By John Turner
One of the great joys of being a naturalist is to marvel at the countless adaptations, hiding in plain sight in the natural world surrounding us, that enable living things to survive and prosper. The tendrils of a catbrier, allowing the vine to attach and grow; the arching base of an earth star fungus to assist in spore dispersal; the burs of common burdock to facilitate the spread of seeds; and the sandpaper-like bottom of an osprey’s feet so it can better hold onto slippery prey, are but a few examples that come to mind of the hundreds of adaptations on display in the plant and animal species that share our island home.
You’d be hard-pressed to find a better group of animals to illustrate the value of adaptations - in their case a suite of adaptations - than woodpeckers, a group of birds which I’ve long marveled at and enjoyed watching. Their name is a bit of a misnomer as many woodpeckers do much more than just peck wood - they hammer it mightily with some species able to excavate cavities in living wood. Watch a crow-sized pileated woodpecker banging away on a downed log, making wood chips fly away in all directions as they search for little protein packets in the form of beetle grubs and you quickly appreciate the strength and power of these unique birds.
The adaptations that enable them to live a life intimately tied to wood, to make nesting and roosting cavities in it and to obtain grubs and other food items from it, are on display from their heads to the tip of their tails. The most obvious adaptation has to do with protecting the bird’s brain. According to the Peterson Reference Guide on Woodpeckers (a must read if you have an interest in this fascinating group of birds) a woodpecker may strike a tree trunk or branch as much as 12,000 times a day and perhaps more remarkably, it can involve a “g” force of 1,200 g, the equivalent of a human being slamming his/her head into a brick wall at 16 miles per hour! What enables them to do this with no ill effect is the thick and spongy bones of the skull, especially in the front and back of the skull.
Woodpecker tongues serve as further illustration of how well their anatomical features adapt them to survival. Some species have tongues that project from the tip of their bill as much as twice to three times the length of the bill itself, allowing the bird to probe deep into cracks and crevices. In some woodpeckers the tongue tip is sharp and harpoon-like and is edged with stiff, backward-pointing barbs to assist in the spearing of grubs as they retract the tongue upon contact with the beetle larvae. Further helping woodpeckers secure their prey is saliva that’s very sticky. In the case of the sapsuckers, their tongues are brush-like to help lap up tree sap.
Banging away on wood produces splinters that likely would get into bird’s nostrils and eyes. To prevent this some woodpeckers, such as the diminutive Downy Woodpecker, have evolved a set of bristles, highly modified feathers, that grow like tufts from the base of the bill shielding the nostrils and eyes. And speaking of eyes, woodpecker have several special adaptations that save their eyes from injury while their bill slams into wood. Most notably, this involves a particularly thick nictitating membrane – sometimes referred to as the third eyelid – which helps to keep the bird’s eye in its socket when rapid de-acceleration occurs the moment the bill strikes wood.
Woodpecker feet are also adapted to a clinging lifestyle. As you might guess they’re strong and typically have long, sharp and strongly-curved claws. But where they differ from typical perching birds is that typically two of their toes point forward and two point backwards, unlike perching birds that typically have three toes pointed forward and one pointing backward. This extra backward pointing toe, which the bird can turn sideways on thinner trunks and stems, helps the woodpecker better grip the tree bark.
Lastly, woodpecker tail feathers have also evolved to provide support. The two middle tail feathers are especially strong and stiff, much stiffer than a blue jay or robin’s tail feather. This stiffness is essential to provide support to the bird, forming a prop of sorts that helps to support the bird as it works it way up a tree.
As the woodpeckers illustrate, plant and animals have developed a wide range of adaptations that enable them to survive. It’s fun, as you explore the world around you on hikes through woodlands and along shorelines, to make an effort to identify some of them. They may be anatomical or behavioral but when you do see them in action take a moment to marvel.
Photo of Red-headed Woodpecker by Delee Smith - All Rights Reserved