Apr 15, 2020 | Featured in: Watching Backyard Birds, April 2020

Bluebird Boxes and Spring Housecleaning

A western bluebird flies into a backyard nest box.

To clean or not to clean last year's nest from a bluebird box in preparation for nesting this spring—that is the question.

Research shows that bluebirds, when given the choice, overwhelmingly select boxes with an old nest in it. This goes against a popular thought that bluebirds avoid old nests due to parasitic blowfly larvae. Blowflies lay their eggs in old nests, and the larvae attack the young birds.

However, researchers say that although there is a much greater chance of blowflies in boxes with old nests, there is also a much greater chance that parasitic wasps will lay eggs in the old nests. The wasps prey on the blowflies, limiting the damage they do. The researchers also point out that bluebirds might choose boxes with old nests because the birds spend less time and energy finding nesting material.

But neither of those reasons justify failing to monitor, maintain, and even clean your nest boxes. Removing an old nest removes mites, other parasites, and feces, as well as blowfly eggs. Watching Backyard Birds recommends emptying and cleaning your nest boxes soon—before nesting season starts. Remove the old nest; sweep out residual waste material, and you're done. Do not use pesticides or cleaning solutions in the nest box. Harsh chemicals can leave residue that may harm birds, especially nestlings.

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