This article and podcast from Audubon explains why woodpeckers make cavities in trees during fall, even though they are not nesting at that time.

A familiar sound of spring: a woodpecker hard at work, carving out a nest hole in a tree trunk [woodpecker chiseling a nest hole]. Here the female will lay her eggs and the pair will raise their young. When you’re lucky, you can hear young woodpeckers, like these Pileated Woodpeckers begging from within the trunk.

But now that fall has arrived, we may hear an excavating sound again.

What’s going on?

It turns out that some woodpecker species stay year round in the region where they nest, while others migrate south in winter. Those that remain through the colder months – well, it’s safe to say they’re not nesting now. No, these fall excavators are chiseling out roosting cavities, snug hollows where they’ll shelter during the cold nights of fall and winter.

Many woodpeckers roost in such cavities, usually by themselves. Even the young, once they’re fledged, have to find their own winter quarters.

With woodpeckers, once the nights turn cold, it’s every bird for itself.