STREAMSIDE ATTRACTIONS Woodpeckers—A Keystone Species

​By Kevin Howe
​
​The woodpecker is a bird that I think everyone over the age of four can recognize--be it Woody Woodpecker (based on the Piliated Woodpecker) or a Yellow-bellied Sapsucker (a name I used a lot when I was a smart-aleck kid). While floating down the Dragon, we often see or hear a few woodpeckers, but we see hundreds of their nest cavities in the snags that line the sides of Dragon Run. (If you don’t know what a snag is, refer to the Streamside Attractions in our February 2022 issue located at DragonRun.org.)









​

Pileated Woodpecker
Photo by Betsy Washington

Snags you’ll see in the Dragon
Photo by Kevin Howe

Virginia is blessed with eight species of woodpeckers and each of our species are different in size, looks, and ecology. Worldwide we have 233 woodpecker species in every tree-containing habitat except Madagascar and Australia; there are even woodpeckers in some treeless environments of the southern hemisphere, not to mention our own southwestern desert Gila Woodpecker that often nests in saguaro cacti. Seven of the eight Virginia woodpeckers are found in the Dragon Run:  (29-inch wingspan), Northern Flicker, Red-headed, Red-bellied, Hairy, Yellow-Bellied Sapsucker, and Downy (12-inch wingspan). 

Woodpeckers are fascinating in every biological aspect of their being. Their ability to peck out a cavity in a tree at the rate of 100 to 900 strikes per minute is astounding (can you tap your finger as fast?).  But in doing so they subject their skull to a force 14 times greater than the force necessary cause a human a concussion or worse.  And their tongue is a marvel – it is about a third of the length of their body and so long it must wrap around the brain and may help cushion the brain. Further, their tongue has backward-facing barbs which help rake insects out of a narrow insect opening and into the bird’s mouth. Abundant sticky saliva helps as well. Their hearing is so keen that a woodpecker is said to be able to hear insects crawling and chewing beneath the bark and inside the tree.

​But from an ecologist’s perspective, nothing is more important and fascinating then their impact on the ecological community where they live. Biologists refer to woodpeckers as a keystone species. A keystone species is one which profoundly effects the environment where they live. Without that species, the community would be dramatically different. Any plant or animal may be viewed as a keystone species, and it is not always the most abundant or the largest. Some species are easy to see as a keystone species, such as the coast Redwoods of California and the African elephant. The keystone species concept is very useful to naturalists, ecologists, and conservation land managers interested in biodiversity. 

You might wonder what makes the woodpecker a keystone species.  Most of us don’t see a woodpecker that often and you rarely see many of them at the same time. Most everyone knows that woodpeckers are cavity nesters in trees. While lots of other birds are also cavity nesters including most owls, kestrels, chickadees, wrens, titmice, bluebirds, not to mention two celebrity birds of Dragon Run, the Prothonotary Warbler and the Wood Duck, all these birds rely, to a great extent, on a woodpecker species to create their nest cavity.  Although a few can do a little finish carpentry work to enhance the cavity and a few find a cavity created by a broken off tree branch,  most of the cavity creation is done by a woodpecker. By creating housing for birds and many other creatures, they are of the upmost importance in contributing to the biodiversity of their ecological communities.
​

Before going on about this, I need to lay down some facts about woodpeckers. All Virginia woodpeckers, with one exception, make their cavities in dead trees or dead areas of living-dying trees. They do not make cavities in live trees except for the endangered Red-cockaded Woodpecker, found in southeast Virginia’s longleaf pine forests; it makes its cavity nest only in a live pine, in fact, only in old growth (70+ year old), longleaf pines.

Each species makes entrance holes and nest cavities of different sizes which, as you might expect, attract different sized birds. A Chickadee or Titmouse loves the 1+ inch entrance hole made by the little six-inch Downy Woodpecker while the much larger Barred Owl needs at least a 7-inch hole–undoubtedly provided by a 16-inch Piliated Woodpecker. So, the different woodpecker species construct different sized cavities that end up appealing to different species of cavity nesters (often called secondary cavity nesters because they do not build the cavity).
​

Downy Woodpecker
Photo by Bruce Gillman©

Another factoid to add to this story is that many woodpeckers typically create a new nest cavity every year; thereby, creating another home for another cavity nester. Of further significance, researchers have found that when a woodpecker makes a cavity, this allows fungus to invade the heartwood of the tree which, over time, further enlarges the cavity.  As the cavities become larger, bigger birds move in thanks to both the woodpecker and the fungus.

So now let’s think about all of this for a minute— if the woodpeckers in an area disappeared for any reason, there would be no more woodpeckers making nest cavities. In time, probably 5-30 years, many other cavity nesting birds would disappear because their cavity trees would have rotted away with none of the original homebuilders to create new cavities. Without a supply of new woodpecker cavities, there would be no new generations, no cavity-nesting birds. Without question, woodpeckers are a keystone species. So are beavers, but I’ll save that story for another Streamside Attractions.

This scenario carries over to our own properties, especially in urban areas where you see few woodpeckers  and songbirds in developed areas that lack old trees or in manicured landscapes without dead trees or dead branches. And the same holds true for logged areas where snags and dead wood have been cleared and removed. Research indicates that the small Downy Woodpecker needs a 6”-8” diameter dead tree to make its cavity while the large Piliated needs one between 1’ and 3’ in diameter. So, if you see mostly a few of the same species in your yard, it may be because of a lack of nesting habitat.

Yellow-bellied Sapsucker.
Photo by Betsy Washington

​​In the last newsletter I quoted renowned forest ecologist, Jerry Franklin, “A dead tree is more alive than a living tree.” And that dead tree has a real deal with woodpeckers who create the holes and cavities (homes) that keep the cavity nesting birds around, not to mention harboring a large and diverse insect buffet for the community’s survival. Think about that next time you see a dead tree (snag) and smile at all the life inside it.
 
To see and hear these birds, go to Cornell University Ornithology.