Other smaller nests can be made of materials such as grasses, animal hair, plant stems, bark strips, lichens and spider webbing. With chimney sifts, secretions from the bird's mouth are used to glue twigs to the inside walls of chimneys. Some birds, such as owls, never make their own nests but are more likely to use an old nest of another large bird such as a crow or hawk. Woodpeckers, chickadees and titmice excavate holes in trees. Chickadees and titmice then also line the nest with other materials.
Woodpeckers just use the wood chips at the bottom of the nest.
There is another group of birds that nest in tree holes, but cannot excavate the holes themselves. These include bluebirds, nuthatches, many wrens, some swallows and some owls. They are dependent upon the excavators for their nest sites, an this is why it is a good conservation measure to leave dead trees standing if they have nest holes in them. They will be useful to the birds. Feathers - Hummingbirds have no downy feathers at all.