"Cavity-nesting" is a term that describes birds that build nests, lay eggs and raise young inside sheltered chambers or cavities. Cavity-nesting does not typically apply to completely constructed cavities, such as birds that weave elaborate, enclosed nests, but instead is reserved for birds that rely on nesting shelter from other sources and build their nests within that shelter.
Types of Cavity Nesters
There are two types of cavity-nesting birds, depending on how they find a suitable nesting site:
- Primary cavity-nesting birds: These birds excavate their own holes, such as woodpeckers that drill out chambers in suitable trees or ground-nesting species that may dig out burrows in riverbanks. The labor to create a new cavity may take several days or weeks, depending on the birds' nesting needs.
- Secondary cavity-nesting birds: These species take advantage of natural or abandoned cavities, or in some cases will usurp them from other birds through aggressive intrusion. They may make minor adjustments to the cavity, such as adding or removing nesting material or changing the entrance but do not do substantial modifications.
Cavities Birds Use
The size, shape, and placement of cavities vary depending on the bird species and their individual nesting needs. Types of chambers birds may use include:
- Holes excavated in dead or decaying trees, stumps, logs, poles or large cacti
- Burrows in soft, vertical riverbanks, dirt mounds, dunes or similar banks
- Rock niches or crevices, either in natural cliffs or stone walls and structures
- Exposed pipes, chimneys or similar artificial cavities
- Supplemental nesting boxes and birdhouses
Some birds use a bare, empty chamber, while others line the floor or interior of the chamber with grass, twigs, wood chips, feathers, fur or other materials, even creating an entire nest within the chamber.
Familiar Cavity-Nesting Birds
Many birds will easily nest in cavities, and many bird families have at least a few members who are cavity nesters. Familiar examples include many woodpeckers, chickadees, parrots, nuthatches, trogons, flycatchers, wrens and bluebirds. Some ducks, such as the mandarin duck and wood duck, nest in cavities, as do some of the smaller raptors and owls. The American kestrel, barn owl, purple martin, great tit, and European robin are all common cavity-nesters.
Attracting Birds With Nesting Sites
Backyard birders can attract these birds by offering suitable nesting sites. Leaving old trees and dead snags available for primary cavity nesters can be successful, and adding birdhouses or nest boxes will help attract many secondary cavity nesters. Providing nesting materials for birds in spring will also encourage nesting activity nearby.
It is also important to be alert to birds using inappropriate cavities, such as dryer vents, chimneys, pipes, or other unsafe locations. In those instances, it may be best to discourage nesting birds, while encouraging them to use safer, more appropriate sites.
If birds do take up residence in a backyard cavity, whether it is a natural hole or a birdhouse, it is important to take steps to protect the nest from predators. Backyard birders may also want to monitor birdhouses to track which birds nest successfully, and watching a bird raise its family in the yard can be an enriching and rewarding experience.