Avian Architects: Part 5

CAVITY
About 85 species in North America make nests using cavities, birdhouses, gaps in structures or holes found in tree hollows, telephone poles, abandoned buildings and more.

Of the birds that use nest cavities, most woodpeckers (Picidae) including the northern flicker [Colaptes auratus] and red-naped sapsucker [Sphyrapicus nuchalis] tend to be the species that do the hard work of excavating many of the tree cavities. Fewer birds excavate their own holes in trees. But of those that do, the woodpeckers are by far the best known. The cavity using opportunists include bluebirds (Sialia), chickadees (Paridae), house sparrows, house wrens [Troglodytes aedon], nuthatches (Sitta), the bridled titmouse [Baeolophus wollweberi], violet-green swallows [Tachycineta thalassina], many parrots, and even some small owls such as the northern saw-whet owl [Aegolius acadicus]. Red-cockaded woodpeckers nest in cavities that can take years to construct in a living tree. They live in groups and will have as many as four helpers. These birds choose cavities that accommodate their species-specific size.

Cavity-nesting birds are common and will either excavate their nesting cavities in soft, decaying wood or use natural cavities in trees, snags, or cacti. Often these excavated holes are tunnel or chamber-like, extending downward into the tree. The interior cavity may be bare or lined with a variety of materials such as grasses, sawdust, fur, moss, or shredded bark materials. This lining may form a cup-like nest to further protect the eggs and hatchlings.

Making a nest in a hole that already exists in a tree is not really an architectural feat, as it involves little effort on the bird’s behalf. Still, holes in trees, alive or dead, make excellent nest sites and numerous birds use them.

Once the job is done it’ll soon be time to handle the hardest work. Raise those kids!

Some, like this House Wren [Troglodytes aedon] and several of its relatives, as well as various Flycatchers use existing holes to nest in. They make very little modification to the hole except to supply some lining as nest material. Others, like the many hole nesting Parrots and the Pygmy Nuthatch [Sitta pygmaea] and their relatives, will modify existing holes to varying degrees.

Other tree cavities aren’t necessarily created by other birds. In this example, these white -breasted nuthatches have taken up residence in a natural decaying cavity in an old but living pine tree.

From taking advantage of tree cavities drilled out by woodpeckers to human made creations, bluebirds and some swallows, wrens and chickadees will delight in taking residence in a bird house. We’ve seen violet-green swallows compete with both mountain and western bluebirds for one of these and will use that box year after year. Chipmunks also move in when given the opportunity.

Same bird house, different residents.

And any house will do. House Wrens will fill up a bird house until it’s overflowing with twigs. They will also fill other nest boxes with twigs before settling on a site.

It’s a cooperative effort when it comes to satisfying hungry kids.

And feeding young can be hazardous! Expecting more, this demanding chick grabs onto the beak of the adult.

Coming soon…… Pendant, Dome and Spheres