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Natural North Dakota

Cavity Nesting Birds

I was sitting on a downed tree in the Turtle Mountain aspen forest recently when a chickadee seemingly emerged from the trunk of a nearby aspen with something in its mouth. It flew to a nearby tree, dropped the object, then flew back into the tree. This was repeated several times.

It was quickly apparent that this bird was either excavating or cleaning out its nesting cavity. I would never have spotted the cavity without seeing the chickadee travel back and forth. Actually, it took a couple trips by the chickadee before I could spot the cavity where a small branch had been broken off and rotted a bit.

Birds choose different locations for nesting. And one of the factors in nest site selection is to choose a site relatively safe from predators. Many birds carefully place their nests well hidden amongst the foliage of trees and shrubs, or on the ground. And some construct their nests inside a tree! What could be better?

Woodpeckers, of course, excavate their own nest cavities. Many other birds, however, utilize an existing cavity. The list of these birds might surprise you, and includes house wren, bluebirds, chickadees, nuthatches, purple martins, owls, wood ducks, as well as mergansers, buffleheads, and goldeneyes, and the kestrel or sparrow hawk.

House wrens commonly utilize bird houses, and a bird house is nothing more than a fancy constructed nesting cavity. We have several wren houses in our yard, along with a wren house with an entrance hole that is a little larger than most, which has been claimed by a pair of tree swallows over the past few years.

It might surprise you, but natural nesting cavities are generally in short supply. We are perhaps a bit too efficient at taking down dead or dying trees. I was rather surprised to see an article by the Virginia Department of Forestry suggesting cavity trees for woodlots. They suggest 10-20 live or dead small cavity trees (<12 inch diameter) and 2-5 larger trees (>12 inches diameter) per acre be left on woodlots for cavity nesters.

So, consider putting up some bird houses. And the next time you see a chickadee or other cavity nester flitting around, you might consider observing it for a bit to see if you can find a nest cavity. And if you have some trees that are dead or dying, consider leaving them for the birds if possible.

~ Chuck Lura

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