The Eastern Bluebird

Over the years land has been cleared for housing and industrial developments, shopping malls, highways and cropland. Many old trees have been cut down for firewood and wooden fence posts that once provided nesting cavities have now been replaced with metal posts. With modernization, the supply of natural nesting cavities for Bluebirds and other native cavity-nesters has been greatly reduced.

Compounding the problem of habitat loss has been the introduction into North America of two imported species – the House Sparrow and the European Starling. Both species are cavity-nesters and both are very aggressive. House Sparrows are small enough to enter any hole that a Bluebird can and are so aggressive that they will damage eggs, kill young and even kill adult Bluebirds that are trapped inside a nestbox. Starlings can be excluded from Bluebird boxes by using the correct size entrance hole but will out-compete Bluebirds for woodpecker holes and other natural nesting cavities.

During the summer, Bluebirds feed mainly on insects. In the winter, Bluebirds depend on many kinds of wild berries for their food supply. However, the supply of wild berries has also decreased over the years. The few berries that remain are often stripped quickly by large flocks of starlings.

Even though the Bluebird population has greatly decreased, the future can still be promising for them. The most important step we can take to help bring back the Bluebirds is to provide nesting sites by setting out a Bluebird box or starting a Bluebird trail. A Bluebird trail is a series of Bluebird boxes placed along a prescribed route. In areas where nesting boxes have been put up in suitable habitat, Bluebird populations are increasing. Bluebirding is a great environmental, hands-on project that people of all ages can enjoy. By following the instructions below, chances are good that you will be able to attract and enjoy Bluebirds.

The Bluebird Nestbox
A good Bluebird nestbox should be well ventilated, watertight, have drainage holes, be easy to monitor, and easy to clean. Cedar and redwood are ideal although plywood and other types of wood can be used. Boxes can be painted or stained if a light color is used.

• Treated lumber should not be used because of its toxic content.
• A Bluebird box should never have a perch. Sparrows and wrens are attracted to perches.
• Boxes for Eastern Bluebirds should have a round entrance hole of 1 1/2″. Mountain Bluebirds need an entrance hole of 1 9/16″; Western Bluebirds will use a 1 1/2″ hole, but a 1 9/16″ hole should be used where the Western & Mountain Bluebird ranges overlap.

Mounting the Nestbox
MBS recommends that nestboxes be mounted on free-standing smooth round pipe — 3/4″ electrical conduit works well, but any round pipe will also work. Nestboxes should be mounted at a height of about 5’ for easy monitoring and a predator baffle, such as the Kingston stovepipe baffle, is recommended to deter raccoons, snakes and other climbing predators. Coating the pole (under the baffle) with grease can also keep ants from reaching the nest. Avoid mounting Bluebird nestboxes on fences or trees as this makes the nesting vulnerable to climbing predators such as snakes and raccoons. If possible, mount boxes so that the entrance hole faces away from prevailing winds.

Habitat
Habitat is a key factor to consider when setting up a Bluebird trail. Open, rural country with scattered trees and low or sparse groundcover is best. Suitable habitat should include perch sites, such as a fence line, wires, or tree branches where Bluebirds may perch to search for food. Look for these when you are selecting a location for your nestboxes. If Bluebirds do not like the habitat, they will not use your boxes.

• Pastureland, acreages, parks away from human traffic, and mowed areas such as cemeteries, golf courses are all good locations for a Bluebird trail (provided pesticides are not used).
• Avoid brushy and heavily wooded areas — this is the habitat of the House Wren. Avoid areas where the House Sparrow is abundant (i.e. farmsteads and feedlots).
• Avoid areas of heavy pesticide use.
• Mount nesting boxes so the entrance hole is approximately five feet above the ground. If possible, face the box away from prevailing winds and facing towards a tree or shrub which is within 100 feet of the box. Trees and shrubs provide a landing spot for the young Bluebirds when they fledge. This will keep them off the ground, away from predators.
• Boxes for the Eastern Bluebird should be spaced at least 100 to 150 yards apart; Western and Mountain Bluebirds have a larger nesting territory and boxes should be spaced no closer than 300 yards apart.
• Boxes can be mounted in pairs in areas where Tree Swallows are abundant. When paired, boxes should be mounted 5 to 25 feet apart. This provides nesting sites for both species and helps to prevent competition between them. Different species of birds usually do not mind nesting close to each other.
• Bluebirds rarely nest in cities. It is possible, but uncommon, for Bluebirds to nest along the outer edges of cities or in small towns. Bluebirds generally prefer rural areas.

Monitoring a Bluebird Trail

• Do not put up a Bluebird box if you do not plan to monitor it. Check your Bluebird boxes at least once a week during the nesting season, until chicks are close to fledging.
• Do not open the box after nestlings are 12 to 14 days old. Doing so could result in the nestlings leaving the box before they are able to fly, greatly reducing their chances of survival.
• Always remove House Sparrow nests immediately. Never allow House Sparrows to nest in your nestboxes!
• Nestboxes should be in place by February or March so that the Bluebirds can become aware of those possible nesting sites. Since Bluebirds are partial migrants, which means they only migrate as far as they need to to find food, many overwinter and will use nestboxes to roost in on cold nights. Bluebirds usually begin to nest in late March or early April, depending on weather conditions. Bluebirds usually have two broods per season, but three broods are possible.
• Familiarize yourself with the nests of cavity-nesting birds so that you will recognize the species of bird using your nestbox. A Bluebird nest is made of dried grass or pine needles and is a neat square with a defined nest cup in the center. Bluebirds usually lay a clutch of 4 to 6 blue eggs though a small percentage of females lay white eggs.
• The incubation period for Bluebird eggs is 12 to 14 days. Nestlings remain in the nest an average of 18 days before they fledge.
• Fledglings depend on their parents to feed them for at least two or three weeks after fledging.
• Remove Bluebird nests and those of other birds as soon as the young birds have fledged.
• Keep records of the activity on your Bluebird trail. Use a notebook or jot your observations on a calendar. These notes are invaluable in helping to figure out what is happening with a nesting if something goes wrong.
• Don’t be discouraged if your nestboxes are not used the first year. If Bluebirds are not common in your area, it may take them a few seasons to find your new box. Bluebirds generally return to the same area each year. Bluebird trails have been an extremely effective method of reestablishing the Bluebird populations across North America.

Resources:
Lots of valuable Bluebird information can be found at www.sialis.org
The North American Bluebird Society (NABS)has Fact Sheets and other useful information at www.nabluebirdsociety.org
Nest Summary Worksheet from Cornell Lab of Ornithology Form for each nest monitored and each new nest attempt.
Cornell Lab of Ornithology’s “The Birdhouse Network” (TBN) is where you can click on the “instructions” tab to get more worksheets.
Cornell Lab of Ornithology home page
Check out our links page for access to more Bluebird information.