Daniel Burden
Program Specialist, Value Added Agriculture
Iowa State University Extension & Outreach
Wrens are one of the neatest birds to have on your acreage, and especially around your garden. In Iowa we have several resident and migrant species of wrens hat include house, Carolina, winter, sedge, marsh, and the occasional rare sighting of Beewick’s, rock, cactus or canyon wren. Most wrens are secretive little creatures that live in the forest or marsh, but one is very familiar to people and their gardens, the house wren Troglodytes aedon. Appropriately named (Troglodytes means “cave dweller”), these little guys are cavity nesters who readily take to nest boxes, and not just boxes, house wrens will move into almost any enclosure that has adequate internal dimensions and will remain relatively cool in the warm summer sun.
Wrens are voracious insectivores, insect and spider predators that make wrens great to have around the garden; rather than catching prey on the wing like swallows, fly catchers or warblers, house wrens like to poke around, investigating under and between leaves and loose bark, and climbing around through vines, wood and brush piles. As a child I learned early on that these all-natural “biological-control” agents were incredibly effective against almost all insect pests of the vegetable garden. Just hang a nest box close to the garden and let them do their thing.
Although tiny creatures, house wrens are incredibly vocal, active and are aggressively territorial. This trait prohibits placing nest boxes too close to one another, or within a sight line. If one nest sight can see another, there will be problems. Usually several hundred yards of separation is necessary to keep the pairs happy in their own territories.
As a boy I cut my teeth on elementary woodworking by repurposing old boards into bluebird, tree swallow and wren houses. At some point, my father created a wren house out of a metal coffee can. To our surprise, the wrens preferred it to any of the commercial plastic houses that we had purchased or traditional tried and true wood houses that we built from plans. Over the years, I’ve had a lot of fun knocking out batches of coffee-can houses and giving them to friends for their yards and gardens. These houses are extremely tough and last for years. Once a house starts to rust or look a little shabby, I grab a can of tan or olive-drab camo duck-boat paint at the end of the season and spray on a fresh coat of visual appeal. In the shadowy limbs of the pine tree in my backyard, the house pretty much disappears. If you are putting them out in the timber on your acreage and don’t mind a big colored coffee can hanging in at tree, there is no need to paint them until they need to be refurbished.
The can hangs horizontally from a tree limb with the door opening in the upper part of the lid. To make a house, one needs to punch or drill two ¼-ing holes in one side of the can for a clothing-hanger wire or cord hanger in what will be the top of the house, and a few holes in the opposite side for ventilation and drainage. I also put a few holes in each end for additional ventilation.
The plastic lid needs a bit of reinforcement. From scrap ¼-inch plywood or paneling, I cut a disc a bit smaller than the lid and attach it to the inside of the plastic lid using a few long staples that I then peen-over or “clinch” into the plywood. For years I’d then cut the door hole by chucking a 1-1/8-inch hole saw into my drill press and cutting a hole through the plastic and plywood toward the top of what will be the top of the lid. The size of the entrance hole is critical, if it is even 1/8-inch too large, the house will be immediately occupied and defended by the introduced house sparrow formerly known as the “English” sparrow. These are the all-too common non-native sparrows that are gluttons for birdseed at feeders and are well documented killers of native songbird nestlings.
I have found that house sparrows love these houses as much as the house wrens and will chew at the door opening to enlarge it. This is easily remedied by purchasing and attaching a sparrow excluder, most are powder-coated (hard-painted) metal discs with the proper door size for wrens and tree swallows. The excluder is attached on the outside of the house to protect the hole with two small wood screws provided with the disc. They are inexpensive and are readily available on-line or at bird shops and many lawn and garden stores.
The houses should be cleaned out at the end of the season; wrens like a clean cavity to stuff in the spring. It’s always fun to examine the architecture of the nest structure inside the can. The birds break off tiny dry twigs, usually from pines, and create an interwoven mass that fills at least three quarters of the cavity. In the rear of the house near the back wall there is a little cup-like depression lined with down and the found small feathers of other birds. This is where the birds spend the evening and the female wren will lay her one or two tiny eggs and care for the nestlings.
A final note, if you are going to build a coffee-can wren house, might as well build five or six. It really does not take much time to knock them out. They will be much appreciated by fellow gardeners and make great educational gifts for children.