I have a nest box in my backyard, right near the woods, where I get Carolina chickadees nesting most springs. Our property is too wooded for bluebirds, but we really enjoy watching the chickadees raise a brood each year.
This year a friend gave us a small wren house, which we hung up in our apple tree next to our garage. Within days, the wren house was full of small sticks and the male wren was singing his heart out from the top of the box.
The next thing we know, the chickadee nest is empty and the six eggs are pierced and lying on the ground below the box. The chickadee parents are nowhere to be found. The only other clue was a couple of small sticks on top of the chickadee nest, just like the ones in the wren nest box. Could our house wren have destroyed the chickadee eggs? Do birds do that? And if so, what can we do to prevent it in the future?
—Chickadee Fan, Nashville, Tennessee
Dear Chickadee Fan,
I believe you may have solved your own backyard murder mystery. Despite their small size, sweet voice, and mouse-like appearance, house wrens are indeed very territorial during the nesting season. Male house wrens typically build several stick nests inside suitable cavities within their territories. The females (which return later in the spring than males) then visit these prospective nest sites and select one for nesting. If other birds try to nest in cavities within a male house wren's perceived "turf", he may destroy the eggs by piercing them and/or throwing them out of the cavity. This may seem unnecessarily violent, but it is the house wren's way of keeping his nest-site options open. So, he stays busy building partial nests and singing his loud, rolling burble of a song, hoping to attract a passing female house wren on his tour of homes.
Once a female chooses him and one of his nests sites, they work to finish the nest. Once she begins laying eggs, his penchant for egg destroying ceases abruptly. But does the male house wren stick around to help his mate raise the brood? Nope. He heads off into the underbrush looking for other females to mate with—just another strategy to get his genes out there in the world in the form of offspring.
One of the best strategies for dealing with marauding house wrens is to place your nest boxes out in the middle of an open area. Many cavity-nesting birds will still use a nest box in such a setting, but house wrens rarely do. They prefer to be in the woods or on the edge of the woods. Bluebirds, swallows, flycatchers, chickadees, and titmice will all use a house placed in an open setting.
One final bit of advice: If you find a house wren's nest already going, don't remove it or hinder it in any way. First of all, it's not legal to destroy the nest of a native songbird. But more importantly, house wrens, being the competitive little so-and-sos that they are, have been known to go on a rampage if their nest is destroyed. They will destroy the eggs of whatever cavity-nesting neighbors they can find and have even been seen destroying or damaging the eggs of cup-nesting birds such as sparrows and robins.
If you've got a pair of nesting house wrens, let them do their thing until the season is over, then remove the housing opportunity if you don't want them coming back.
I've got to say, in all my years of living in the woods, I love to hear a house wren singing, but I've never actually met one that I liked.