Bluebird Boxes

Nesting session is here! Get your Bluebird boxes ready

By Krista White

The Eastern Bluebird male has a bright blue back and head, a white body, and a reddish-brown chest. The female mimics the male’s colors but are more subdued with a grayish body. Eastern Bluebirds are found from the eastern side of Montana, down through Mexico, and up through the eastern portion of the U.S. and Canada. Not only revered for its beautiful coloring and song – it is also the International Symbol of Happiness for many locations throughout the world.

Bird of the Week: Eastern Bluebird – Huron-Clinton Metroparks
Photo credit: Huron-Clinton Metroparks

Once threatened with extinction during a mass species population decline in the 1920s-1970s, the Bluebird population has made a rebound, but it is still at risk.

“If we don’t help them, they will cease to exist,” said Kim Springer, a lifelong birdwatcher, Buhl Park Wildlife Committee member, and creator of the Buhl Park Bluebird Trail.

The Bluebird’s natural habitat, which consists of making nests in existing tree cavities, is slowly being wiped out due to human population expansion and encroachment by two non-native bird species: House Sparrows and European Starlings.

House Sparrows and European Starlings (introduced into the U.S. in the 1800s) are prolific breeders and aggressive, said Springer. They take up most natural tree cavities that Bluebirds require to flourish.

Bluebirds are a boon to the environment. They are proficient bug eaters with a diet consisting of 70-90 percent insects and invertebrates, she said. Unfortunately, this is also one of the issues threatening them – eating bugs that have ingested chemicals, such as pesticides and herbicides.

Anyone can put up a Bluebird box, and just one box can help the population, said Springer. Before you do, read Springer’s Bluebird box tips and tricks below.

Location. Bluebirds like meadows, lawns, grassy fields, low-growth, and scattered trees. Golf courses are one of the best Bluebird box locations, but make sure that there is some sort of cover nearby, she said. Bluebirds like to have young fledge from the box and need to get to a nearby bush or tree. Don’t put your box too close to the woods because you will attract predators and other bird species, Springer warns. Also, if you are placing your box(es) on a farm, make sure you keep them away from grain silos and areas where you feed your animals. You’re more likely to get a House Sparrow nest vs. a Bluebird one at those locations, she said. If placing multiple boxes, Springer suggests putting them 300 ft apart. The box should face north, east, or somewhere in-between those two. Ensure that there is a fresh water source, such as a birdbath, located near the box.

Box design. There is no perfect box design and none that are House Sparrow proof, but there are Bluebird boxes standards to follow when building a box. Normal box size includes a 4×4 inch floor, a depth of (minimum) six inches, and an entrance size of one inch in diameter if round or 1 1/8 inch if using a slot shape, said Springer. The best wood for the box includes rough-cut cypress, redwood, pine, or cedar (non-aromatic). Don’t use pressure-treated lumber, and don’t paint the inside of the box. You can paint the outside of the box, if desired, just make sure to use light, neutral colors, she said. Dark colors can overheat the babies. The box should also include 1/4-inch vent holes on each side and have drainage holes in the bottom. A plexiglass window maybe also be installed, and some experts think it helps deter House Sparrow nesting. Include a “door” that allows you to access the box for cleaning and monitoring purposes.

Predator deterrent. Never hang a Bluebird box from a tree, said Springer. Mount your box on a post, such as a piece of electrical conduit. Grease the post after installation so that nothing can climb up to the nest. Also, consider installing a predator guard on the post, such as a baffle, a piece of heating duct, or even a bucket to ensure predators can’t access the box. If House Sparrows or European Starlings move into a box, you can remove them. But, if you keep getting them in your boxes after removal, your yard might not be the place for a Bluebird box, she said.

Timeline. Put up boxes in late winter/early spring. Bluebird nesting season is February-October. The females lay an average of 4-6 eggs, which are powder blue; although, up to five percent of Bluebird eggs are white. It takes an average of 11-20 days to brood, and when fledglings are 13-21 days old, they begin to take flight. At five weeks, they are flying on their own. The female can have up to three broods/year, so there is a chance that multiple broods are living in the box at the same time, helping to take care of the new fledglings. 

Monitoring. If you plan to put up a Bluebird box, you must commit to monitoring it, she said. Check your boxes once a week to ensure there are no cracks, that they are staying dry and clean, to watch for wasps, to ensure the right species is nesting, and to check for predators and invasive insects, such as blowflies. Blowflies deposit larva into nests, which suck the blood of the Bluebird babies. If you end up with a blowfly invasion, Springer suggests forming a low-profile box (about an inch in height) with hardware screen/mesh, or the bottom of a plastic strawberry basket, and placing the nest on top of the constructed box. This causes the blowfly larva to fall to the bottom of the box instead of staying in the nest. Don’t check the boxes in the early morning, if the temperature is under 50 degrees, or in the evening. It’s best to check the boxes in the warmer afternoon, she said. If the fledglings jump out of the box while you are checking it (and it’s too early for them to be fledging), Springer said to pick them up and put them back in the box, covering it opening with your hand for a few moments. And don’t worry about the mom. Springer said it’s an old wives’ tale that the mother won’t attend the birds if touched.

Cleaning. If you come across a broken egg or a dead nestling while checking your box, Springer suggests removing it. Remove any broken eggs with a spoon, so you don’t risk breaking the other eggs. Makes sure to dispose of any broken eggs or dead nestlings far away from the box, so you aren’t attracting predators, she said. At the end of the season, Springer suggests cleaning boxes out. Bluebirds may nest year-round, but if the box is not in use in the off-season, she said to take it down or leave the door open.

Time to ready bluebird nesting boxes | News, Sports, Jobs - The Express
Photo credit: Pennsylvania Game Commission

**Interested in helping monitor the Bluebird Trail at Buhl Park? Kim Springer is hosting two Bluebird informational seminars at the activities building in Buhl Park on March 16 at 10:00 a.m. and 6:30 p.m. Registration is required, and participants are asked to pick one session to attend. To register, email Katie Nowland at or call 724-981-5522, ext. 105.

For more information about Bluebirds, check out these sites.