My adventures in the woods, streams, rivers, fields, and lakes of Michigan

Brown-headed Cowbird, Molothrus ater

Note: this post, while published, is a work in progress, as are all posts in this series, My Photo Life List. My goal is to photograph every species of bird that is seen on a regular basis here in Michigan, working from a list compiled by the Michigan chapter of the Audubon Society. This will be a lifelong project, that I began in January of 2013, and as I shoot better photos of this, or any other species, I will update the post for that species with better photos when I can. While this series is not intended to be a field guide per se, my minimum standard for the photos in this series is that one has to be able to make a positive identification of the species in my photos. The information posted here is from either my observations or the Wikipedia, the online free encyclopedia, however, I have personally shot all the photos appearing in this series.

Brown-headed Cowbird, Molothrus ater

This is another species that I thought that I would never post about. Since they are parasitic nesters, I was taught to shoot them on sight as a young boy.

They occur in open or semi-open country and often travel in flocks, sometimes mixed with Red-winged Blackbirds (particularly in spring) and Bobolinks (particularly in fall), as well as Common Grackle or European Starlings. These birds forage on the ground, often following grazing animals such as horses and cows to catch insects stirred up by the larger animals. They mainly eat seeds and insects.

Before European settlement, the Brown-headed Cowbird followed bison herds across the prairies. Their parasitic nesting behavior complemented this nomadic lifestyle. Their numbers expanded with the clearing of forested areas and the introduction of new grazing animals by settlers across North America. Brown-headed Cowbirds are now commonly seen at suburban bird feeders.

This bird is a brood parasite: it lays its eggs in the nests of other small passerines (perching birds), particularly those that build cup-like nests. The Brown-headed Cowbird eggs have been documented in nests of at least 220 host species, including hummingbirds and raptors. The young cowbird is fed by the host parents at the expense of their own young. Brown-headed Cowbird females can lay 36 eggs in a season. More than 140 different species of birds are known to have raised young cowbirds.

Some species, such as the House Finch feed their young a vegetarian diet. This is unsuitable for young Brown-headed Cowbirds, meaning almost none survive to fledge.

The acceptance of a cowbird egg and rearing of a cowbird can be costly to a host species. In the American Redstart, nests parasitized by cowbirds were found to have a higher rate of predation, likely due in part to the loud begging calls by the cowbird nestling, but also partly explained by the fact that nests likely to be parasitized are also more likely to be predated.

Host birds sometimes notice the cowbird egg, to which different host species react in different ways. Rejection manifests in three forms: nest desertion (e.g., Blue-gray Gnatcatcher), burying of the egg under nest material (e.g., Yellow Warbler), and physical ejection of the egg from the nest (e.g., Brown Thrasher). Brown-headed cowbird nestlings are also sometimes expelled from the nest. The Gray catbird rejects cowbird eggs over 95% of the time.

It seems that Brown-headed Cowbirds periodically check on their eggs and young after they have deposited them. Removal of the parasitic egg may trigger a retaliatory reaction termed “mafia behavior”. According to a study by the Florida Museum of Natural History published in 1983, the cowbird returned to ransack the nests of a range of host species 56% of the time when their egg was removed. In addition, the cowbird also destroyed nests in a type of “farming behavior” to force the hosts to build new ones. The cowbirds then laid their eggs in the new nests 85% of the time.

On to my photos:

Male Brown-headed Cowbird

Male Brown-headed Cowbird

Female Brown-headed Cowbird

Female Brown-headed Cowbird

Female Brown-headed Cowbird

Female Brown-headed Cowbird

Female Brown-headed Cowbird

Female Brown-headed Cowbird

Male Brown-headed Cowbird

Male Brown-headed Cowbird

This is number 74 in my photo life list, only 276 to go!

That’s it for this one, thanks for stopping by!



6 responses

  1. Well, aren’t they the nasty little buggers? I haven’t noticed them around here, but then I haven’t exactly been looking for them either.

    April 2, 2013 at 2:22 am

    • I don’t know if they live that far to the west. And yes, they are nasty little buggers!

      April 2, 2013 at 2:49 am

      • Hoping they don’t spread out to here then.

        April 2, 2013 at 3:20 pm

  2. Echoing the sentiments of Gunta there…these are bully-birds! You know I never fully appreciated the different colours that birds have till I started following your blog QSP. Excellent work! 🙂

    April 3, 2013 at 9:41 am

    • Thank you! Hopefully with spring coming, I’ll get some of the really colorful birds when they arrive.

      April 3, 2013 at 9:46 am

  3. I actually think these guys are rather cute. Wonderful captures Jerry, I’ll send some to you as they’ve been here with me for a while.

    April 3, 2013 at 5:56 pm