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Eastern Bluebirds

Until fairly recently, Eastern Bluebirds (Sialia sialis) were uncommon in Connecticut, mainly due to loss of habitat open space/snags), and competition for nesting sites from introduced species (starlings and house [English] sparrows). However, bluebirds are coming back.  They are fascinating, beautiful birds.  You can help increase their numbers. The keys are:

Bluebird nest. Photo by Bet ZimmermanTree swallow nest. Photo from http://www.wbu.com/chipperwoods/photos/treeswallow.htmChickadee nest. Photo by B ZimmermanTufted titmouse nest. Photo by Bet ZimmermanHouse wren nest.  Photo by B Zimmerman

Learn to recognize nests and eggs (more photos) - also see chart on relative sizes of eggs.

  • Bluebird: Neat, cup shaped, woven nest of 100% fine grass or pine needles. Occasionally bits of fur or a few feathers and rootlets. Fairly deep nest cup. Eggs are powder blue, sometimes white. NOTE: Western Bluebirds will routinely add ribbons, cellophane, feathers, thin bark and leaves to their nest.
  • House Sparrow: Jumble of odds and ends, including coarse grass with seedheads, cloth, white feathers, twigs and sometimes litter. Tall nest, may have tunnel-like entrance. Eggs are cream, white, gray or greenish, with irregular brown speckles.
  • Tree Swallow: Nest of grass lined with feathers. May be messy. Flatter cup than bluebirds. Eggs are pure white.
  • Black-capped Chickadee: Downy nest of moss, fur, and soft plant fibers. Female may cover eggs with moss when leaving the box.  White eggs with brown speckles.
  • Tufted Titmouse: Downy nest of moss, fur, and soft plant fibers. May have many earwigs living in it. White eggs with rose/mauve speckles.
  • House Wren: Messy nest of twigs, occasionally lined with fine fibers or feathers. Males may build unlined eggless "dummy nests" in nearby boxes to reduce competition. Tiny glossy white eggs, sometimes tinted with pink/buff, with lots of fine pinkish brown/reddish brown/brown specks that sometimes form a ring on the larger end of the egg.



bullet Build or purchase a nesting box designed specifically for bluebirds. These boxes are made of PVC or unpainted, untreated 3/4" - 1" wood, have an overhanging slanted roof (2-5", with a shallow saw kerf (groove) to keep rain from soaking into box), no perch, a round 1.5" diameter hole (or 1.375" x 2.250" oval hole. Mountain Bluebirds need a 1 9/16" hole), ventilation, drainage holes, deep enough so predators can't reach in and get to the eggs, and a door that opens for cleaning and monitoring (if rough wood is not used, add kerfs to inside of door to enable fledglings to climb out). Birds may roost in the boxes in cold weather, and the ground may be frozen in February/March when they start house hunting, so put boxes up in late fall or winter. See plans.
bullet Put up nest boxes in semi-open grassland habitat, such as mowed meadows, large lawns, cemeteries, orchards, roadsides, and areas with scattered trees and short ground cover. Areas with fence lines, some medium size trees, or telephone lines provide perches for hunting and nest-guarding. If no native birds use the box for two years, try a different spot.
bullet Mount boxes on 8 ft., 3/4" diameter galvanized pipe, with the entrance hole 5 ft. off the ground. If away from prevailing winds, face E/N or NE.
bullet Keep boxes 125-150 yards apart. If nesting bluebirds are harassed by Tree Swallows, or more than 50% of bluebird trail boxes are occupied by swallows, set up a second, "paired" box 5-20 ft. from the first. Boxes that Tree Swallows nest in should have "kerfs" or grooves (saw marks about 3/4" apart) or 1.5-2" wide x 6" long plastic screen (gutter guard) stapled tightly inside below the entrance hole to enable fledglings to exit.
bullet Install predator guards to keep snakes, raccoons and other predators from raiding nests (e.g., a 2-4 ft. long, 8" diameter stovepipe or PVC pipe sleeve on the pole, mounted (so it wobbles) just under the box), even if you don't have problems the first year of nesting. Losses without predator protection may run 25-33%.
bullet If squirrels chew the entrance hole to widen it, screw a metal hole guard (available from birding stores like Wild Bird Crossing) or a 1.5" thick block of hardwood with a 1.5" entrance hole over the damaged hole, or replace the front part of the box.
bullet Try attaching strands of 10 lb. fishing line to boxes and feeders to scare House Sparrows. Sparrow spookers made of mylar are also effective.
bullet Plant native trees, shrubs, and vines that provide fall and winter food for bluebirds. Consider offering mealworms.
bullet Provide water.
bullet Monitor boxes at least once a week to check on progress and control House Sparrows, blowflies, etc.
bullet Remove eggs that have not hatched 5 days after last egg hatched.
bullet Bluebirds like a clean box. Remove bluebird nests as soon as the young fledge, or if nesting fails, to encourage another brood. Put nests in the trash to avoid attracting predators. If mice nest in the boxes over the winter, clean them out in February.
bullet Replace or repair any split, rotten, or broken pieces on boxes that could let rain in and chill nestlings. 
bullet Be patient! See more tips. And be prepared to become possessed by these captivating birds.
bullet DON'T install nestboxes in brushy and heavily wooded areas, too close to trees or shrubbery.
bullet DON'T install nestboxes within 200 yards of barnyards where animals are fed, or where House Sparrows are abundant unless you are willing to actively manage House Sparrow populations.

bullet DON'T mount boxes on trees or fence lines--they provide easy access for predators. Other birds species are more likely to use boxes on trees.
bullet DON'T install boxes near where pesticides or herbicides are used. Don't use pesticides inside boxes.
bullet DON'T hesitate to destroy House Sparrow nests and eggsHouse Sparrows are non-native invasive pests, and are not protected by law. You might think they're cute (some bluebirders refer to them as "rats with wings"), 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 humanely destroyed under federal law. It is better to have no box at all than to allow House Sparrows to reproduce in one.

bullet DON'T remove Tree Swallow, Tufted Titmouse, wren, or chickadee nests. It is illegal to disturb a nest with eggs of any bird except House Sparrows, starlings and pigeons, which are not protected. Empty House Wren nests can be removed.
bullet DON'T feed corn, bread, milo, or millet in bird feeders, as this attracts House Sparrows.  Stick with black sunflower seed, thistle (nyjer/niger/nyger) and fruit. Or try a Magic Halo.
bullet DON'T worry that monitoring will make the parents desert the nest. Bluebirds tolerate human presence. Touching the nest will not make the birds leave--your mother just told you that to keep you from harassing them. Most birds don't have a good sense of smell.
bullet DON'T monitor more often than 2x/week, or in early morning (as eggs are usually laid 1-2 hours after sunrise)/evening/during bad weather.
bullet DON'T touch eggs while monitoring. Some, especially chickadee eggs, are very fragile. Also oil from hands could inhibit hatching.
bullet DON'T open the boxes once the birds are 12-14 days old. (Their eyes are fully open when they are 8-11 days old. Parents may just dip their heads into the box hole to feed the young at this age). It can cause young to fall or hop out of the nest box before they are capable of flying, reducing their chances for survival.
bullet DON'T paint boxes, especially with a dark color. If desired to preserve wood, coat exterior only with linseed oil or a product like SUPERDECK (Coastal Gray), and allow to dry thoroughly before box will be used.
bullet DON'T assume the nest is abandoned.  During egg laying, adults may spend very little time in the box.  On hot days, the female may leave the nest for long periods of time. The only sure way to know the nest is abandoned is if neither parent has visited the nest for four full hours after the young have hatched. If it has been abandoned, contact a licensed wildlife rehabilitator (or the North American Bluebird Society for advice.).
bullet DON'T get discouraged if bluebirds don't nest in your boxes the first year.

Bluebird Timetable in Connecticut - see photos of nestling development

bullet Scouting: February to Mid-March: Bluebirds start checking out nesting sites. Late arrivals, or previously unpaired birds may nest as late as July or even August, and some pairs have multiple broods. It's never too late to put up a nestbox, as they may be used for a subsequent nesting (see Number of Broods), for roosting, and are also often checked out in the fall by birds that may return the following spring.
bullet Nest building: 2-6 days.
bullet Egg laying: 5-7 days. Usually laying one per day, for a total of 4-7 eggs. Often start egg laying a few days after nest is completed. Egg laying can be delayed (sometimes for a week or two - 3 weeks is not unheard of) in cold weather, for young parents, or in cases where food is scarce.
In Connecticut, the first egg is generally laid in April. (Earliest reported in CT: First week of March. Latest reported in August - 3 broods that year.  One brood/year is more common in CT.)
bullet Incubation: 12-14 days. Doesn't start until all eggs are laid. They may wait about a week if weather is still cold.
bullet Fledging: 16-21 days, typically 17-18. Occasionally a runt will fledge one or even two days later than the others. When they are first born, they look "a bit like hairy shrimp." Insect availability may speed up or delay fledging. Once they leave the nest, bluebirds do not return to it. When the babies are 28 days old, they can fly well. They can feed themselves by Day 30.
bullet Number of Broods: One to four broods per year. Fourth brood attempts may be made in southern climates. The number of broods probably depends on timing, temperatures, food availability, box availability and the experience or age of the parents. A subsequent brood may be started within days or weeks of fledging the previous brood. It may be in the same box or a different box.

If you keep track of dates, you will be able to avoid opening the box after the young are 13 days old, to prevent premature fledging.  At this age, bright blue feathers are evident on males. Also see www.texasbluebirdsociety.org "Eastern Bluebird Nestling Daily Growth Series" to help determine age. Bluebirds may raise 2-3 broods in one season. Some studies have shown that 30% of bluebirds return to previous nesting sites the following season. If you would like to join the participants in Connecticut's Bluebird Nest Box Network, contact Geoff Krukar at (860) 675-8130.

Four day old bluebirds.  Photo by Bet Zimmerman.Food

68% of a bluebirds' diet is made up of insects: grasshoppers, crickets, beetles, spiders, and caterpillars. They also like fruit - e.g., flowering dogwood, holly, mulberry, wild grape, Virginia creeper, pokeweed, and Viburnum. (Although they will eat the fruit of multiflora rose and Japanese honeysuckle, these are invasive species, and should be eradicated.)  Bluebirds love mealworms. They may eat suet (see link for recipes). Bluebirds rarely eat birdseed (they will occasionally take sunflower chips).

More Information:


  • Most of the information on this page is from Sialis.org, a bluebird conservation and education resource.
  • Berger, Kridler and Griggs, The Bluebird Monitor's Guide, 2001.
  • State of Connecticut, Department of Environmental Protection, Eastern Bluebird, Wildlife in Connecticut, Informational Series, 1997.
  • State of Connecticut, Connecticut Wildlife, Bluebird Bulletin , March/April 2002.
  • Stokes, Donald and Lillian, Bluebird Book: The Complete Guide to Attracting Bluebirds, Boston, 1991.
  • Zickefoose, Julie, Enjoying Bluebirds More, The Bluebird Landlord's Handbook, Birdwatcher's Digest Press, Marietta, Ohio, 1993.
Conservation Commission
The bluebird carries the sky on his back

- Henry David Thoreau