Key Traits
Several outstanding features make woodpeckers so easy to tell apart from other birds. Let’s quickly go over these features now and then I’ll get into more detail on some of them later.
The first feature is the fact that, well, woodpeckers peck wood. The name says it all. In Spanish, a woodpecker is called a pájaro carpintero—a carpenter bird. I imagine that in most languages the name for these birds captures the wood-destroying aspect of their behavior.
Woodpeckers have a straight, chisel-shaped bill. This is a finely-honed tool for excavating wood. What they’re looking for beneath the surface are insects to eat. A long, thin tongue helps them snatch bugs out of little crevices and tunnels they expose in rotting wood.
The posture and movements of woodpeckers are distinct. They tend to hitch themselves up tree trunks while in an upright posture. These movements often look herky-jerky.
And when woodpeckers fly, many of them have a bounding or undulating flight path, where they rise a little as they flap their wings and fall a little between bursts of flapping.
Stiff tail feathers and strong feet allow a woodpecker to brace itself against a tree while whacking at the wood.
Besides digging for insects to eat, woodpeckers also use their bills for communication and for excavating their nests. They communicate with each other by drumming against wood to make a loud sound. Drumming is one of their unique features. And all woodpeckers are cavity nesters. Most of them create their nests by chipping out a deep hole in wood.
Many woodpecker species have bold black-and-white coloration, on just the head or over most of the body. Splashes of red and yellow are common. And quite a few species have greenish wings. Despite these general patterns, there’s plenty of color variation across this diverse bird family. There’s no one pattern seen in all woodpeckers.
Evolution
Millions of years ago, the ancestor of all woodpeckers figured out how to access a rich and mostly untapped resource: juicy and nutritious bugs burrowing around in wood. Natural selection favored individual birds that were better at digging into wood and capturing prey. And so the woodpecker was born and the world has never been the same.
Today, there’s a boatload of woodpecker species. They’ve been successful in their unique lifestyle, their niche. They have adaptations that make them really good at what they do. Most of the salient features of woodpeckers that we just talked about relate to their special adaptations.
But these traits didn’t appear all at once in prehistoric woodpeckers. It took a long time. A study published in 2012 offers a model for the stepwise evolution of traits that allowed woodpeckers to become more and more specialized.
By analyzing anatomical and behavioral data from across most of the modern woodpecker lineages, the researchers in that study came up with this progression:
The earliest woodpeckers could drill into wood to find bugs, but they didn’t have strong enough skulls to excavate their own nests. And they couldn’t climb up tree trunks. In the next step, they developed reinforced, tougher skulls and bills. That allowed them to hollow out their nests. In the last steps, their toes moved into their modern arrangement and their tail feathers got stiffer. With strong, grippy feet and a rigid tail, they developed a support structure that allows for tree trunk climbing shenanigans.
Now let’s rewind to those very first, ancestral woodpeckers. Where did they live? The actual geographic origin of woodpeckers is still a mystery. Scientists have been using fossils, comparative anatomy, geographic distribution, and DNA sequences to figure out where and when woodpeckers first hopped onto the scene.
The reason we can’t say for sure where these birds originated is because different lines of evidence support wildly different scenarios. For example, if you look at the high species diversity of the relatively primitive piculets in South America, that would suggest that the woodpecker family got its start on that continent. But there are a few older but less diverse lineages in the Old World. And that’s also where the oldest woodpecker fossils have been found.
The most likely origin story for woodpeckers is that they first evolved in the tropics of Eurasia, about 45 million years ago. Around that time, the ancestor of all woodpeckers became a distinct creature, splitting off from the lineage that became the modern honeyguides. Honeyguides live in Africa and Southeast Asia. They’re the closest living relatives of woodpeckers.
The oldest woodpecker fossil we’ve discovered is a leg bone from Germany. It’s from a bird that lived about 25 million years ago, during the late Oligocene Epoch. So this is one of those fossils that supports the Eurasian origin of woodpeckers. The earliest evidence of woodpeckers from the Western Hemisphere is a feather suspended in amber from the Dominican Republic in the Caribbean. That fossil is from about 23 million years ago.
Woodpecker evolution and species diversification really got cooking starting around 14 million years ago. They spread around the world and evolved into hundreds of species. They came into their own, occupying their specialized niche as arboreal, forest-dwelling, tree-drilling, bug-eating machines.
Diversity and Distribution
The woodpecker family, Picidae, is diverse. Depending on the list you look at, there are something like 234 to 254 species in this family. Not too shabby.
The name of the family comes from the Latin word picus, which means woodpecker. Fair enough. And picus probably came from a related Latin word, picco, meaning to strike or peck. This is just stuff I dug up on the World Wide Web and found interesting… If you’re a scholar of Latin etymology, please email me and tell me how very wrong I am.
The family Picidae has three—or quite possibly four—distinct subfamilies. The two species of wrynecks make up one subfamily. Then, there are about 30 species of piculets. From their name, you can guess that piculets are tiny little nugget-like woodpeckers. They have stubby bills and short-tails. The so-called “true” woodpeckers make up the last and largest of the subfamilies. There are about 200 species.
Genetic data indicates that one piculet species, the Antillean Piculet, is divergent enough that it probably should be assigned to its own subfamily within the woodpecker family. This unique bird lives on the island of Hispaniola in the Caribbean.
The smallest woodpecker in the world might be the Bar-breasted Piculet that lives in the Amazon Basin of South America. This little bird is only 3 inches long, which is 7.5 centimeters. That’s not much larger than some hummingbirds.
At the other extreme is the Great Slaty Woodpecker. This beefy beast is up to 20 inches long (50 centimeters) and can weigh about 1.25 pounds or 560 grams. Doesn’t sound very heavy, but hey—it’s a bird.
This long-necked, long-billed woodpecker is almost entirely gray-colored. It lives in Southeast Asia.
Speaking of necks, in my neck of the woods we have the Pileated Woodpecker. It’s the largest member of the Picidae family in North America. It’s about the size of your standard-issue crow. I love hearing and seeing these big black, white, and red birds in the forest. They kind of remind me of something prehistoric, like a little pterodactyl.
The 240 or so woodpecker species are mostly creatures of the forest, but members of this group can be found across a wide variety of habitats. Some live in open woodlands or savannas, others live in grasslands or deserts.
A handful of species have even evolved to have a terrestrial lifestyle, foraging in the dirt or grass rather than on tree trunks. These species tend to live in open areas with few trees. A few, like the Ground Woodpecker of southern Africa and the Campo Flicker of South America, dig their nest cavities in the ground. The ancestors of these birds were tree-dwellers, so this earth-bound existence evolved secondarily. Fascinating!
Woodpeckers live in all these arboreal and terrestrial habitats across most, but not all of the world. They are conspicuously absent from Madagascar, New Guinea, Australia, and New Zealand. They aren’t on Antarctica either, but that almost goes without saying. Not so many trees down there...
This biogeographic pattern is a little surprising. I mean, woodpeckers managed to get everywhere else, right? One explanation is that maybe woodpeckers are very reluctant to fly long distances over water, over stretches of open sea.
Like so many other animals, woodpeckers have been prevented from dispersing into New Guinea and Australia by a stretch of open water east of Bali and Borneo. This marks what we call Wallace’s Line, see my blog on the Wallace Line [link to blog]. This biogeographic dividing line or barrier was first described by Alfred Russell Wallace, the Nineteenth Century naturalist who discovered natural selection at the same time Darwin did. Animals and plants on either side of the line are very different. Only three woodpecker species live east of it.
The hypothesis that dispersal has been restricted by oceanic barriers explains some geographic patterns in woodpeckers, but certainly not all of them. It’s not perfect.
But now let’s look at the places where woodpeckers have been able to get to. Here’s a quick breakdown of their diversity, continent by continent.
We have 60 species here in North America. The most commonly observed are the Downies, which are our smallest woodpeckers and they’re regular visitors to backyard feeders.
South America has the highest diversity of any continent, with between 85 and 92 species. The Green-barred Woodpecker, Red-crowned Woodpecker, and Campo Flicker are the most common species there.
In Europe, you’re most likely to see Great Spotted, Green, and Black woodpeckers. There are 9 other species living on that continent. So a total of 12. Only 4 are found in the United Kingdom.
Interestingly, the African continent has just 33 woodpecker species. The most widespread and commonly seen is the Cardinal Woodpecker.
Woodpeckers in Asia are almost as diverse as they are in South America. There are between 75 and 80 species in Asia. Of course, the birds of Europe and Asia have some overlap, so it’s not a shock to find that the Great Spotted Woodpecker is the most commonly recorded species on both continents. The Gray-headed and White-backed woodpeckers are the next most common species in Asia.
Foraging
Let’s consider the Red-bellied woodpecker which has a bright red crown and nape and a cream-colored body. Its wings are black with bold white barring. The belly has only a faint, almost imperceptible, pink wash. So maybe Red-bellied Woodpecker wasn’t the best name for this species.
This bird will spend the daylight hours as it does almost every day of its life: searching for food. It will be continuously active as it forages in the forest.
Landing on the trunk of a big oak tree, the woodpecker clings to the vertical bark surface. Most birds can’t do this so easily, if at all. But woodpeckers have specialized feet and tail feathers, allowing them to rest comfortably on vertical trunks.
Strong feet with sharp claws act like grappling hooks, anchoring the bird to the bark. Two of the toes face forward and two face backward. The technical word for this arrangement is zygodactyl. This comes from Ancient Greek and means “paired fingers” or “paired toes.” Think about pterodactyl, a word I used earlier. That means “wing-finger.” Zygodactyl feet aren’t unique to woodpeckers. Owls and trogons have them too. But your typical perching birds have three toes forward and one toe backward. That’s called the anisodactyl arrangement.
So our Red-bellied woodpecker is clinging to the bark with its zygodactyl feet. To maintain its perky upright body posture, the bird’s tail also plays an important role. Among birds, woodpeckers have unique tail feathers that are extra stiff. Pressed and spread against the tree trunk, the tail feathers provide a third sturdy point of contact, forming a sort of tripod. Woodpeckers need to brace themselves this way to be efficient in their wood chiseling frenzy.
When the woodpecker is ready to move up the tree trunk, it does a quick little jump. It jumps up a short distance and grabs on again with its feet. These little jumps give the woodpecker’s movements a staccato, stop-motion look when they are hitching themselves up a tree. I love watching woodpeckers moving up a trunk.
Not all members of the woodpecker family Picidae have tails that work this way. I mentioned that the piculets have stubby tail feathers. Piculets belong to their own subfamily which is relatively primitive compared to the true woodpeckers. With their short tails, piculets aren’t as good as bracing themselves and so they spend more time on horizontal branches.
Adaptations for Excavating
When actively looking for prey the Red-bellied Woodpecker is looking for insects and spiders among crevices in the bark. And it’s also listening. Insects like wood boring beetles and their larvae make sounds that the woodpecker can hear.
Reaching a large, dead branch our woodpecker hears some activity inside. It braces itself then begins pecking at the rotting wood. Soon, it’s excavating a sizable hole in the wood and the chips are flying everywhere.
The Red-bellied Woodpecker has a chisel-shaped bill, which is typical for members of the family Picidae. The bill is straight and has a slightly rounded-off or squared tip, making it less likely to be damaged during pecking. As in other birds, the outer layer of the bill is made of keratin. This is the same protein that forms your hair and fingernails. The regular pecking action of the bird helps to automatically sharpen the bill’s keratin sheath.
Once our intrepid woodpecker breaches the insect tunnels in the rotting wood, it uses its long, sticky tongue to snatch its prey. A Red-bellied Woodpecker tongue can extend about three times the length of the bird’s bill. Long tongues like this are the norm for woodpeckers. So chameleons and anteaters aren’t the only animals with crazy long tongues.
But where does this tongue go when the woodpecker isn’t using it? It retracts as part of an anatomical structure called the hyoid apparatus. This structure includes the tongue, the hyoid bones, muscles, and connective tissues. The hyoid apparatus, including the tongue, wraps all the way around the back of the woodpecker’s skull. Imagine your tongue pulling back into your mouth, then behind your head, and then down over your forehead into your eye socket. That’s sort of what happens in woodpeckers.
Hummingbirds, which we talked about in a previous blog article, also have absurdly long tongues and a hyoid apparatus that wraps around the skull.
How the heck do woodpeckers happily whack away at wood without any injuries? This is one of the most amazing things about these birds. Our woodpecker friend has several adaptations that keeps it from knocking itself silly when excavating or drumming on wood. Without these adaptations, it would be at serious risk of getting concussions. A concussion is a brain injury caused by a blow to the head.
The hyoid apparatus is one of these adaptations. Tension in the hyoid apparatus cushions the woodpecker’s skull and diverts vibrations from impacts away from the skull.
Another thing that prevents concussions is the small brain size of woodpeckers. Smaller brain masses are less at the mercy of damaging force. Now, it’s not that woodpeckers have exceptionally small brains. They actually have larger than expected brain sizes, given their body sizes, when compared to most other birds. But birds are small animals, so their brains have small masses in general.
A woodpecker’s skull is reinforced in front and back to withstand repeated blows. And its brain is oriented inside the skull so that there’s a large surface area to absorb any shock. Also, the lower part of the bill, the mandible, tends to strike the wood surface first and this allows the shock to be absorbed by the mandible instead of the cranium. In fact, force tends to be distributed throughout the bird’s body, instead of being concentrated in the skull.
And lastly, compression provided by the tongue allows woodpeckers to maintain blood volume and pressure in their heads. This extra layer of protection acts sort of like blood bubble wrap to protect the brain. Some head-banging mammals like male Bighorn Sheep have similar adaptations to avoid concussions. Biologists have studied woodpeckers and these mammals to figure out how to minimize concussions in football players.
Another occupational hazard for woodpeckers is dealing with sawdust and wood chips. They need to protect their eyes and noses from these particles. Every time a woodpecker strikes wood, it closes its third eyelid, the nictitating membrane. This shields the eye from flying chips. We talked about nictitating membranes in a previous blog article, all about vision in birds.
Many woodpeckers have narrow nostrils and/or protective feathers called nasal tufts to keep woody debris from being snorted. When you consider all of these adaptations you can really appreciate how natural selection has shaped these wonderful birds.
Diet
The Red-bellied Woodpecker is a fine example of a typical species in the subfamily of true woodpeckers. It uses its woodpecking superpowers to find and eat lots of bugs in wood. But its diet is actually much more varied.
Depending on the time of year and on what food is available in the area, Red-bellied Woodpeckers eat all sorts of stuff. More than half of their food can come from plants. Fruit and nuts like acorns and pecans are at the top of the list. Besides beetles, they eat ants, grasshoppers, caterpillars, and other miscellaneous invertebrates.
You might be surprised and perhaps a little horrified to know that this bird also eats lizards, frogs, and nestling birds of many kinds. Yeah, that’s right. Baby birds. Bummer, but so it goes in nature.
This sort of menu isn’t unique to the Red-bellied Woodpecker. The majority of woodpeckers are similarly omnivorous. Take the Great Spotted Woodpecker, for example. This species, which I mentioned is common in Europe and Asia, has a diverse diet. It eats berries, nuts, tree sap, fruit, insects, spiders, mussels, carrion, human food scraps, bird eggs, and yes, baby birds.
Speaking of tree sap, we have some woodpecker species that specialize in eating this sugar-rich liquid. The four sapsucker species in North America all belong to the genus Sphyrapicus. These sapsuckers drill shallow wells into the vascular tissue of living trees. They lap up the sap that oozes out with their brushy tongues. They also eat insects that show up to drink the sap. Many other woodpeckers will eat tree sap, but the sapsuckers have taken this to a whole new level.
Drumming
Drumming in woodpeckers is a distinct behavior. It’s quite different from what they do when they’re foraging for insects in wood. It sounds different and has a totally different function.
Drumming is a form of communication. Because woodpeckers don’t have the fancy vocal abilities of perching birds or other skilled crooners, they can’t use songs to attract mates or intimidate their rivals. Instead, they’ve repurposed their wood chiseling skills to make a sound that accomplishes these same tasks.
While drumming, a woodpecker can strike wood more than 20 times in a second. Most, if not all, woodpeckers use drumming to communicate. Males and females both drum. And this behavior is seasonal, often being limited to the breeding season.
To make the loudest possible drumming sound, a woodpecker will try to find a nice hollow branch or tree trunk. This maximizes the resonance so that the sound will carry a long way. And some clever woodpeckers have figured out that human structures make awesome drums. Have you ever had a woodpecker jackhammering away on your stove pipe or rain gutter? It's super loud.
It’s not so easy to tell woodpecker species apart by their drumming sounds alone. Drumming isn’t as useful as songs to us birders. But there are subtle differences in the rates of drumming that a skilled listener might be able to detect.
Woodpeckers can and do make vocal sounds, even if they can’t sing complex songs. They have calls to keep in contact with mates, to express alarm, and to threaten their enemies.
Recordings of Woodpecker Calls and Drumming
Breeding
Most species are monogamous and have long-term pair bonds. But some will pair up for a single season and then go their separate ways. There are some interesting exceptions to the simple monogamy situation, such as the cooperative breeding of Red-cockaded Woodpeckers and Acorn Woodpeckers. These situations are fascinating and complex, so I’ll come back to them in the future.
All woodpeckers nest in cavities. Most excavate their own nests. But some species, like the Eurasian Wryneck, aren’t able to do that themselves. Wrynecks use either natural cavities or those made by other woodpeckers. And piculets tend to dig out their nests in soft, decaying wood. These little dudes aren’t powerful enough to make cavities in hard or living wood.
Nest cavities don’t need to be in wood, necessarily. Some species routinely dig nests in termite mounds or ant nests. For example, the Rufous Woodpecker in southern and southeastern Asia often excavates its nest in an active nest of tree-dwelling ants.
I already mentioned that a few woodpecker species will nest in holes in the ground. This is useful where trees are scarce. The desert southwest of North America is one such place. But there are some massive, tree-like cactuses, such as the famous saguaro. The Gila Woodpecker and the Gilded Flicker both carve their nests into the wet flesh of these giant cactuses.
Woodpecker eggs are white, just like the eggs of most other cavity nesting birds. When your eggs are hidden in a dark place, there’s no need for them to have pretty colors or camouflage. The male woodpecker usually sits on the eggs at night, alternating shifts with the female.
Baby woodpeckers are born featherless and helpless. We call this type of baby bird altricial. The alternative is precocial, where the newly-hatched bird is ready to rock, with open eyes, functioning legs, and a body covered in warm fuzz.
Both woodpecker parents take care of their helpless babies. The adults return to the nest to regurgitate yummy insects for the nestlings. After about 20 to 30 days, the young woodpeckers are ready to leave the nest.
Ecological Role
Woodpeckers deserve some major appreciation. Not just because they’re funny and charming and beautiful. And not just because they eat insects that might otherwise be harmful to forests.
We need to thank woodpeckers for their important roles as ecosystem engineers. You see, by going about their normal business, woodpeckers unwittingly make changes to their habitats. Some of those changes end up benefiting many other species.
For example, there was a study published in 2004 on cavity nesting animals in British Columbia, Canada. Over 8 years, the researchers collected data from 1,692 cavity nests of birds and mammals in a coniferous forest ecosystem.
It turned out that the Northern Flicker was the most important of the primary cavity excavators. These woodpeckers, the flickers, carved nests into aspen trees and their nests were used secondarily by a whole menagerie of critters.
Birds that used flicker nests included Bufflehead ducks, American Kestrels, Northern Saw-whet Owls, and Mountain Bluebirds. But some mammals also made themselves at home in old flicker nests. These included woodrats, mice, weasels, and squirrels. Sometimes, sadly, flickers get forcefully evicted from their nests by other animals.
The Northern Flickers in that 2004 study were ecosystem engineers that created cavities in the forest. Cavities are a limited and valuable resource. Several other species are also primary excavators in that ecosystem, including Pileated Woodpeckers, Hairy Woodpeckers, and Red-naped Sapsuckers. Without woodpeckers, nest cavities would be in short supply.
Another way that woodpeckers benefit their ecosystems is that they help along the process of breaking down dead wood into soil. When a tree dies, bark beetles, wood-borer beetles, and other insects arrive to eat the wood. They bring with them wood-digesting fungi. Woodpeckers swoop in, tear open the wood and eat the insects. By exposing the wood, the birds increase access for even more insects and fungi. This creates a sort of feedback loop and, eventually, the tree gets recycled into organic soil. This soil will nurture the next generation of trees, insects, and woodpeckers.
Conservation
Out of approximately 240 woodpecker species across the planet, 39 are known to be threatened. The International Union for the Conservation of Nature lists 39 woodpecker species as either near-threatened, vulnerable, endangered, or critically endangered.
Woodpeckers are, by and large, animals of the forest. And forests worldwide are being destroyed at alarming rates. So it's likely that many more woodpeckers will be pushed towards extinction if we don’t protect these habitats. A global analysis published in 2018 indicated that the region with the highest woodpecker diversity is Southeast Asia, where human-modification and destruction of habitat is rampant.
The 39 species that I just mentioned did not include two that are on the IUCN Red List as critically endangered: The Ivory-billed Woodpecker and the Imperial Woodpecker. These birds are most likely already extinct. Gone from the world. There’s a tiny bit of hope that they are still hanging on somewhere. But despite multiple scientific expeditions to find them, no one has seen either species for decades.
The Ivory-billed Woodpecker lived in primeval swamps of the American southeast. Its close relative the Imperial Woodpecker lived in pine forests in the mountains of western Mexico. These were the two largest woodpecker species in the world. Human-caused devastation of their forest habitats has driven them to extinction.
Woodpeckers and Culture
In Sisters, Oregon, (almost) every year the Dean Hale Woodpecker Festival is held in June. This region is a woodpecker diversity hotspot, with 12 species! The festival is fun for the entire family; from the serious bird watcher to anyone that just wants to learn something more about birds. It's A great way to enjoy the beautiful Eastern Cascades of Central Oregon, and learn a thing or two!