Brown-headed Cowbirds

By Terry Grabill
Photo by Rachel Bosma Kramer
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One joy of being a member or administrator of birding groups on social media is the many images captured by experienced, talented photographers.  I particularly like the discussions brought on by newer members working to identify birds that are new to them.  It makes me happy when more experienced birders help a new guy through the key points of identifying this “new” species.  Then…then comes a picture of a smallish black bird with a rich, brown head…the brown-headed cowbird.  Seldom have I seen a discussion become heated like those regarding brown-headed cowbirds.  

Cowbirds are migratory birds, related to red-winged blackbirds and grackles.  They prefer open areas of fields and pastures to forests and marshes.  Like many songbirds, the male is more striking in coloration than that drab gray of the female.  Cowbirds are also nest parasites.  Female cowbirds do not make nests or care for their young.  Nesting for cowbirds involves spying on another bird, following it to its nest, waiting until the appropriate opportunity, and then laying an egg in its nest.  If things go well for the cowbird parents, the “host” female will incubate the nest and raise the cowbird baby to fledging, when it will begin its life as a cowbird.  A real wonder of nature is how it even knows it’s a cowbird and that it should seek out other cowbirds!

It’s this reproductive strategy that raises the ire of many.  Humans have the unrealistic expectation that animals in nature exhibit similar values and emotions to ours.  By human standards, cowbirds are deadbeat parents.  They seem lazy and take advantage of others’ efforts, and we often feel they should take care of their own families and pull their weight in parenting.  This tendency to assign human thoughts and values to non-human animals is called anthropomorphism, and we’re very good at it!  If we saw our fellow humans behaving as such, we would be appalled and likely have good company in our opinion.  

So, why in the world do brown-headed cowbirds do this?  And, are they causing any harm to the hosts that they parasitize?   To understand this behavior, we must go back in time.  Cowbirds adapted to following the vast herds of bison over the North American prairies, feasting on the insects flushed by the roaming beasts.  Unlike birds, bison, being mammals, carried their embryos along with them and their pause to give birth was short.  Perhaps, in response to the need to move with the herds, cowbirds that were most successful deposited an egg in this nest…and an egg in that nest, leaving the host birds to tend to their babies.  The behavior was carried with the species as its range expanded with the opening of the Great Lakes region to farming.  So, why don’t they do the proper thing now that they don’t have to follow bison?  Again, we assign human values and emotions to non-human animals…it just doesn’t work that way!

Native Great Lakes songbirds seem to do just fine with this parasitism. In spite of the stress on the individual mothers, most species suffer no ill-effect.  An exception has been the Kirtland’s warbler, which nests in a VERY restricted area of north-central Michigan.  The warblers have been critically endangered, and cowbirds were compounding the endangerment.  In warbler habitat, cowbirds were trapped out to ensure the warbler nests were holding only warbler eggs.  This practice has since ceased as the warbler’s populations increased. 
 
Adding to their “distasteful” behavior is the act of terror sometimes brought down on hosts that reject the cowbird eggs.  It’s sometimes called “mafia” behavior.  The cowbird parents monitor the host nest and if their egg comes up missing, the cowbirds may destroy the host nest.  It’s a bit reminiscent of an episode of “The Sopranos”! 

Important to remember as we consider this marvel of natural adaptation is that, being migratory songbirds, they have complete protection of our federal government under the migratory bird treaty.  Their eggs must not be disturbed under penalty of law.  While we tend to want to “save” our favorite birds from these bullies, in order to really appreciate nature, we need to let nature take its course.  
Happy Birding! 
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For BirdGoober, I’m Terry Grabill

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