BirdAnalyst
Species · BBS 2025 Release · 1966–2024

Brown-headed Cowbird

IcteridaeGeneralistsMolothrus ater

Brown-headed Cowbird has edged down: down 11% on the route-weighted index since 1968.

-11%Since 1968TrendPercent 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 →
4,121RoutesSurvey routesHow many standard-protocol BBS routes contributed counts. More routes means a steadier, better-sampled index; very thin coverage is suppressed.Full methodology →
58Years 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 Brown-headed Cowbird

A brood parasite that lays its eggs in other birds' nests, the Brown-headed Cowbird followed the great bison herds and now feeds in farmland and pasture across the continent.

Size
6.5–8.5 in long, about 1.6 oz (16–22 cm, 44 g)
Habitat
A broad range of open and wooded habitats, often near people.
Diet
Seeds and grain, with insects in the breeding season.
Range
Recorded on 4,121 Breeding Bird Survey routes across 49 states, most concentrated in the Appalachian Mountains.
Family
Icteridae · Generalists
Conservation
Least Concern

Notable Brown-headed 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 Brown-headed Cowbird. See the full index history below.

Brown-headed Cowbird Population Forecast

If the recent trend holds, Brown-headed Cowbird is projected to stay roughly flat through 2029, near 11 (95% range 9.1–12). A 5-year backtest shows a typical error of ±2.7%, with 100% 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 →
11Projected 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 →
9.1–1295% 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 →
±2.7%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, Brown-headed Cowbird is projected to stay roughly flat through 2029, near 11 (95% range 9.1–12). A 5-year backtest shows a typical error of ±2.7%, with 100% of held-out values landing inside the 95% band.19662029
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 →
2025119.312
2026119.212
2027119.212
2028119.112
2029119.112

Where the Brown-headed Cowbird Is Detected

BBS routes recording Brown-headed Cowbird, sized by most recent count.

Brown-headed Cowbird Population Trend by State

Brown-headed 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 →
Alabama+6%1968108
Alaskainsufficient datan/a2
Arizona-56%197088
Arkansas-14%196962
California+35%1970245
Colorado+391%1970158
Connecticut-33%196820
Delaware+374%196817
Florida+207%1968104
Georgia+238%1968110
Idaho-24%197064
Illinois+155%1968105
Indiana+8%196869
Iowa+85%196939
Kansas-11%196967
Kentucky-38%196864
Louisiana+30%1969100
Maine-81%196868
Maryland+37%196876
Massachusetts+30%196832
Michigan-62%1968108
Minnesota+71%196990
Mississippi+56%196874
Missouri+25%196994
Montana+251%1970116
Nebraska+25%196976
Nevada+176%197048
New Hampshire-62%196825
New Jersey+168%196843
New Mexico-7%197084
New York-42%1968128
North Carolina+188%1968108
North Dakota+82%196951
Ohio-2%196889
Oklahoma-57%196971
Oregon-48%1970138
Pennsylvania-38%1968137
Rhode Island+174%19687
South Carolina+565%196850
South Dakota+32%196965
Tennessee+22%196854
Texas-61%1969246
Utah+39%1970108
Vermont-77%196826
Virginia-23%196888
Washington-52%1970108
West Virginia-68%196863
Wisconsin-43%196898
Wyoming+388%1971130

Brown-headed Cowbird Population Trend by Region

Bird Conservation Regions are the ecological unit for trends.

Brown-headed 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 →
Northern Pacific Rainforest-76%1970112
Great Basin+19%1970256
Northern Rockies+42%1970220
Prairie Potholes+45%1969124
Boreal Hardwood Transition-77%1968125
Lower Great Lakes / St. Lawrence Plain-37%196886
Atlantic Northern Forest-80%1968144
Sierra Nevada-30%197039
Southern Rockies / Colorado Plateau+49%1970234
Badlands and Prairies+82%1969138
Shortgrass Prairie+29%1969136
Central Mixed Grass Prairie-13%1969130
Edwards Plateau-47%196920
Oaks and Prairies-61%196974
Eastern Tallgrass Prairie+72%1968277
Prairie Hardwood Transition-24%1968161
Central Hardwoods+3%1968166
West Gulf Coastal Plain / Ouachitas-54%1969110
Mississippi Alluvial Valley+42%196873
Southeastern Coastal Plain+134%1968343
Appalachian Mountains-46%1968400
Piedmont+7%1968170
New England / Mid-Atlantic Coast+54%1968164
Peninsular Florida+525%198059
Coastal California+49%1970116
Sonoran and Mojave Deserts-37%197076
Sierra Madre Occidental-66%197035
Chihuahuan Desert-66%196956
Tamaulipan Brushlands-51%196928
Gulf Coastal Prairie+4%196948

Brown-headed Cowbird Conservation Status

Least Concern

The IUCN Red List rates this species as Least Concern. Our route-weighted index shows it down about 11% since 1968.

Source: USGS North American Breeding Bird Survey, retrieved 2026-05-22. Trend is a route-weighted relative-abundance index, not an absolute population.