When is the best time to set out nesting boxes? To maximize your chances of attracting bluebirds, very early spring is your best bet. Here in Massachusetts, I like to have them up by early March. This will give most bluebirds a chance to claim boxes before the tree swallows arrive.
Actually, anytime is a good time to put up nesting boxes. Bluebirds will generally have more than one brood, so they may still be loooking for nesting sites in early and mid-summer. Recently I've noticed a number of bluebirds choosing to remain here during the winter months. Although nesting boxes are a poor substitute for roosting boxes (birds at the bottom of the pile may suffocate), they will provide protection from the harsh winter weather.
I've always been at odds on deciding if I should take down nesting boxes or leave them up for the winter. I generally take most of them down for the winter for a new coat of linseed oil and leave at least one at each location, should the birds need them. In some cases the houses were used by bluebirds and some were taken over by mice. I even had a flying squirrel take up residence in one. I continue this practice (mostly for the mice & squirrels) but now add a roosting box for the birds. This larger box has an entrance hole at the bottom, with staggered 1/4" dowels for birds to perch on in the upper area. There have been recorded instances of up to 14 eastern bluebirds squeezing themselves into a regular nesting box to avoid cold winter nights. Unfortunately, this sometimes results in the soffocation of some of the birds at the bottom of the box.
Note: I will add a more detailed section on roosting boxes in the future.
Whether you build your own or purchase, the next question is; where should you place them to best attract bluebirds? It's been my experience that bluebirds are more easily attracted to large open areas such as pastures and hay fields, especially if there is a fence line. They seem especially fond of hunting insects from the vantage point of a fencepost or wire. This is not to say they won't be attracted to a nesting box in a residential area, but between food requirements and the probable harrassment from house sparrows, you will most likely optimize your chances in large open areas. Most farms or people owning large tracts of open land will welcome the addition of bluebird houses (I've made many new friends this way) as long as you ask permission.
Placement of the houses can be anywhere from 4 to 10 feet off the ground. For monitoring and cleaning convenience, mount them so they can be easily inspected without having to stand on something (eye level). Also try to mount boxes so the entrance hole faces a small tree or bush, which will allow the young a safe landing place on their initial flight. You may also consider facing the entrance hole away from north or prevailing winds and harsh afternoon sunlight.
MOUNTING TIP: If wooden fence posts are available, these would be most convenient for attaching nesting boxes to. I mount mine by drilling two 1/8" holes vertically in the back of the house. Then attach to fence posts using 2" speed screws (drywall or deck screws). Many houses can be easily mounted this way using a cordless drill. Sometimes, if fenceposts are short, I will place the house on top of the post and use a 2" X 18" piece of wood, securing this to the back of the house and the fencepost. If you experience or anticipate problems with raccoons , houses can be mounted on electrical conduit or galvanized pipe, that the coons cannot readily climb (they can also be greased for snakes). These are available at most hardware stores, are inexpensive, and can simply be pounded into the ground anywhere you like. For a more secure mount, you can first drive a 5' section of rebar (inexpensive rod for reinforcing concrete) 2.5' to 3' into the ground, then sliding electical conduit over this rod.
Another question for house placement is; how far apart should the houses be mounted? I've varied this distance considerably over the years with no consistent conclusion. Some people mount boxes in pairs to minimize competition, so bluebirds and tree swallows, for example, can share the same territory without bickering over a single nesting site. This sometimes works, but I've had aggressive male bluebirds (an exception to the rule) that not only defended their own house but would not allow any other birds to nest in another house 30 feet away. If you're just starting out with a bluebird trail, try mounting houses 50 to 80 feet apart and see what happens. You can always add a box or two if you see too many squabbles.
What is a bluebird trail? Almost any amount of nesting boxes mounted in a given area can be called a bluebird trail. A trail can consist of just a couple of boxes or hundreds of them, depending on your interest and preferences. Generally (if more than a couple) they are mounted in a line or along a fenceline where you will travel this "trail" many time through the course of the nesting season, checking activity. You could even set them out in a circlular fashion to enable you to start and end your walk where you park your vehicle.
OK, what is monitoring, anyway? In birding circles, people who maintain nest box trails generally like to keep records of any activity along the trail. As an example, if you know the date when the eggs in a certain house were laid, you will then have an idea of when to expect them to hatch and also when the nestlings will likely fledge (leave the nest). After some experience and by keeping track of nest building activity, you will eventually be able to tell what kind of birds are using a house by the material found in the box when the birds are not seen in the area. Keep a log by date and simply write down anything new that is found each time you visit. You may want to keep track of the type of material and when the nest was completed, date and number of eggs laid, when and how many hatch and the date and number of young that actually leave the nest.
How often should a trail be monitored? Plan to monitor your bluebird trail as often as you can. Usually a weekly visit is enough to gather information on when nests are built, eggs are laid/hatched and dates when young leave the nest. Not only will the birds need your assistance at times, but if you take some time to just observe the birds along your trail, you will be rewarded with endless hours of entertainment. With that discovery, you will probably find yourself visiting more frequently.
Now let's go to page 3 to see what we can expect during the nesting season.