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The House Wren: The Unjustly Accused

In the early 1900s, when  began noticing House Wrens nesting in her backyard in Iowa, she was delighted. Opportunistic nesters, House Wrens will set up shop in pretty much any empty crevice they can find—John James ���Ϲ���’s illustration of a House Wren family depicts them nesting in an old hat—and over the next several years, as Sherman hung birdhouses in her yard, more wren tenants eagerly filled the vacancies. At one point, there were 10 pairs nesting on the property, each raising at least five chicks a season. All the while, Sherman, an artist and budding ornithologist, meticulously recorded the birds' rendezvous, their squabbles, their romances, and their parenting trials.

But before long, Sherman’s admiration for the wrens began to sour. First she saw one invade a Phoebe nest and toss out two eggs—an “evil deed,” in her journal. Then, when two wren-beak-sized holes appeared in the shell of a Black-billed Cuckoo egg, she described the bird as a “frightful devil that thrust its sharp bayonet into the egg.” In time she came to launch a full-fledged crusade against the House Wren, publishing her observations—and condemnations—of the bird in scientific journals, and demanding that ornithologists and bird-lovers face the facts, denounce House Wren boxes, and end their fawning over these “criminal” birds.

At the time, some ornithologists wrote Sherman off as overly emotional—to which she countered that they were the emotional ones, too attached to their little brown birds to see them for the monsters they really are. "They are fond of their bird and are angry when the truth is spoken about it," . "They act precisely like the parents of vicious children, refusing to believe the evil things their darlings do."

And indeed, over the last century, have confirmed Sherman’s observations: Wrens will puncture the eggs of bluebirds, woodpeckers, nuthatches, sparrows, chickadees, swallows, Bobolinks, and warblers, and occasionally take over their nests. It would seem that the House Wren is, as Sherman put it, a “felon, criminal, demon, and devil.”

Or is it?

You could say the House Wren was doomed to get caught up in the sticky code of human morality from the start. In a strange twist of etymological fate, Troglodytes aedon, which translates roughly as “crevice-dwelling nightingale,” was named after a child-killer—Aëdon, the Queen of Thebes, who in Greek mythology accidentally killed her own child while aiming for the son of a rival, and was then transformed by Zeus into a nightingale. And in the human world, as in the world of the Greek gods, infanticide is generally frowned upon.

But the wrens don’t kill for vengeance; they do it for survival. Competition is fierce among cavity-nesting birds, especially for those like the House Wren that can’t carve out a home for itself. It must discover an existing hole to nest within—and if there isn’t a vacant spot available, it does what it must to survive and reproduce.

We’d prefer that the bird patiently and politely wait its turn, perhaps. But evolution rarely rewards patience. Indeed, House Wrens are fiercely impatient across the board. In many cases, a male House Wren may lure a second mate to move in to a nest site on his territory while his primary mate is still incubating their clutch. Or he may sneak out to woo the female on a neighboring male's territory—perhaps destroying her eggs or young afterwards so that she must lay new eggs (his eggs) in their place. And if a male holds no territory he may boldly attempt to take one by force. The usurper sometimes succeeds in driving out the resident male, claiming his mate, and killing her eggs or young so that she must start over. The fiercest males are the most successful—and pass on those fierce genes to their abundant offspring. 

Why House Wrens go after the eggs and young of other species (especially those who don’t nest in cavities) is difficult to explain. It might reduce competition for food, suggest some researchers. But perhaps there’s simply no downside to destroying any and all unrelated eggs—for the wrens, anyway.

It doesn’t look pretty. But who are we to judge? As the prominent ornithologist Witmer Stone—who, as it happened, agreed with Sherman that reducing the number of House Wren nest boxes in certain areas would be wise—: “The Wren is no more of a ‘felon’ for destroying the nest of a Bluebird than is a Flicker for destroying a nest of ants.”

Sherman, though, remained unpersuaded. She even went as far as to write her backyard wrens out of her will, stipulating that the birds be barred from breeding on her homestead even after her she was gone. But in spite of her crusade, the species is today one of North America’s most common songbirds—helped along, no doubt, by the same opportunism that Sherman considered so morally wrong. Ecologically speaking, at least, the House Wren seems to be doing something right.