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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. Wooden fence posts that 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 chase away the more timid Bluebird. 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 Bluebird 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 box 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.
  • Oval holes should measure 1 3/8" x 2 1/4" for the Eastern Bluebird.
Mounting the Bluebird Nestbox

Smooth round pipe is probably the best and simplest mounting system to use -- 3/4" electrical conduit works well, but any smooth scrap round pipe will also work

  • Coating the pole with grease will also help to keep predators off the box.
  • Hardware cloth placed under a box helps to prevent snake predation.
  • Unless your trail is in an area where raccoons are not present, avoid mounting Bluebird boxes on a fence line or on trees. Raccoons are known to walk fence lines and may find your boxes.

Habitat is the key factor to consider when setting up a Bluebird trail. Open rural country with scattered trees and low or sparse ground cover 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 nesting boxes. If Bluebirds do not like the habitat, they probably 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 first leave the box. 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 chance of survival.
  • Always remove House Sparrow nests immediately.
  • Have your Bluebird boxes in place by mid-March when the Bluebirds return from their winter migration and are looking for nesting sites. However, boxes may also be put up later in the nesting season.
  • Bluebirds usually nest in late March or early April, depending on weather conditions. In southern states, where Bluebirds reside year round, nesting may occur earlier.
  • Bluebirds usually have two broods per season, but three broods are possible.
  • Recognize a Bluebird nest -- It is a cup-shaped nest that is usually made up of 100% woven grass. Pine needles may be used.
  • Bluebirds usually lay 4 to 5 light blue eggs, but may lay as many as 6 or 7. A small percentage of their eggs may be white.
  • The incubation period for Bluebird eggs is 12 to 14 days.
  • Nestlings remain in the nest 16 to 21 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.
Don't be discouraged if your nesting boxes 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.

Getting Started text taken from JennaBird.com

It is highly educational to look at the series of pictures showing a family of Bluebirds on a daily basis from before laying eggs till the empty nest, a period of over 30 days.  These pictures by Bet Zimmerman can be found on this link.

For your convenience, we have available the Nest Summary Worksheet from Cornell Lab of Ornithology Form for each nest monitored and each new nest attempt on this page.

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.


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