I am discouraged at the number of House Sparrows I see nesting in bird boxes in my neighborhood. Some of our neighbors have allowed us to put hole restrictors on their boxes to keep the House Sparrows out and allow smaller birds like House Wrens and chickadees in. People enjoy attracting birds to their yards and the idea of providing a place for them to raise their young is especially appealing, but they have no idea that putting up a decorative box is creating a House Sparrow factory, which, from an ecological standpoint, does more harm than good.
If you really want a decorative box, make sure it remains a decoration and block the entrance hole. If you want to host cavity-nesting birds, you should be a good landlord! Ergo, this Bootstrap Public Service Announcement #1: Tips for Backyard Nest Boxes.
- Make sure the entrance hole is sized precisely for the species you want to attract (and remember, there are a limited number of species that will use nest boxes). For House Wrens it should be no larger than one inch in diameter (any hole 1.25″ or larger will admit House Sparrows). Even better: an entrance slit (one inch tall and up to four inches long).
- Make sure the box is placed in the appropriate habitat for your target species.
- Make sure the entrance hole is positioned the correct distance from the bottom of the box so that nestlings are able to leave the nest.
- Mount the box on a pole to prevent predators access. Poles may have to be greased or fitted with a baffle to discourage climbing predators such as snakes, cats, or raccoons. Place the box high enough so that cats can’t jump on the box.
- Nest boxes must be maintained. Old nests must be cleaned out of the box after the young have left the nest. This gets rid of parasites, discourages the boxes from being taken over by wasps, spiders or mice, and eliminates a build-up of nest material that would hinder new nesting attempts.
- Immediately remove nest materials if House Sparrows begin building in your box. You may have to do this several days in a row. If they persist, take the box down or move it. Since House Sparrows are not native to North America, they are not a protected species, and it is okay to remove their eggs or nestlings from a box.