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Attracting Bluebirds and Other Cavity
Nesting Songbirds in North Dakota

Controlling Competitors and Predators


The goal of establishing a bluebird trail is to attract as many bluebirds as possible. There are obstacles that you will encounter with this goal in mind and an understanding of the threat should assist you in maximizing your bluebird return.

Some people consider tree swallows and house wrens as nuisance birds. In actuality, these birds are beneficial for insect control and they are protected by law. As discussed earlier, avoid placing boxes in habitat areas favored by these species. Generally, the closer to wooded habitat, the more likely you will attract these two birds.

House sparrows are the largest competitor of bluebirds and concern over their competition is justified. House sparrows are aggressive and out compete bluebirds for nesting space. They will actually destroy and dump eggs from a bluebird nest and kill both young and adult birds when encountered.

GIF - Damaged eggs
Three bluebird eggs are shown above after being pecked and thrown out of a bluebird nest box by a house sparrow. House sparrows are the largest competitors of bluebirds and they should be controlled.

The best method of preventing this from happening is to avoid placing boxes in areas close to known sparrow habitat-usually urban areas, farmyards and any other location close to human dwellings.

Next, monitor nest boxes closely and remove sparrow nests immediately upon initiation. If you observe house sparrows beginning to build a nest in a particular nest box, there are devices which can be attached to the entrance of the nest box which trap the live bird inside. Once caught, they can be destroyed. There are also large live traps available on the commercial market which will trap numerous birds at once and can be successful in removing local house sparrow populations.


In addition to damages that may be caused by other songbirds, a number of other wildlife species, domestic cats, and insects can be potentially harmful to bluebird production.

Even though predation is part of nature, steps can be taken to lessen the amount, especially in the case of domestic cats which are not part of nature and can be controlled. Raccoons, snakes and cats all must enter the nest box by climbing unless they can reach nest boxes by jumping from tree limbs or other objects that are located too close. By wrapping an apron guard made of sheet metal around the post about a foot under the nest box or by placing a four inch piece of PVC around the post, these species will not be able to access the nest box at all.

GIF - Snake in box
Predators such as the bullsnake shown above, however very beneficial in controlling mice and other rodents, can take bluebirds and their eggs. Other predators such as domestic cats and raccoons can also prey on bluebirds. All of these predators can be controlled by using predators guards as shown below.

To prevent predators from reaching inside the boxes, a Noel nest hole extension can be used. The above referenced predator guards can be made from materials purchased locally and are illustrated below.

GIF - Predator battles

Hawks such as the cooper's and sharp-shinned and falcons like the kestrel eat songbirds including bluebirds. Again, this is entirely natural and should not alarm you. Hawks and falcons are only doing what they do to survive and this must be accepted. Bluebird losses can be limited by avoiding the placement of nest boxes underneath perches such as high line wires or in known raptor nesting areas.

Blowflies are a type of fly that lay their eggs in bird nests. The larvae that hatch from these eggs will feed by sucking blood from the young birds. Larvae will feed during the night and crawl back into nesting material during the day. To check for larvae, lift up the bottom of the nest and tap it gently. If you find any larvae, brush them out. If larvae are in extremely high numbers, discard all the old nesting materials, brush out the box, and fashion a new nest with fine grasses. Replace the nest and return the eggs.

Paper wasps and yellow jackets may also decide to take up residency in a nest box. Check on the bottom side of the roof when the temperature is cool in the evenings.

Insect nests can be scraped out with a putty knife or knocked out with a stick. Do not use commercial sprays. A solution of 0.1 Pyrethrin can be used without having toxic effect upon the birds. Simply spray the solution through the nest hole opening in the front door.

Previous Section -- Other Songbirds Utilizing Bluebird Trails
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