 7 states, most concentrated in the Chihuahuan Desert.
Family
Icteridae · Generalists

Notable Bronzed Cowbird 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 Bronzed Cowbird. See the full index history below.

Bronzed Cowbird Population Forecast

If the recent trend holds, Bronzed Cowbird is projected to rise about 33% by 2029 — from 0.07 in 2024 to a central estimate of 0.09 (95% range 0.01–0.18). A 5-year backtest shows a typical error of ±61.5%, with 100% of held-out values landing inside the 95% band.

+33%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 →
0.01–0.1895% 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 →
±61.5%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, Bronzed Cowbird is projected to rise about 33% by 2029 — from 0.07 in 2024 to a central estimate of 0.09 (95% range 0.01–0.18). A 5-year backtest shows a typical error of ±61.5%, with 100% 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 →
20250.100.010.18
20260.100.010.18
20270.090.010.18
20280.090.010.18
20290.090.010.18

Where the Bronzed Cowbird Is Detected

BBS routes recording Bronzed Cowbird, sized by most recent count.

Bronzed Cowbird Population Trend by State

Bronzed Cowbird 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-80%197029
Californiainsufficient datan/a2
Floridainsufficient datan/a2
Louisiana-35%199011
Nebraskainsufficient datan/a1
New Mexico-36%19929
Texas-6%196993

Bronzed Cowbird Population Trend by Region

Bird Conservation Regions are the ecological unit for trends.

Bronzed Cowbird 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 →
Shortgrass Prairie+228%200712
Edwards Plateau+7%19789
Oaks and Prairies+177%197110
Mississippi Alluvial Valley-51%20018
Sonoran and Mojave Deserts-88%197013
Sierra Madre Occidental-72%197017
Chihuahuan Desert-52%198329
Tamaulipan Brushlands-20%196927
Gulf Coastal Prairie+131%197116

Bronzed Cowbird Conservation Status

Our route-weighted index shows it up about 5% 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.