Our Actions Have Amplified Cowbird's Impact

At the end of February, the when the red-winged blackbirds migrate North, their raucous noise is replaced by the gurgling murmur of a handful of brown-headed cowbirds. My feelings towards cowbirds are mixed because they are fascinating native birds who are part of nature just doing what they do, even though what makes them interesting is one of nature’s peculiarities that has been amplified by our actions.

Cowbirds are different in a significant way from 99% of other birds species. .

Cowbirds are masters of observation about other bird’s nesting habits and able to exist because they can modify their own environment to maximize their own survival. Cowbirds are considered obligate brood parasites, meaning they never build their own nests but lay their eggs in the nest of over 220 different species. They have evolved to cleverly remove and replace other bird’s eggs with their own. Some birds like robins will notice, but many won’t.

When robins find a cowbird egg in their nest they throw it out. Most bird species take care of the egg.

With so much energy spent on reproduction, not on rearing their young, during nesting season cowbirds are able to lay about 40 eggs in dozens of nests - about 10 times more eggs than other birds. To increase survival, their eggs hatch a day earlier than the host eggs and the chicks are physically bigger, more aggressive about begging for food as well as faster to grow and fledge.

All cowbirds are raised by other bird species. Before ever meeting other cowbirds, this brown-headed cowbird fledgling will innately know how to sing like a cowbird and in time will seek and mate with another cowbird.

The cowbird's name is believed to come from the way they followed bison and cattle (cows!) in search of insects either on their back or that they unearthed with their hooves. This unusual behavior worked when there were plenty of bison and open prairies, but since the American landscape changed, cowbirds have adapted and been able to expand their range and multiply. Like the grey squirrels that once migrated across our vast forests, cowbirds have evolved to live in more urbanized areas where they now contribute to the decline in some songbird species. The fragmentation of our forests leaves many bird species who once lived in forest interiors vulnerable to cowbirds who prefer nests at the edge of the forest.

Female cowbirds monitor the nesting behavior of other birds. Today this one is sharing a feeder with a chipping sparrow, this spring she may parasitize its nest.

Every year when I see a brown cowbird fledgling being taken care of by an attentive foster mother bird, I worry about how cowbirds might be affecting the fragile ecosystem in my part of the world where developers rule, and I can see the songbird’s habitat disappearing in real time. Atlanta is still clinging to the nickname the City in The Forest even though our once famous tree canopy is spiraling downwards towards the critical 40% threshold. Below this number we will join other cities around the country that have become what is known as an urban heat island. Our tree canopy is vital habitat for songbirds and the sparser it gets, the easier it is for cowbirds to thrive.

Every year my yard is filed with funny, awkward cardinals like this cutie. So far, I haven't seen too many cowbirds among them, but I see a handful of cowbirds around nesting season each year.

Like most of the wildlife challenges we’re facing, the diminishing songbird problem is not because of one bird species, but about us needing to change our behavior and offer a richer habitat for songbirds where cowbird behavior would again become a quirk of nature and not contributing to an already dire situation like it is now.

Cowbirds are not the enemy, they have merely adapted in fascinating ways to a fragmented habitat we have irrevocably created and continue to diminish.

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