In the wild, bluebirds forage small insects and fruit, so they are not often seen visiting traditional feeders that offer seed. They can, however, learn to eat from a feeder, and they will quickly learn to use one in order to spend their energies on caring for their young instead of foraging for food. Their feeder favorites are mealworms and small pieces of fruit or berries, including raisins. When insects and other natural food supplies are scarce, they will also eat small peanut and sunflower kernels, as well as suet. Bluebird feeder types range from dish-style to the predator-resistant, house-style.
Mealworms are available live, roasted or canned. Live mealworms are obviously the closest match to a bluebird's native diet, while roasted mealworms have a longer shelf life and do not require refrigeration. Canned mealworms are processed in a way that locks in their nutrients and juices. If you choose to offer fruit, you can cut fresh fruits, or offer a number of varieties of dried fruit such as blueberries, cranberries, raisins and cherries. Some owners use a seed blend with fruit in hopes of attracting bluebirds to feed at their traditional feeders.
The population decline of eastern bluebirds in the early 20th century was due to loss of habitat and competition for nesting sites from the aggressive house sparrow, a European species introduced to North America in the mid 1800s. This decline encouraged an interest in offering bluebird houses to help increase their populations. Since bluebirds compete with house sparrows and European starlings for nesting spots, there are a couple of things you'll need to keep in mind in order to offer a nest box that will deter these competitors. First of all, the nest box should be constructed of wood with 1-1/2" entrance hole and no perch. This opening size should exclude starlings. House sparrows, however, will still be able to access through a 1-1/2" entrance hole. To deter them, you will need to restrict the internal dimensions. Most pundits would agree that a nest box with cozy 4" x 4" inside floor dimensions is adequate for eastern bluebirds (5" x 5" for mountain and western bluebirds), while effectively deterring house sparrows. Bluebird nest box heights generally range from 8-12" high. Consider a Bird Guardian Birdhouse Predator Protector to prevent predatory mammals and birds from reaching into the birdhouse and destroying the nest and occupants. Make sure the house has drain holes. Clean the box at the beginning of the season and preferably after babies fledge to encourage multiple broods.
Place your bluebird house 5 to 6 feet off the ground. Ideally, it should be located on open land, not in a wooded area, although a few nearby trees are okay. Some landlords believe the nest box should be located within 50 feet of a tree, with door facing the tree, so fledglings will have a place to fly to and perch after their first flight attempts. This will help them avoid falling to the ground and becoming prey to predators. Another thing you need to know about attracting bluebirds to nest is that there is a difference between nest spacing and nest pairing. Bluebirds are competitive with each other, so they require nest spacing of at least 100 yards from each other. However, bluebirds have been known to nest adjacent to swallows, so you can pair nest boxes 10-25 feet apart to allow a bluebird family and a swallow family to live in close proximity of each other.
Other Ways to Attract Bluebirds
Birds need a source of fresh water for drinking and bathing. Add a birdbath to your landscape so they'll have a spot to splash about, clean their feathers, and drink water. They prefer running water to standing water, so many people add a dripper to their birdbaths.
You will also want to plant native species that produce berries bluebirds eat. Bluebirds are known to consume the fruits of plants such as flowering dogwood, eastern red cedar, holly, American elderberry, and pokeweed. These plants will also attract other species that are interesting to watch, so they are well worth the effort.