Birdhouses 101

May 23, 2010 § Leave a comment

A larger wren house.

Birdhouses attract the species of birds that naturally nest in tree cavities. This includes woodpeckers, nuthatches, chickadees, titmice, house sparrows, American starlings, purple martins (our largest swallow), house wrens, and bluebirds, as well as some species of owls, wood ducks, and American kestrels (also known as “sparrow hawks”) – our only native falcons – small, colorful raptors that can commonly be seen sitting on power lines along highways as you drive by. Look up sometime, and see if you can spot a large, round, buff and gray-blue bird with black stripes on a white face.

Myself, I only have experience with two kinds of birdhouses – bluebird and wren houses for Eastern bluebirds and house wrens respectively (although you can also set out species-appropriate boxes for owls, wood ducks, kestrels, and purple martins (which use multi-nest houses), but all of above have to be placed way high above the ground, and, as such, would be hard for us to maintain).

Because I live on ten acres, wrens vs. bluebirds nest-box competition is not a big issue here, even though wrens are aggressive and will, if they want to, kick out bluebirds (and even house sparrows) out of the occupied houses. But the good thing is that they prefer houses placed in or near trees and close to human dwellings (hence the name), while bluebirds prefer houses placed in the open country with cut lawns or managed pastures as well as fence posts, low trees and other scattered perches from which to hunt (bluebirds normally feed by perching above the ground and surveying the grass underneath them for insects). Luckily for bluebirds, they get a head start on the house occupation, since they get here as early as mid-March, while house wrens don’t return until mid-May.

With their ability to nest in every nook and cranny, house wrens are very common, in town and in the country. Bluebirds, on the other hand, are quite a bit more rare since they really need long expanses of lawns or pastures (so golf courses and farms are good that way) to feed and rear a family. If you live in the middle of town, wren houses are a better bet.

Design: Bluebirds are large birds, larger than sparrows (though not quite as big as robins). That’s why they require larger houses (9-11″ tall), with a 1.5″-in-diameter entrance hole in order to exclude the competing starlings. Do find a proper bluebird box plan before building one, and be sure it incorporates all of the following:

  • a slightly slanted roof, for the rain to run off
  • a series of holes in the sides close to the top, for ventilation.
  • a series of holes in the bottom for drainage. This is really important!!! You don’t want the babies to drown after the first rain.
  • open and close easily – you need to monitor your bluebird box closely to make sure that no house sparrows are making a nest in there (if they do, just remove it and dispose of it, even if it has eggs or babies), and also to clean out the house after the bluebird family has vacated (=after the chicks have fledged), especially at the end of the season.

Here’s the plan we used to build ours.

Placement: Place your bluebird houses on posts (I use fence posts and grape-vine poles, as in the picture above) about 5′ above the ground (which also makes for convenient opening and monitoring), which is what they prefer. If you have room for multiple boxes, place them 100 to 150 yards apart.

Wren houses:

With bluebirds, the female is responsible for the building of the nest, while her partner cheers her with a sweet song from a nearby perch (remember that the purpose of birdsong is communication – specifically, it serves a dual purpose of announcing/defending a territory and attracting a mate). This is not the case with wrens, where the male, and not the female, will build a rough structure for a future nest out of uniform, coarse sticks in as many as eight or nine cavities at once so as to lay claim to the territory. The female will then examine his work in each of the cavities, and, if he’s lucky, choose the best one, which she will then line with softer material and lay her eggs in. Right now a female is building such a nest in a box on my deck, right outside my door. Tiny but sassy brown birds, house wrens are easy to get to nest in your yard because they are so aggressive, and, apart from their beautiful songs, they give a rattle-like alarm call when their nest is approached.

Design: While wrens will happily use bluebird houses, they will also be happy with smaller houses designed specifically for the species, which have the advantage of a very small ( 1 1/8″) entrance hole which will keep out house sparrows. (Wrens will, if they want to, harass and expel house sparrows from cavities, and remove their nests piece by piece). I bought my wren houses at the local agri-center, where they were labeled as such, but you can also build your own. Many designs are available online – just make sure that the roof is slanted, that there are openings in the top for ventilation and in the bottom for drainage, and that the house can be easily opened and closed for cleaning after the chicks have fledged.

Placement: You’ll want to set out not one but several wren houses at once, and hang them at 6′ or higher above the ground. Wrens like to be near thicker vegetation, so attach wren boxes to trees or use hooks to hang them from branches (wrens don’t mind the swaying). You can even place one on your deck or porch – they like to be close to people.

About bird nests: with the exception of the vacated nests in your bird boxes, which need to be cleaned out regularly, it is completely illegal to tamper with or remove bird nests from trees, let alone remove or tamper with baby birds. Tell your children to not touch bird nests and to not shoot any protected birds (see below for the list of the unprotected species). Educate yourself and your children about which birds are which – turn off that TV, get out a bird guide, and head outside. I believe that conservation is our civic duty, and becoming aware of what species of plants and animals are around us and what their needs are is the first and the most important step.

Exceptions: the three unprotected (invasive) species are house sparrows, European starlings, and rock pigeons, which is why it is OK to destroy active house sparrow nests with eggs or chicks in them, especially if you find one inside your bluebird box.

How to know the difference: House-sparrow nests are tall – they fill the box completely, and they look very messy (in which they remind me of my house), with random objects incorporated into the fabric of the nest. For instance, in addition to grass, you will see pieces of the electric-fence wire, feathers, and even pieces of garbage. House-wren nests are built on a foundation of thick, uniform twigs, and are easily recognizable that way. Bluebird nests are very neat and are built exclusively of fine dried grasses and are only about 3″ or so tall (maybe a little higher). If you are not sure, leave the nest be. Keep in mind that other small cavity-nesting birds might appropriate your nest boxes, and, if they do, you have to let them.

About cut lawns: Don’t spray your lawns! Chemicals in the products can harm the birds that feed on the insects living in or near the ground, robins in particular.

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