Posted: February 9, 2023
Pileated Woodpecker. These primary cavity nesters excavate distinctive oblong nest holes about 3-1/2” long in dead or dying large trees. Photo© courtesy of Mike and Laura Jackson. Used with permission.
By Paul J. Solomon and Jeanne M. Riley
Birds! What would life be without them? They enrich our lives with their beauty and song. They are active in controlling insect pests, pollinating plants, spreading seeds, and removing carrion from our surroundings. Birds have the largest following of all wildlife in the U.S., with over 45 million people reporting they observe wild birds, per 2016 U.S. Fish and Wildlife Service reports. Many of the birds that populate our communities rely on tree cavities for nesting or roosting, cavities which are increasingly in short supply due to forest clearing and fragmentation carried out for agriculture, logging, and land development. Firewood cutting, fencerow removal, and the rising use of steel and plastic (versus wooden) fence posts also reduce the number of nesting cavities. Of the 190 species of breeding birds in Pennsylvania, approximately 35 are cavity nesters. One-half of these are primary cavity nesters, such as woodpeckers, that excavate their own nests as part of their breeding behavior. Secondary cavity nesters—such as wrens, Eastern Bluebirds, American kestrels, Tufted Titmice, chickadees, Purple Martins, and Great-crested Flycatchers—rely on pre-existing holes as nest sites. Cavities, both natural and manufactured, offer a number of benefits to birds. They provide protection from predators, extreme weather, and disease as well as space for food storage. Use of cavity nests has been shown to extend nesting time and success, with 60% to 80% of cavity nests supporting the birth of at least one young bird, versus 20% to 40% of open nests. Use of nesting cavities also enables birds to conserve energy in cold weather. Without nesting cavities, roosting birds such as robins can burn one-tenth of their body weight to stay alive in the winter. By maintaining snags and providing nesting boxes, landowners can attract and sustain the many species of birds that are vital contributors to the ecosystem on which we all depend.
Snags. Snags are dead or dying trees which contain cavities used as nesting sites by wildlife. Snags of both deciduous and conifer (evergreen) trees are used by wildlife. Hard snags, which are partially or recently dead trees, typically have their bark intact and feature solid or mostly undecayed wood. These kinds of snags are well-suited to cavity excavating birds such as woodpeckers. Other species prefer soft snags, which are in advanced stages of decay and generally do not have limbs. Dead or dying trees with large diameters, existing holes or cavities, wounds or scars, and a combination of decayed and sound wood are ideally suited for nesting. Landowners wishing to attract diverse species of birds should maintain snags of a variety of types and sizes. Potential future snags should be identified and saved when undertaking logging or forest management activities. However, for safety considerations, snags located near buildings, particularly residential units, should be removed during logging operations. Nesting Boxes. Nesting boxes can be built from plans or kits or can be purchased. Unfortunately, many commercially manufactured bird houses are designed to attract a buyer rather than a bird. Nesting boxes which are not properly designed do not adequately protect birds, and therefore should be avoided. Nesting boxes should be designed, constructed, and placed with a particular species of bird in mind. Eliminating predators’ access to boxes is also important in creating nesting habitat. Features to consider in choosing or constructing a nesting box and tools available to protect it from predators are described in the table below. Boxes with these characteristics protect nests from extreme temperatures, driving rains, and predators. Perches on nesting boxes should be avoided. Birds that use nesting boxes have strong feet and do not require them, and perches can make it easy for predatory birds to access the box. Common preferred nesting locations include open woods and edges (chickadee), wooded swamps and streams (Prothonotary Warbler), woodland edges (Tufted Titmouse), old field and brush (Carolina Wren), open fields (Tree Swallow), and forest openings and edges (Downy and Hairy Woodpeckers).
Features to Consider in Nesting Box Design, Construction, Placement, and Protection
Some cavity nesters, such as Eastern Bluebirds, prefer nesting boxes which already contain suitable nesting material. Nesting material may enhance the attractiveness of the box, provided it is free of parasite infestation. Investigate the preferences of the species of interest when installing the box. New nesting boxes are best installed just before breeding season. They can be kept up all year long, as they can be very useful to birds for conserving heat in the colder months. Birds may be hesitant to accept a new nesting box, so experts advise leaving the box in place for two to three years before modifying or moving it. Some species like used nests and so may be attracted to existing nesting boxes. Boxes should be inspected in late winter and maintained according to the needs of the species of interest. Native bird populations play many essential roles within an ecosystem but are increasingly under threat. With thoughtful design, construction, placement, and protection of natural and manufactured nesting boxes, we can provide native bird populations with the welcoming homes they need to thrive and thereby ensure that they continue to enrich our natural world. Let’s get to work!
Black-Capped Chickadee
Although these tiny birds will nest in existing cavities, they also will excavate their own nests in soft snags. Their persistence in building nesting cavities is amazing!
Photo© courtesy of Mike and Laura Jackson. Used with permission.
Eastern Bluebird
This species was brought back from the edge of extinction when DDT was banned and volunteers across the U.S. built thousands of nesting boxes for this cavity nester.
Photo© courtesy of Mike and Laura Jackson. Used with permission.
James C. Finley Center for Private Forests
Address
416 Forest Resources BuildingUniversity Park, PA 16802
- Email PrivateForests@psu.edu
- Office 814-863-0401
- Fax 814-865-6275
James C. Finley Center for Private Forests
Address
416 Forest Resources BuildingUniversity Park, PA 16802
- Email PrivateForests@psu.edu
- Office 814-863-0401
- Fax 814-865-6275