It's interesting to watch what happens when a tree dies," says Dr.
Kathryn Sieving, associate professor of wildlife ecology and
conservation at the University of Florida. "Here in the South, one of
the first species to take an interest in it is the pileated woodpecker.
"This woodpecker usually has several snags in its territory, and it
seems to visit them daily to test them until a snag ripens. A ripe snag
has decayed enough that it's easy to break apart and get into, plus it
has attracted a lot of invertebrates that would provide food for the
woodpecker," she explains.
Animals that use snags, either as their homes or as places to feed, can
be divided into two groups. First are the primary excavators, those
animals like the pileated woodpecker that dig into dead trees to create
holes and cavities. They're followed by secondary inhabitants, who come
along behind and use the holes and cavities the first group has
excavated.
The secondary group includes a number of birds and mammals. Birds
include tree swallows, chimney swifts, purple martins, bluebirds, some
flycatchers, titmice, some of the owls and a number of other avian
species. Ducks are also secondary cavity nesters.
Then there are the mammals. A number of squirrel species, particularly
flying squirrels, make their nests in cavities. And an occasional
raccoon or opossum may take up residence.