Until fairly recently, bluebirds were uncommon in Connecticut. From 1900-1970, bluebird populations decreased 90%, mainly due to loss of habitat (open space and snags), and competition for nesting sites from non-native starlings and house [English] sparrows). However, bluebirds are coming back. They are fascinating, beautiful birds. You can help increase their numbers. Here’s how.
Learn to Recognize Nests and Eggs. Eastern bluebirds build neat, cup shaped, woven nests of 100% fine grass or pine needles, and occasionally bits of fur. Eggs are powder blue, or sometimes white. House sparrow nests are a tall jumble of odds and ends, including coarse grass, cloth and trash, feathers, twigs. Eggs are usually cream with irregular brown speckles. See Sialis.org for information on other common nestbox inhabitants, such as the iridescent, brave, mosquito-munching Tree Swallow.
Put up Nesting Boxes. In Connecticut, bluebirds start checking out nesting sites in February to mid-March. Build or purchase a nesting box designed specifically for bluebirds. These boxes are made of unpainted 3/4" - 1" wood; have an overhanging slanted roof, no perch, a round 1.5" diameter hole, ventilation, and drainage holes; are deep enough so predators can't reach in and get to the eggs; and have a door that opens for cleaning and monitoring. Mount boxes on 8 ft., 3/4" diameter galvanized pipe, with the entrance hole at least 5 ft. off the ground. The best locations are semi-open grassland, like mowed meadows, large lawns, cemeteries, orchards, roadsides, and areas with scattered trees and short ground cover.
Control Predators and House Sparrows. Install predator buards to keep raccoons etc. from raiding nests (e.g., a 2 ft. long, 8" diameter stovepipe or PVC pipe sleeve on the pole, mounted under the box).
DON'T hesitate to destroy house sparrow nests and eggs. House sparrows, which some bluebirders refer to as “rats with wings,” are introduced invasive pests, and are not protected by law. You might think they're cute, but they will attack and kill adult bluebirds (sometimes trapping them in the nest box), and destroy eggs and young. House sparrow nests, eggs, young, and adults may be legally removed or destroyed. It is better to have no box at all than to allow house sparrows to reproduce in one.
Supplement Food and Water. Bluebirds don’t eat bird seed. Plant native trees, shrubs or vines that provide fall and winter food for bluebirds, such as flowering dogwood, holly, mulberry, wild grape, and Virginia creeper. Consider offering mealworms. Birdbaths should be no more than 3" deep, with gently sloping sides, and a rough surface. Remember to change the water every few days to keep it fresh.
Don’t get discouraged if you don’t get bluebirds nesting the first year – it’s worth the wait!