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Brown-headed Cowbird, John Reynolds
Photo © John Reynolds

Photo: John Reynolds
Breeding evidence - Brown-headed Cowbird
Breeding evidence
Probability of observation - Brown-headed Cowbird
Probability of observation
Elevation plot - Brown-headed Cowbird
Elevation plot

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Brown-headed Cowbird
Molothrus ater
Landscape associations:

Click on plot to view table of mean abundance
Elevation range:
0 - 1930 m
Conserv. status:
Not at risk
Global importance
of B.C. population:
6
Number of squares
ConfirmedProbablePossiblePoint counts
241 359 617 554
Long-term BBS trends
RegionYearsTrend (conf. interv.) Reliab.
Brit. Col.1970 - 2012 -3.37 (-4.35 - -2.24)Medium
Canada1970 - 2012 -1.57 (-2.12 - -1.08)High

Mean abundance by region

Bird Conservation Regions [plot]
NW Interior ForestBoreal Taiga PlainsGreat BasinNorthern RockiesN. Pacific Rainforest
0.070.24 0.160.19 0.2
Ecoprovinces [plot]
N. Boreal Mountains Taiga Plains Boreal Plains Georgia Depression Sub-Boreal Interior
0.070.05 0.260.2 0.12
S. Interior Mountains Central Interior Southern Interior S. Alaska Mountains Coast & Mountains
0.210.16 0.17  0.21

Mean abundance by habitat [plot]

Boreal Altai Fescue AlpineBoreal White and Black SpruceBunchgrassCoastal Douglas-fir
 0.240.120.25
Coastal Mountain-heather AlpineCoastal Western HemlockEngelmann Spruce -- Subalpine FirInterior Cedar -- Hemlock
 0.160.070.21
Interior Douglas-firInterior Mountain-heather AlpineMontane SpruceMountain Hemlock
0.19 0.3 
Ponderosa PineSpruce -- Willow -- BirchSub-Boreal Pine -- SpruceSub-Boreal Spruce
0.160.070.120.13

Characteristics and Range The Brown-headed Cowbird is North America's best-known obligate brood parasite, meaning that it does not build its own nest but instead lays its eggs in other species' nests. It has been recorded parasitizing over 200 bird species, with at least 80 species targeted in British Columbia, including more than 20 that are commonly parasitized (Campbell et al. 2001). Formerly concentrated in the central part of the continent where it followed American Bison (Bison bison) herds and was called the "buffalo bird", Brown-headed Cowbird populations exploded across North America with the clearing of forests. With these population expansions cowbirds were implicated in the decline of many songbirds (Lowther 1993). Its range now spans most of North America from the southern Boreal Forest south to central Mexico; northern breeding populations are short to medium-distance migrants.

Distribution, Abundance, and Habitat In British Columbia, the Brown-headed Cowbird is widespread in southern coastal, southern interior, central and northeastern regions. A major provincial range expansion occurred over the past century, but the Atlas distribution appears much as that depicted in The Birds of British Columbia published in 2001, except for a slightly increased area of occupancy in the northeast.

The Probability of Observation model and abundance based on Atlas point counts match the distribution closely, showing the main centres of abundance to be the Peace River lowlands in the Boreal Plains, the Georgia Depression, and secondarily the valleys and plateaus of the Southern Interior, Central Interior and Southern Interior Mountains ecoprovinces. Campbell et al. (2001) considered the highest breeding season numbers to be in the Southern Interior and Southern Interior Mountains; Atlas results suggest that whilst the range expansion may be slowing, the centre of highest abundance may be shifting.

It is a common bird of natural grasslands and human-modified habitats especially agricultural land and fragmented forest, occurring in a wide variety of drier biogeoclimatic zones, preferring lower elevations, and reaching peak abundance between 250 and 500 m, but it will breed as high as 2,000 m.

Conservation and Recommendations Brown-headed Cowbird populations across much of North America have declined significantly over the last 40 years (McGowan and Corwin 2008, Cadman et al. 2007), including in British Columbia, although the core population in the Prairies remains stable (Environment Canada 2014). Declines may be related to blackbird control programs and increased forest cover in some parts of the continent. Concern that increasing Brown-headed Cowbird populations were a leading cause of declines in passerine bird abundance has been re-evaluated: for most species the declines were probably the result of habitat loss and fragmentation, with Brown-headed Cowbird brood parasitism as a secondary factor (Smith et al. 2000, Jewell and Arcese 2008). Restoration of habitat, rather than aggressively controlling Brown-headed Cowbird populations, has been suggested as a better way to manage for at-risk passerine species parasitized by cowbirds.

Brian Starzomski

Recommended citation: Starzomski, B. 2015. Brown-headed Cowbird in Davidson, P.J.A., R.J. Cannings, A.R. Couturier, D. Lepage, and C.M. Di Corrado (eds.). The Atlas of the Breeding Birds of British Columbia, 2008-2012. Bird Studies Canada. Delta, B.C. http://www.birdatlas.bc.ca/accounts/speciesaccount.jsp?sp=BHCO&lang=en [10 Dec 2018]

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