When many people think of birds’ nests, they picture a woven basket tucked into a shrub or perched on branches. But some birds take a different approach—they nest in cavities, either natural holes in trees or ones excavated by woodpeckers. In North America, about 85 bird species are cavity nesters.

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Cavity nesters fall into two groups: primary and secondary. Primary nesters, like woodpeckers, chickadees, and red-breasted nuthatches, excavate their own cavities using their strong beaks. Even among these, there are differences: strong excavators, such as woodpeckers, can peck into both hard and soft wood, while weaker excavators, like chickadees, need softer or rotting wood.

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Secondary nesters, on the other hand, don’t create their own cavities. They rely on natural holes or cavities made by primary nesters. Birds like swallows, owls, titmice, and others fall into this group. Once a cavity has been located or excavated, it serves multiple purposes: it can be a nest for eggs and young, a roost, or a shelter.

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Unfortunately, suitable cavities have become prime real estate. Habitat loss, selective removal of dead or dying trees, and competition from aggressive non-native species have made cavities harder to find. English House Sparrows and European Starlings are both cavity nesters and highly aggressive. House Sparrows may even kill bluebirds in their boxes, and starlings have been known to kill adult Red-bellied Woodpeckers—normally dominant at feeders—to take over a cavity.

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What Can You Do?

Install a nest box! Start by identifying the birds in your yard and researching which species are likely to use a box. For example, Red-bellied Woodpeckers usually won’t, but Northern Flickers will. Chickadees take to nest boxes as well as House and Carolina Wrens, Eastern Screech Owls, and even Wood Ducks (if you have the habitat).

See Eastern Bluebirds around your place? Get those nest boxes up!

 

The key is choosing a well-designed nest box. Factors like box size, entrance hole diameter, placement, drainage, and ventilation all influence whether the species you want will take up residence.

 

A great starting point for research is NestWatch.org, which provides recommended dimensions and other guidance.

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By providing a thoughtfully designed nest box, you can help give birds a safe place to nest, roost, and raise their young—and become part of the solution to cavity competition in your area.

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