Nature Smart Column with Stan Tekiela: Woodpecker Cavities

A cavity in a tree, excavated by a woodpecker, seems normal enough. But when you stop to think about it, this simple space is absolutely remarkable. Today, let’s take a closer look at the humble woodpecker cavity.

According to the International Ornithological Committee (IOC), there are 241 species of woodpeckers in the world. Here in America, we have 22 species of woodpeckers, ranging from the small downy woodpecker to the giant pileated woodpecker. All these woodpeckers have one thing in common: They all excavate cavities to use for nesting. Because of this, woodpeckers are considered primary cavity-nesting birds. In other words, woodpeckers are the primary users of the cavities that they excavate; however, there are an estimated 75–80 species of non-woodpeckers that also rely on these cavities to nest. These birds are called secondary cavity nesters, and their very existence depends upon woodpeckers. A study published in 2017 found that nearly 20% of all bird species in the world rely on cavities in trees, for roosting or nesting.

Most woodpeckers only use the cavities that they excavate for one brood of young birds. Woodpeckers excavate in dead or dying trees with just a few exceptions. Live trees/wood are too dense and hard for the woodpeckers to excavate. Over the life span of the cavity, it may host dozens of families of baby birds from a wide variety of secondary cavity nesters.

Depending upon the woodpecker species, or the softness of the wood, it takes anywhere from 4 to 20 days for a pair of woodpeckers to excavate a cavity. I say “a pair” because both the male and female do the work. It all depends upon the level of decay in the wood. Obviously, the softer the wood, the faster the process goes. Only a small handful of woodpecker species excavate cavities in live trees. The overwhelming majority are excavated in dead trees or dead limbs of live trees.

In the world of woodpeckers, parenting duties are shared by both adults. Cavities are excavated by both male and female, but the male does slightly more work. When it comes to incubation, the female does most of the incubating during the day, and the male takes the night shift. After the young hatch, both parents bring food to the begging babies.

So many of our most beloved birds—eastern bluebirds and mountain bluebirds—as well as raptors—American kestrels and screech-owls—are dependent upon large woodpecker cavities. In one recent study, it was found that, of all the cavities found in a forest, only 10% of the natural cavities were being used, but 80% of old woodpecker cavities were being utilized by secondary cavity-nesting birds. I think many people do not realize that several waterfowl species, such as hooded mergansers, wood ducks, and buffleheads, also depend upon cavities in trees to nest.

So far, I have been concentrating on nesting and haven’t considered the value of woodpecker cavities for roosting at night. Many species of birds who don’t use cavities for nesting will use a nest cavity for a place to be safe and warm when roosting, especially on long, cold winter nights. Many studies show the benefits of roosting inside cavities compared to being out on a tree branch, which leaves birds vulnerable to nocturnal predators like owls.

And speaking of owls, all the species of screech-owls use woodpecker cavities to nest and also roost, except they roost during the day. All of this was running through my head the other day while I was capturing some images and video of a wonderful eastern screech-owl that I found enjoying a little sunshine on a cold winter day in the northland. Until next time…

Stan Tekiela is an author, naturalist, and photographer who travels extensively to study and capture images of wildlife. He can be followed on www.instagram.com and www.facebook.com. He can be contacted via his webpage at www.naturesmart.com.