PARRY SOUND — Have you ever noticed a hole or two in the trunk of a tree? These holes, also known as cavities, are incredibly important. Over 50 species of birds and mammals in Ontario depend on cavities in trees for countless purposes. These holes are used for feeding, nesting, roosting, storing food, denning, escaping predators, providing shelter, raising young, and hibernating.

Although cavities occur naturally, many are also created by hardworking birds like woodpeckers, chickadees, and the red-breasted nuthatch. A common cavity created by a woodpecker is a feeding cavity. These cavities are 5-20 cm deep and often have a rectangular or irregular shape with rough edges. If you see at least two oval-shaped cavities in a large hollow tree, it may be a roost cavity for pileated woodpeckers. There are at least two holes so that the bird can escape if a predator comes. Cavities for nesting tend to have circular entrances as well but this time the woodpecker has hollowed out a chamber inside the tree. Rarely are two nest holes less than 1 m apart. Nest cavities can also form when a branch dies and leaves a more irregular hole.

Many excavating birds do not use the same nest cavity twice. This allows many other birds and mammals including the saw whet owl, kestrel, eastern bluebird, deer mouse, marten, and fisher to move in. Other wildlife can also use natural cavities called escape cavities as shelter or protection from predators. These are not suitable for roosting or denning because of their size or where they are found. Escape cavities could include natural openings at ground level or hollow trees with large seams.

Cavities are often found on less vigorous or declining trees. In managed forests, the least healthy trees are usually removed first so that the forest can improve and thrive. So how are local foresters ensuring that these important habitat features remain in our crown forests? Westwind Forest Stewardship Inc., that manages forested Crown land in the Muskoka-Parry Sound region, ensures that at least a prescribed minimum number of cavity trees are being maintained. Certified tree markers are selecting good cavity trees to stay. By putting a blue spray paint “W” or dot on a tree, they let operators know that this tree cannot be harvested.

All cavity trees, however, are not created equal. Trees with nest or roost cavities are more valuable for wildlife than feeding or escape cavities. More valuable cavity trees are prioritized when selecting wildlife trees to keep in a stand. Sometimes, like in the case of roost cavities, there is even a harvest-free reserve put around the tree to further protect it.

So why don’t dentists like foresters? Because we keep too many cavities.


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