Home & Garden Columns

Do Woodpeckers Get Headaches? If Not, Why Not?

By Joe Eaton, Special to the Planet
Tuesday November 21, 2006

You may have noticed last month that the Ig Nobel laureates for 2006 included Ivan Schwab, a professor of ophthalmology at UC Davis, recognized for his explanation of why woodpeckers don’t get headaches. 

The Ig Nobels are bestowed for the year’s most dubious contributions to science (and sometimes other fields: last year’s literature prize went to the collective authors of the Nigerian Prisoner Scam email and all its variations). 

Other winners included studies of why the sound of fingernails scraping on a blackboard is irritating, why dry spaghetti breaks into multiple fragments when you bend it, and whether mosquitoes are more attracted to human feet or Limburger cheese. In previous years, research on how herring communicate by farting and the fluid dynamics of swimming in syrup has been honored.  

Schwab, who accepted the award wearing a red-crested, beaked headdress and a tux, was actually piggybacking on the work of the late Philip May of UCLA. 

May’s articles on the anatomy and physiology of the pileated woodpecker had appeared in scholarly journals like The Lancet; Schwab just summarized May’s findings in his monthly column for the British Journal of Ophthalmology, in which he has covered such topics as how kingfishers spot fish underwater and why the eyes of goats have slit pupils.  

So why don’t woodpeckers get headaches? By all rights they should, considering the beating their heads take. May calculated that a pileated woodpecker, which is about crow-sized, may strike a tree trunk at a rate up to 20 times a second up to 12,000 times a day, with a 1200 g force on each impact. This would be roughly equivalent to hitting a wall face first at 16 miles an hour. Few of us could take 12,000 repetitions of that sort of thing. 

But then we’re not built like woodpeckers. The bird has a thick skull with spongy cartilage at the base of its beak to absorb the force of all that hammering. The mandibles—the upper and lower jaws—are attached to the skull by strong muscles that contract a millisecond before each blow, creating further cushioning. 

The muscles also divert the force of the impact to the base and rear of the skull, bypassing the brain. 

Each hammer blow is a perfect perpendicular stroke, without the torsion that might tear the membrane enclosing the brain or cause concussion. 

A pileated woodpecker also has a relatively small brain for a bird its size. The small ratio of brain weight to brain surface area allows the force of an impact to spread over a larger area, further reducing the risk of concussion. 

I don’t know whether the small-brain principle also holds for the smaller woodpeckers—the downy, the hairy, the acorn, the Nuttall’s—which are also dedicated headbangers.  

According to Schwab, high-speed photography of a woodpecker in action shows that the bird closes the nictitating membrane—the so-called “third eyelid”—over each eye in those pre-strike milliseconds. 

He speculates that this may serve to restrain the eyes from literally popping out of the woodpecker’s head, in addition to providing protection from flying debris. In addition, the pecten, a ridged portion of the eyelid, fills with blood to increase pressure on the lens and retina during the strike, apparently preventing retinal detachment. 

Then there’s the tongue. It’s not clear whether this extraordinary organ acts as a supplemental shock absorber, but clearly Schwab could not resist describing it: “The tongue is most unusual as it originates on the dorsum of the maxilla, passes through the right nostril, between the eyes, divides in two, arches over the superior portion of the skull and around the occiput passing on either side of the neck, coming forward through the lower mandible, and uniting into a single tongue in the oropharyngeal cavity.” Sorry about the anatomical Latin. 

“Through the right nostril” is my favorite part of the tongue’s itinerary, and I would like to hear some advocate of Intelligent Design venture an explanation of all this.  

What this Rube Goldbergian anatomy does is allow the woodpecker to extend its tongue up to 4 inches beyond the tip of its bill (and remember, we’re dealing with a crow-sized bird). This enables it to get at insects lurking deep under the bark of trees. 

The tip of the tongue is further equipped with sticky saliva to which ants adhere and backward-pointing barbs for impaling beetle grubs and other larger insects.  

All well enough, but it appears to me that the question of woodpecker headaches remains open. 

A headache is a subjective kind of thing, and I’m not sure—barring brain scans on an active woodpecker—we can know for certain whether the birds suffer headaches as an occupational hazard or not. It’s up to some enterprising graduate student to pick up the torch from Dr. May.