There are cavities that don’t require a dentist and should never be filled.
A naturalist might be a better professional to call when you find a cavity tree. She could tell you who made it, who uses it and how it got there.
Cavity trees, sometimes also called den trees, can be living or dead trees (known as snags) that have holes of various sizes and shapes. These holes, or cavities, provide home, hearth, nursery, food and more to a large variety of creatures that make and use them.
Injuries are often what starts a hole or cavity and the further excavation of them can be natural or intentional. Natural ones may begin with a broken limb, fire or lighting and develop when regular rot caused by fungus or other factors follow the initial wound.
Animals can also start or further a tree cavity. Insect-seeking birds are well known cavity creators as they peck into the bark looking for insects. Woodpeckers know the drill.
Some trees are more inclined to the formation of a cavity than others. Beech, sycamore, black gum (known locally as beetlebung), maples, locust and sassafras are common cavity trees. Birds that can create these hollows are called primary cavity nesters. They include the usual suspects, woodpeckers, chickadees and red breasted nuthatches, among others. These species are the construction crew. Once the hole has been completed, tenants may follow these builders.
Secondary cavity dwellers are those animals that don’t create their own holes, but use ones that already exist. Some owls, kestrels, wood and other types of ducks, great crested flycatchers, bluebirds and mammals such as deer, raccoons, mice and squirrels, will also inhabit these holes.
Not all cavities are created equally — size, shape and location matter. It isn’t only the size of the hole, but the size of the tree that is telling. Certain animals prefer different tree diameters (holes size notwithstanding).
Smaller trees ranging in the six-to-eight-inch DBH (diameter at breast height) range attract downy woodpeckers, bluebirds, tufted titmice, house wrens and black capped chickadees. Going up a size from six inches to one foot in tree diameter would encourage saw whet owls, yellow-bellied sapsuckers, red breasted nuthatches, brown creepers and hairy woodpeckers.
Screech owls, northern flickers and great crested flycatcher enjoy the one-to-one-and-a-half-foot DBH trees. Trees that have a DBH that exceeds a foot and a half diameter are attractive to ducks, squirrels, bats and raccoons. Of course, hole size does come into play when bigger beasts try to get into smaller holes.
In total, more than one quarter of north eastern forest wildlife species need cavity trees, including 85 birds, and numerous mammals, reptiles, amphibians and invertebrates. These species use cavities for nesting and denning, (call those the tunnels of love), roosting, protection and feeding.
Sometimes multiple holes are created to provide various escape options for a bird that might need to flee from a different hole than their predators may be entering. That second or third cavity is that creature’s ace in the hole.
A healthy woodland and wildlife-friendly yard require cavity trees and dead, standing snags so consider keep a collection of those in your neighborhoods. So many species benefit and there are hole stories that can be told of the activities that occur just beyond the bark of your favorite tree.
Suzan Bellincampi is director of the Felix Neck Wildlife Sanctuary in Edgartown, and author of Martha’s Vineyard: A Field Guide to Island Nature and The Nature of Martha’s Vineyard.
