Pileated Pair

The Pileated Woodpeckers are just so striking to see (pun intended), and you know there are big old trees nearby somewhere whenever you see them.  There is a pair that lives on the hill above our house.  We can hear them calling during the spring and summer, and occasionally they come down to feed on the bugs happily eating our sickly oak tree (SODS strikes again).   Although I have heard the pair calling back and forth, I've never seen them together, until yesterday.  A second one flew into the frame while I was filming the first excavating.  You can hear them briefly greet each other, before they move to the opposite side of the tree, and one flies away.  A pair defends its territory year-round, so I imagine these are the same ones I often hear, and a pair member will not abandon a territory even if its mate is lost.

The Pileated Woodpecker is the largest woodpecker in most of North America, nearly as large as a crow with a large, dull black body and red crest. If you see one, you will immediately know it is something different than other local woodpeckers.  Its loud ringing calls and huge, rectangular excavations in snags indicate it’s presence in forests across the continent.  Only large-diameter trees have enough girth to contain nest and roost cavities of the large Pileated Woodpecker, so there is concern for populations of this woodpecker where old-growth forests are being converted to younger stands. Availability of suitable habitat is apparently the factor limiting most populations. In young forests, it will use any large trees remaining from before the forest was cut. Because these trees are larger than the rest of the forest, they present a lightning hazard to the nesting birds. 

The Pileated Woodpecker gleans insects (primarily carpenter ants and wood-boring beetle larvae) from branches, trunks, and logs, although it will also eat  fruits, and nuts. Because of its size and strong chisel-shaped bill, this woodpecker is particularly adept at excavating, and it uses this ability to construct nest and roost cavities and to find food. The pilieated woodpecker makes deep rectangular excavations in trees and logs in pursuit of insects.  These excavations can be so broad and deep that they can cause small trees to break in half. It will also pry off long slivers of wood to expose ants. 

Most woodpeckers also drum on objects as a form of communication and territory defense. When doing so, they try to make as loud a noise as possible, and that’s why woodpeckers sometimes drum on metal objects. One Northern Flicker in Wyoming could be heard drumming on an abandoned tractor from a half-mile away!

In its excavating, this species plays a crucial role in many forest ecosystems in North America; a diverse array of other birds—as well as mammals, reptiles, amphibians, and invertebrates—use its cavities for shelter and nesting.  The feeding excavations of a Pileated Woodpecker are so extensive that they often attract other birds. Other woodpeckers, such as the Hairy Woodpecker, as well as House Wrens, may come and feed there.

Woodpecker species have some really amazing evolutionary adaptations for their way of life.  Their skull structure, beak, tongue, tail, and even toes have special adaptations for drilling into wood.  Although each species of woodpecker is unique, and all vary in their particular adaptations, there are some general trends among the group that are impressive.

-      Skull/Brain:  If any of us tried to bang our head against a tree even once, much less at the force and frequency of the woodpecker, we’d have quite a headache (not to mention significant brain damage).  However, the woodpecker’s skull is specially designed to withstand repeated blows and to protect the bird’s brain from concussion. Woodpeckers are capable of repeated pecking on a tree at remarkably high decelerations (stopping time, also a measure of force) on the order of 10 000 m s−2 or 1000 g.  There are three keys to woodpeckers' ability to withstand high decelerations: their small size, which reduces the stress on the brain for a given acceleration; the short duration of the impact, which increases the tolerable acceleration; and the orientation of the brain within the skull, which increases the area of contact between the brain and the skull.  Also, unlike other birds, the bones between the beak and the skull are joined by a flexible cartilage, which cushions the shock of each blow. 

-      Toes and Tail: To generate that much force, the woodpecker has to actually be firmly attached to the surface it is drilling into.  If it wasn’t, it would just knock itself off the tree after the first blow.  Woodpeckers have a special toe arrangement that helps give them the solid base they need.  This is arrangement is called “zygodactyl feet”, and consists of four toes, the first and the fourth facing frontward and the second and third facing back, attached to sharp claws and short-strong legs.  This arrangement is good for grasping, as well as walking vertically up a tree trunk.  The tails of all woodpeckers are stiffened, and when the bird perches on vertical surfaces, the tail and feet work together to support it.  Its sharp claws dig into the wood, and its stiff, square tail feathers braced against the tree act as a support prop.

-      Beak: Woodpeckers are noted for their stout, chisel-like beaks which they use to drill holes in trees to obtain food, make a nest/roost cavity, or territorial drumming.  Species of woodpecker and flicker that use their bills in soil or for probing as opposed to regular hammering tend to have longer and more decurved bills.

-      Tongue: After drilling a small hole with its beak, many woodpeckers, then use their narrow, probing tongue to dislodge and extract insects from their burrows in the wood or bark. The long sticky tongues, which possess bristles, aid these birds in grabbing and extracting insects deep within a hole of a tree. Some woodpeckers can even extend its tongue four to five inches beyond the tip of the beak to access hidden goodies such as insects deep in the bark. 

-      Eyes and Nose: The millisecond before contact with wood a thickened third eyelid (“nictitans membrane”) closes, protecting the eye from flying debris. The nostrils are also often protected by only having a slit-like opening, with special feathers to cover them.

I admittedly have a soft spot for these gigantic woodpeckers.  And luckily, that soft spot is in the cambium of our old oak.  

References:

Cornell Lab of Ornithology - http://www.allaboutbirds.org/

Cornell Lab of Ornithology - The Birds of North America Online (A. Poole, Ed.). Ithaca: Cornell Lab of Ornithology; Retrieved from the Birds of North America Online:http://bna.birds.cornell.edu/bna/species/

Gibson L. (2006) "Woodpecker pecking: how woodpeckers avoid brain injury" Journal of Zoology 270: 462–465 doi:10.1111/j.1469-7998.2006.00166.x

Short, Lester L. (1979). "Burdens of the Picid Hole-Excavating Habit". Wilson Bulletin 91 (1): 16–28. http://elibrary.unm.edu/sora/Wilson/v091n01/p0016-p0028.pdf.
http://www.friendsofcortemaderacreek.org/cn/WoodpeckersoftheWatershed.pdf