Time to Ready Nest Boxes for Bluebirds
March 04, 2022
by Steve Grinley

     Snow remains on the ground and spring is still more than a couple of weeks away but bluebirds have already been seen scouting for nest boxes. It is, therefore, time again to provide my annual refresher on attracting bluebirds and swallows:

     Now is the time to put up a nest boxes or clean out existing ones, as bluebirds will begin nesting by mid to late March. Bluebirds are experiencing a housing market similar to our own with high demand and low inventory. So having a nest box selected, up early, and ready for them will increase your chances of having bluebirds nest in your yard.

     For the best chance to attract bluebirds you’ll want a nesting box designed for them. Though there are many different styles, most have a 1½ inch opening that is about six or seven inches above a four-inch square floor. Some have predator guards over the hole to help deter squirrels, raccoons and larger birds. Metal plates around the hole help prevent squirrels from chewing and enlarging the hole.

     If you plan to monitor the house during the nesting season, you should have one that is easy to open with minimal disturbance to the nest. Bluebirds like an open area for feeding, so placement of bluebird houses should be in or near grassy areas. It is best to place the house on a separate pole away from the tree line, preferably with a baffle on the pole. Direct placement onto a fence post or tree can also be successful, but more difficult to discourage predators.

     The house should be placed between four and six feet high, facing away from foul weather winds. Like many birds, bluebirds are territorial, that is, they will not allow another pair of bluebirds to nest too close. If you are putting up multiple houses, they should be spaced about 100-300 feet apart.

     Tree swallows, which arrive later in March, often compete for the same house as bluebirds. Swallows are also beautiful birds and eat flying insects, so they are beneficial birds as well. For that reason, many people place pairs of houses within 10-25 feet of each other to allow bluebirds and tree swallows to nest side by side. In this way, both species’ presence helps control both crawling and flying insects.

     These two species also help protect each other from the aggressive house sparrow, their number one enemy. House sparrows often take over bluebird nesting boxes and will even kill adult bluebirds or swallows in the process. Because house sparrows are so aggressive, bluebird houses should be placed as far away from buildings as possible and they should be monitored on a regular basis, especially early in the nesting cycle. If sparrows are present, their nesting material should be removed. If sparrows become a real problem, trapping and removing the sparrows may be necessary.

     Once bluebirds arrive, you can put out mealworms and/or bluebird “nuggets” (suet) to encourage them to stay. This will minimize the time the male spends away from the nesting box, so that he can protect his mate from intruders. The female does most of the incubating and only leaves the nest periodically to feed. Thus, having mealworms nearby will help shorten her absence from the nest and further increase their chances for a successful brood.

     Bluebirds have two, and sometimes three broods in a season, so if they don’t move in right away, you may still attract them later in May and June. Boxes should be cleaned after fledglings leave the nest as the adults may use the same house for another brood. Houses should also be cleaned after every nesting season and checked again just before spring. They often use the nest boxes for winter roosting if they stay in the area during colder months. Once established, bluebirds will return to the same area every year and more boxes can be added for returning offspring.

     These beautiful birds have made a comeback in recent decades due to efforts of homeowners providing suitable nesting habitats for them. In turn, the bluebirds provide us with their beautiful colors and song, and they help naturally control insects in our yards!