Cavity Nesters

The beautiful weather this week has me again peering out my window at the bird activity. Today especially, the birds that use the nest boxes (secondary cavity nesters) are busy at Tanglewood. Tree Swallows and Eastern Bluebirds are the main inhabitants of the nest boxes on our property.

What exactly is a cavity nester? It is a bird that uses a hole of some type to build a nest and raise young in. In North America there are approximately 650 different species of birds. Only 86 species nest in natural cavities. One way a natural cavity can be formed is by a primary nester excavating one. Woodpeckers are primary cavity nesters. A primary cavity nester excavates a new hole each breeding season. The holes are later occupied by other species of birds. Species of birds that rely on pre-existing holes are called secondary cavity nesters. Secondary cavity nesters include Bluebirds, Wrens, Swallows, Chickadees, Titmice and Flycatchers. Another way a natural cavity can be formed is by decay. High winds, lightning strikes, ice storms, insects, and fungal infection can all cause a tree to lose a limb or cause standing trees to die. Over time decay will set in causing a natural cavity. Birds like Chickadees will alter cavities of this type for their nesting needs.

Why would a bird use a cavity to place their nest in? The small entrance holes into the cavity protects birds from larger predators. Cavities also help protect from the extreme heat in the summertime and shelter from rain, snow and cold temperatures. Birds that use cavities have different physical and behavioral needs than open nesting birds. Cavity nesters have strong feet to cling to vertical surfaces of trees or nesting boxes. These birds also must be suited to entering and exploring small, dark spaces. Open nesting birds, such as Robins, will not explore a dark hole.

People cut down trees for firewood or for aesthetic reasons and so we tend to destroy many potential cavity nesting sites. We can make up for this by trying to leave dead or dying trees (also called "snags") standing when we can. We can also make nest boxes that, if made to the correct dimensions, make it easy to attract secondaray cavity-nesting birds.

For more information, come to Tanglewood this Saturday (April 19th) at 9:30 am for my Bluebird lecture and hike; there will be a PowerPoint presentation on Eastern Bluebirds (our state bird seen in photo above taken at Tanglewood by Vinnie Collins), and then we will head outside and check out the cavity nesters on Tanglewood's property. Wild Birds Unlimited from Corning will also be here with some nest boxes and Bluebird treats for those wishing to attract these beautiful birds to their properties. It's free and hopefully will be fun and educational. See you there!