Words On Birds by Steve Grinley
Time to Prepare Nest Boxes for Bluebirds
March 07, 2020
by Steve Grinley
Bluebirds are already scouting for nest boxes. A few early tree swallows have been spotted in Massachusetts and they, too, will soon be searching for residences. It is, therefore, time again to provide my 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 late March or early April. Swallows will follow, in search of nest sites soon after they arrive in the weeks ahead. 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.
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. Other popular styles include the Peterson box, which is wedge-shaped with a sloping, overhanging roof that helps deter predators, and the Kentucky style, with a long entrance slot at the top, said to deter house sparrows. A house made of PVC is also thought to discourage sparrows.
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. Further distance from trees may be necessary if house wrens are present. In an open field, a tall stick in the ground near the house can be a favorite perch for bluebirds while they forage for food or guard the house. 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 seven 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 often compete for the same house as bluebirds. Swallows are also beautiful birds. They eat flying insects, so they are beneficial 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 competitor. 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 to encourage them to stay. Once the bluebirds begin nesting, you can continue to help them by providing mealworms in a nearby feeder. This will minimize the time the male spends away from the nesting box, where 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.
Boxes should be cleaned after bluebird 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 the past few 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 control insects in our yards and gardens.