About fifty species of cavity-nesting birds will use birdhouses, thirty-five of them do so on a regular basis. Man-made nesting boxes provide important cavities for many of these species, because natural cavities in snags (dead trees) and large live trees are, more and more, in short supply in city and suburban yards. The birds don't find much in the way of housing in these areas, so if you provide artificial holes for them and give some attention to detail, you'll be able to attract the wild birds you want and exclude those that are less desirable. If you provide a place for them to nest, you'll have the pleasure of seeing them frequently at close range. Also, birds that use nesting boxes tend to be prodigious eaters of insects, which is an added reason for attracting them with birdhouses.
Choose the site for putting up a birdhouse carefully. Nesting boxes for forest species like chickadees and woodpeckers must be mounted directly on trees. Otherwise, those hung in or fastened to trees should be clear of the main trunk and placed where sunshine can reach them. It's a good idea to position new birdhouses in the autumn before the leaves fall so you can be sure the spots won't be too dark and gloomy. Baby birds, like all growing things, need sunshine.
Nesting time will vary with the bird species, as well as your geographical location. For same year occupancy, nesting boxes should be in place no later than January in the southern tier of states, February for the middle tier and March in the northern states and Canada. If birds seem to be ignoring the houses you've installed, be patient. Sometimes a brand new house is viewed with suspicion, and the birds will be more likely to accept it once it has weathered a bit – another reason why fall is a great time for putting up new houses.
It's easy to provide features that will make the nesting boxes more attractive as residences. Birds might spook if they fly to an entrance hole and find the inside of the box pitch black, so choose boxes with ventilation holes near the top of the sides (or drill your own) to provide some light as well as fresh air. Wood chips and shavings on the bottom of the box will be gladly accepted, and for chickadees and small woodpeckers you can completely fill the box with shavings and let the bird make its own cavity. Don't use sawdust as it doesn't ventilate and dry out as well as chips. Offer nesting materials where the birds can find them without trouble if you really want to make them happy!
Make sure you can get to the box easily, as it should be cleaned out each fall when the nesting season is over to cut down on parasites like mites and lice, and discourage mice from nesting there. Clean between broods as well if your birds are the kind that raise more than one family per season.
Pick a quiet area and avoid having the entrance to the nesting box face a busy road. Make sure to place it near trees and shrubs so fledglings can hide and avoid being eaten by the neighborhood cat while developing their flying skills. In southern regions, it makes sense to have the entrance face north to avoid heat buildup in the box; in northern regions, having the entrance face south might help to keep it warm.
Four to five houses per acre is about right as you don't want to create a bird slum.
Predators, such as cats, squirrels, raccoons, rats and snakes, will always be a problem, so in most areas complete protection is probably not possible. However, there are several things you can do to help keep the nest safe:
- Perches aren't needed on a nesting box and will only serve to attract house sparrows and starlings.
- Mount a cone-shaped metal guard beneath the birdhouse if it's mounted on a pole; if the nesting box is mounted on a post that cats or squirrels can climb, wrap the post with sheet metal.
- Be precise with the entrance hole size necessary for the birds you wish to attract.
Attach a block of wood 1 inch thick with a hole the same size as the entrance hole over the front of the box, creating a short tunnel which will help prevent squirrels or raccoons from reaching into the nest. Make sure to sand the hole in the block so it is smooth.
Of course, it's hard to predict what birds will like when it comes to their nesting boxes, but it is generally assumed that most birds prefer a natural-look, so use brown, tan or grey stain or paint for the exterior finish. On the other hand, some studies have indicated that wrens prefer red or green houses. The interiors of nesting boxes should always be left unfinished.