Why don’t woodpeckers get concussions?

A female Pileated Woodpecker has been excavating many large holes on a neighbor’s tree.  At first I thought (and hoped) she was excavating a cavity for a nest, but no such luck.

female Pileated Woodpecker-1

The female Pileated has a black whisker stripe behind the bill, while the male’s is red.  She has been a regular visitor to this tree for most of a week, and has enlarged the excavation noticeably each visit.

From the extent of damage along the length of one of the trunks of the tree, it seems more likely that she is just digging for insects, and these particular insects live pretty deep in the tree and are spread out in many pockets of the wood.

female Pileated Woodpecker-

She has worked her way down the trunk about 6 feet. Other woodpecker species have also checked out her work and drilled a few of their own holes in this long stripe.

If you haven’t watched a Pileated Woodpecker go about their excavation, it bears some description.  They open up a wide cavity by judicious pecks with their chisel-shaped bill at just the right angle to flake off large chunks of wood.  Hit it from the right and down, then from the left and down, repeat once or twice, and a big wood chip goes flying.  The pile accumulating at the bottom of the tree grows each day the woodpecker visits (always the female), and she works at it for 1-2 hours at a time.

female Pileated Woodpecker-

She closes the nictitating membranes (white covering) over her eyes just as her head makes contact with the wood.

Every now and then she stops, looks into the hole, flicks out her tongue and snags some hapless crawling thing, and then continues the destruction.

female Pileated Woodpecker-

Her tongue protrudes from the tip of her beak as she probes into the most recent patches of her digging.

female Pileated Woodpecker-

She seems to have uncovered a whitish cylindrical mass, perhaps a larva buried deep in this wood.

She hammers away for extended periods of time with an acceleration force of 1000 x g  — an impressive feat when you consider that humans can withstand no more than about a 100 x g acceleration.  So, how do woodpeckers avoid getting concussions from all that hammering?  It turns out they have multiple safeguards against injury from chiseling wood.

  • First, it should be noted that woodpeckers typically excavate rotting wood, which tends to be softer after decomposing fungi have been at work. The beak penetrates the wood, rather than stopping at the surface with collision impact.
  • Second, woodpeckers strike the wood at an angle, giving it a glancing blow, and the beak makes contact for just micro-seconds, which lessens the impact. Because bottom bony part of the beak extend further than the upper part, the brunt of the blow is transferred to the lower part of the bill which is not connected to the braincase.
  • Third, woodpeckers have unusual skull anatomy that acts like a shock absorber, with elongated (hyoid) bones and muscles that support the tongue wrapped around the back and top of the skull.  Cranial bone of woodpeckers is spongey and composed of plates that slide over one another to absorb the force of a beak strike.
Flicker-Tongue-from birdwatchingdaily.com/blog

A diagram of the Flicker’s very long tongue shows how the tongue support (hyoid bones) curves from below the beak around the back and top of the skull.  Not only do the hyoid bones and muscles act like shock absorbers for the skull, but the spongey nature of cranial bone with diffuse air pockets embedded in the bony layers helps absorb the impact of the blows.  Birdwatchingdaily.com/blog — 12/10/13

  • Fourth, and importantly, reduced fluid cavities in the woodpecker brain mean it does not slosh around in the cranial cavity as the human brain does upon impact with an immovable object.  It is the impact of brain tissue with cranial bone that causes concussions in humans.  With the woodpecker brain tightly encased in spongey bone and restrained with hyoid muscles and bone as a seatbelt, the brain is well-protected from concussive forces.
woodpecker helmet

The woodpecker helmet — Toronto Star sports page, Oct. 27, 2011.

It’s amazing what we can learn from the “lessons of nature”.  With what we now know about woodpecker skull anatomy, perhaps sports helmets of the future may incorporate some of the features that protect bird brains from concussion.

ah, spring!

Our weatherman has reported the end of winter here in MN; mild weather lies ahead in the forecast.  I haven’t worn a coat outside for the past two days — ah, spring!

While we rejoice in the pleasant weather, springtime isn’t a cakewalk for the wildlife. Yes, temperatures are more tolerable, but increased daylength in the spring usually means animals are more active (thus, increasing energy expenses) and there is even less food for them than there was a couple of months ago.   The vegetation is still dormant, as are the insects, and flowers, fruits, and nectar won’t be available for weeks.  So…it’s back to the bird feeders to supplement the waning nutrition found in the forest.

Pileated Woodpeckrr male

That huge bill makes big gouges in the peanut butter suet, as this male Pileated Woodpecker takes a big bite.

Pileated Woodpeckrr male

Males have a red mustache, an all red feather crest, and black breast and belly feathers.

I’ve often heard the Pileated Woodpeckers make their eerie-sounding call in distant backyard.  The pair is resident on the same territory all year, though it might expand slightly in the winter.  But the first time I’ve seen them at the suet feeders this winter was just the past week, so perhaps supplies of overwintering grubs is running low in the forest.

Pileated Woodpeckrr female-

Mrs. Pileated prefers the suet stacks in the seed feeder. She seems to have lighter-colored breast and belly feathers.  Her mustache is black, and the red head feathers do not extend down to her beak, as it does in the male.

Pileated Woodpecker female-

She, too, bites large chunks of the suet and gulps them down before flying off, back to the forest.

Pileated times two

It’s a great day when I get to see our largest woodpecker, the Pileated, in the open and can get organized quickly enough to get some photos of the bird.  It’s an even greater experience to see a pair of them pose for me close enough to hardly even need the telephoto lens.

a pair of pileated woodpeckers

The pair played ring around the Buckeye tree for a few minutes, usually with just one of them in view at a time.  Notice how they have their red crests somewhat erected — more on that later. (Taken through the window, so somewhat blurry)

These birds are truly impressive, almost as large as a crow in body size, with a striking black and white pattern, a flaming red crest, and an impressive chisel at the end of their long beak.  I wouldn’t want to try to take one of these guys out of a bird net!

The pair stay together all year on their territory, though its size or shape may change in area seasonally, as they expand it in search of food in the winter.  Although I have heard them calling out in the wetland and occasionally seen one of them flying around, I’ve never seen them together, and here they both were at the suet feeders.

pileated woodpecker female

The female Pileated Woodpecker sports a black mustache, which makes her easy to tell from the red-mustachioed male. Note:  in comparison to this large-bodied bird, a Downy Woodpecker’s body length would stretch only from one suet plug to the next.

pileated woodpecker male

Such a handsome guy! Unlike the little Yellow-bellied Sapsucker who dines for minutes at a time, the Pileateds ate very little of the suet before moving on.

Even though this is a mated pair, their harmony seems to depend on an established social hierarchy — i.e., whoever gets to the food first owns it, no sharing.  It could be that males are a little more possessive about this, but I didn’t observe whether the female would defend her own feeder from him in a similar manner.

pileated woodpeckers

While the male was feeding at this suet feeder, the female came over and perched nearby.  She might have thought this one had better suet than the one she had just left?  But in response he raised his crest feathers, and then so did she.

pileated woodpeckers

Then she tried to land on the other side of the feeder log, and that didn’t go over well with him at all. Notice those red crest feathers standing out from the back of his head.

pileated woodpeckers

Threat over, he goes back to feeding, and she pretends to hide behind a branch, crest feathers relaxed.

So, if you have to compete with your mate for food, then what’s the advantage of staying together during a time when food is so limited in the winter?  To protect the area from other Pileated Woodpeckers that might want to establish a breeding territory there?  To get a jump start on the breeding season, without having to spend time and energy looking around for prospective nest holes?  Perhaps these advantages outweigh the disadvantage of competition for food, or perhaps there really is no competition because the male and female forage in different ways that nets success for both.

Spring cleaning

Walking along the Mississippi River among the trees of the flood plain forest this morning, I heard a deep, resonant drumming that could only come from one bird, so I followed the noise and found…

a beautiful male Pileated Woodpecker drumming at the top of a 60 foot dead tree.

a beautiful male Pileated Woodpecker drumming at the top of a 60 foot dead tree.

After a succession of drumming solos, he disappeared around the back side of the tree, so I followed and got closer.

Aha!  He was working on a nest cavity.

Aha!  He was working on a nest cavity.  (The male’s mustache is red; the female’s is black, so we know this is Mr. Pileated).

The male and female Pileated pair stay together on their territory in mature forest all year, but almost always construct a new nest each  year.  These abandoned nest holes are highly sought after by other bird or mammal species to raise their own broods.

The male starts the nest construction process and the female completes it, but the whole process takes 3-6 weeks.  Apparently in this part of the construction phase, there was quite a lot of debris that required clearing out, before he could enlarge the hole or excavate any further.  Eventually the nest hole will be 10-24 inches deep.

pileated woodpecker-male excavating nest cavity-3

He kept this up for several minutes, throwing out some pretty hefty chunks of wood.

He kept this up for several minutes, throwing out some pretty hefty chunks of wood.

Then he emerged and climbed out of the hole, although not very gracefully.

Then he emerged and climbed out of the hole, although not very gracefully.

It's not easy getting out of a little hole and finding something on which to cling while getting upright again.

It’s not easy getting out of a little hole and finding something on which to cling while getting upright again.

Inspecting the entrance again, deciding whether to go drumming again...

Inspecting the entrance again, deciding whether to go drumming again…

Pileated Woodpeckers are a kind of keystone species in these mature forests, that is, a species on which many other species depend.  Their excavations open up resources for a variety of other animals, both for food and for nesting sites.  Flying squirrels, red and gray squirrels, owls, tree-nesting ducks, and a variety of small songbirds make use of the (con) and (de)structive work of Pileated Woodpeckers.

Bird-watchers

What are you boys looking at?

What are you boys looking at?  Jack says, “look there’s a bird on that tree”.

The recent storms have left many downed trees and broken branches on the ground.  The up-side of all the broken tree limbs is that it exposes potential foraging sites for woodpeckers, like this female Pileated Woodpecker in Alison’s backyard.  (All photos courtesy of co-blogger Alison).

_MG_3025 copy

_MG_3023 copy

There's something good in here!

There’s something good in here!

Got it!

Got it!

A rare sighting

It’s rare for me to see one Pileated Woodpecker, let alone two Pileateds at once.  But when you do see two woodpeckers together at this time of year, you might be lucky enough to see this!

Mr. Pileated cautiously approaches his lady love.

Mr. Pileated cautiously approaches his lady love.

No foreplay here, just let me jump on your back.

No foreplay here, the male just jumps on her back.  The male sports a red mustache; the female’s facial stripe is black.

The all-iimportant transfer of sperm might have taken as much as 2 seconds.

The all-important transfer of sperm might have taken as much as 2 seconds.

Now this female can go lay her eggs in the nest hole she and her mate excavated in a nearby snag.

Now this female can go lay her eggs in the nest hole she and her mate excavated in a nearby snag.

The Pileated Woodpecker pair stays together all year, defending a territory in a particular area containing suitable dead wood.  They create new nest holes each year, leaving the old ones for other tree-nesting species.  Sometimes their excavations are so large and so vigorous they actually topple the top of the snag right off.

Small, medium, and really big — Woodpeckers

Three species of woodpeckers at the suet feeders in one day!

I managed to trim the photos of the Downy and Hairy Woodpeckers to the same relative magnification using the suet feeder as a guide, so you can see the size difference between them. (Click on the image below for max resolution)

Downy Woodpeckers (left) weigh 20-30 grams and are 5-7 inches long, while Hairy Woodpeckers (right) weigh 40-90 grams and are 7-10 inches long.  These particular birds are both females — there might be larger differences between males of the two species.

Downy and Hairy Woodpeckers are common and inhabit the same range over most of North America, where both species are year-round residents.  They compete for nest sites, as well as food, in mature forest, and can be aggressive toward one another.  Although they seem to have identical plumage as adults, Downy and Hairy Woodpeckers are actually not very closely related genetically.  It is thought that the two species have converged on a single black and white plumage pattern, maximizing their ability to recognize each other and defend feeding and nesting territories from each other (interspecific territoriality).

And then, there’s this guy, a handsome male Pileated Woodpecker, whose head and neck are about the same length as the little Downy.

This might be one of the pair of Pileateds I keep hearing back in the woods, but have never seen.  Our subfreezing night time temperatures have made the suet feeders quite attractive to all sorts of birds, even these mammoth wood chippers.  He doesn’t have the right body shape to utilize this tiny feeder, though.

Pileated Woodpecker prize

Success!  At last I found a Pileated Woodpecker that sat still long enough for me to photograph.

Tap,thunk, bonk, just like a hammer on a hollow log — that’s what a pileated woodpecker sounds like when it is chipping away dead wood in its search for food.  I heard the bird but couldn’t find it, until I finally caught just a flash of red in the sea of brown bark.

This bird visited every broken branch in a group of large, mature oaks for about 15 minutes, but it was impossible to get a clear shot of it with all the spiny buckthorn undergrowth in the way.  Why are there always branches between me and my subject?

Compared to the rat-a-tat of downy woodpeckers, this bird’s bill operated in slow motion.  But each strike was a measured blow, like a chisel, and when that bill hit the dead wood, the chips did fly — out of the hole, onto the bird, etc.  In several of my photos, I noticed the bird pulled its nictitating membrane (thin skin located between eyelid and cornea/sclera) over the eye, making it look gray.  I assume this is for protection from flying wood particles.

I think this is a female; she has black instead of red feathers above the beak (forehead area), and she has a black chin stripe instead of a red one, as in the male.

Their body size is impressive, as are the large feet with strong toes and long nails.  All woodpeckers have two forward and two backward pointing toes which enable them to perch on vertical surfaces.  Short, stiff tail feathers offer additional support as a prop against the tree.

After the woodpecker finished excavating, chickadees came by to check out the hole and see what the woodpecker might have exposed for them to eat.

Pileated Woodpeckers are year-round residents throughout their range, and seem quite adaptable to a variety of forest types, including suburban trees.  Like northern flickers, they may specialize on ants, excavating their galleries deep in the wood and then lapping them up with their long tongues.  But when insects are in short supply, they eat fruits, nuts, berries (including poison ivy berries), and even seed from bird feeders.  I’ve seen them at my feeders already this winter and will keep looking for the perfect photo op (i.e., bird without branches.