Birds of a feather don't always nest together

She was the paragon of parenting. Indefatigably dedicated to child-rearing, she worked with selfless devotion to the care of her young.

Hers is the story, however, of hard-working and well-intentioned parents everywhere whose kids don't quite turn out as they had planned.

The story began when the female Eastern Phoebe gathered nesting material in April. Soon there was a comfy, secure nest atop a gutter and under the eves by my garden. The phoebe laid four eggs and dutifully incubated them 'round the clock for two weeks. This hard-working single mom left the nest only to catch some fast food for herself and hurry back to her incubation duties.

Then the big day came. Looking up at the nest, I could see a hungry gaping mouth. An egg had hatched! For the next two weeks, I watched Mom making forays for food -- high protein insects for her hungry young. She tended the chicks 24/7 until the grand moment of fledging arrived.

Fledging is somewhat like graduation day when parents gaze proudly upon their offspring and tearily watch them launch into the big world.

I had front row seats for the momentous event. The first graduate appeared: A wobbly head with teenage hair. I waited for the pomp and circumstance of the other chicks rising to fledge, but I saw none.

Chick number one (and only) stretched and rose higher. It was big. Awfully big. Bigger than its mom. It was -- an imposter! And it had killed its phoebe nest-mates.

In one of nature's twists of fate, Mom Phoebe had been duped. Her nest had been parasitized by a brown-headed cowbird. Holding a duplicitously earned diploma, the cowbird was the only chick to graduate. Ms. Phoebe had been unwittingly become a foster parent, incubating and feeding someone else's offspring at the expense of her own.

The two parenting styles of the cowbird and the phoebe provide a stark contrast. The phoebe's style is pretty straightforward: mate, build a nest, incubate, feed the ravenous nestlings until they fledge. The cowbird, by contrast, has a different m.o. After mating, she looks for a suitable nest -- usually an open cup structure -- made by someone else. She watches and waits, then sneaks in, lays an egg and splits. Once a cowbird egg is laid in another bird's nest, the cowbird's parenting duties have concluded. The incubation and feeding of her young are left to some hapless host. Kind of like dropping the kids off at child care and not picking them up again -- leaving the expense and hassle of child rearing to someone else.

This strategy is called brood parasitism. To be good at this, you've gotta be quick. And you've gotta be sneaky. The female cowbird is both.

"Cowbirds are the stealth bombers of the avian world, dark shapes that whip into another species' nest just before dawn, often while the owner is away," wrote Susan Milius in Science News Online.

In less than a minute, the female cowbird lays an egg for the host to tend and feed. The cowbird then flies off and repeats the process in another nest. And another. And another. These prolific egg-layers can parasitize 30-40 nests in one season. Their propensity to produce eggs daily gives them the nickname "songbird chickens."

And these chickens aren't chicken. They sometimes push a host egg overboard and/or crush and kill the host nestlings.

Sound cruel? In purely ecological terms, the cowbird just does what it does to survive. As brood parasites, cowbirds are no more nefarious than the leaf-munching monarch caterpillar in the field, the hungry hawk in the sky, or the insect-eating phoebe in our garden. After all, our concept of ethics does not figure into natural selection. Survival -- and production of viable offspring -- do.

Consider the evolutionary origins of the cowbird's brood parasitism and how the cowbird earned the unsavory status as the most unloved songbird in North America. Once called buffalo birds, cowbirds are insect- and seed-eaters who followed herds of bison that kicked up insects and dropped seed in their dung across the great North American prairie. The cowbirds' food source was therefore constantly moving, so they had to move too. This nomadic lifestyle left no time for cowbirds to settle down and make a nest, let alone tend to child care. It was "dump and run" -- or in this case fly -- leaving eggs and offspring for someone else to deal with.

Things began to change for the cowbird in the late 19th century.

"When bison were nearly extirpated from the North American landscape and replaced by cattle, sheep and goats, cowbirds adapted and began to associate with livestock," explained Lisa Petit in her article "Brown-headed Cowbirds: From Buffalo Birds to Modern Scourge."

Life got a bit easier for the cowbird. The spread of agriculture and eventually suburbia over the former prairie meant fragmented habitat and lots of good pickings in terms of food and host nests.

"In the last century, Brown-headed Cowbirds have experienced massive range expansions and population explosions," wrote Petit. "Shadowing their livestock-associates, cowbirds occur in regions where bison did not previously exist and forage in the grain crops, feed lots and grain silos often found nearby livestock."

The impact of cowbirds on songbird populations varies locally and from species to species. Some studies show that cowbirds are not as devastating to songbird populations as once believed - habitat loss is the main culprit in the decline of bird species.

But where cowbirds are a problem, they are a problem because we have made them so. They love suburbia, where we have fragmented the landscape with gardens, parks, and forest preserves. They flock to our bird feeders stocked store-bought seed, and they dig the wonderful habitat we've created for phoebes, warblers, vireos and other bird species that traditionally nest on the edge of woodlands.

What can be done to protect native songbirds from cowbirds? It is illegal to kill adults, young or eggs -- cowbirds, too, are protected as native migratory birds.

"The most effective way to control cowbird numbers," wrote Petit, "is to control the features of the environment on which they thrive. Landscape-level measures that maintain large forest tracts with minimal edge to interior ratios ... would be most effective."

The Forest Preserve District of Kane County's natural areas management plan includes large-scale restoration. Large preserves with contiguous natural areas are less appealing to cowbirds and hence more beneficial to would-be host songbirds. Preserving and restoring large tracts of land benefits countless other species as well, both plant and animal.

It's a wild kingdom out there. Watch the bird feeders in your garden and you may witness the dynamics of bird ecology right before your very eyes.

To help native birds and their habitats, check out the many opportunities to volunteer in habitat restoration. See the District's website at http://www.kaneforest.com/volunteer/workdays.aspx. You may also check out the year-round activities of Kane County Audubon at http://www.kanecountyaudubon.org/.

&bull Valerie Blaine keeps an eye on nests and nestlings, predators and prey and other wild happenings in Kane County. A naturalist for the Forest Preserve District of Kane County, she welcomes your wild questions about the wild kingdom of Kane County. You may reach her at blainevalerie@kaneforest.com.