A walk in the forest, even an urban forest, sometimes reveals the strange sight of a tree that looks as if it had been bombed. Long shards of broken bark lie scattered around a trunk marked by large, deep holes.

This is the handiwork of Minnesota's largest woodpecker, the pileated, whose huge chisel beak can dramatically alter a tree. This woodpecker drills into the trunk of a dead or dying tree in search of its favorite meal, a nice, gooey ball of carpenter ants.

They're impressive birds, nearly twice as large as backyard woodpeckers such as red-bellied and hairy woodpeckers. Most of us are familiar with Minnesota's smallest woodpecker, the downy: Stack three downies, one on top of the other, and you'll have a sense for the pileated's size.

"A magnificent bird, nearly the size of a crow and nearly as black, but adorned with a flaming red crest and showing, in flight, great white patches in the wings," aptly wrote Thomas Sadler Roberts, ornithologist and first director of the Bell Museum of Natural History, in a work published in 1934.

A startled response is everyone's inevitable reaction to a first sighting of these big boys of the forest.

They fly through the woods leading with that massive beak and with long wings outstretched, creating the illusion of an even larger bird. Then they fold their wings and gracefully land on a tree trunk, and all but disappear. But wait patiently for a minute and you'll often spy the bird hitching its way upward, tapping and listening for the sounds of insects chewing away under the bark.

A 'bug bird'

Like all woodpeckers, its diet is largely made up of insects, primarily ants and wood-boring beetle larvae, small prey for such a big bird. Finding a tree chamber filled with busy carpenter ants really makes a pileated's day, and it eagerly flicks its long, sticky tongue inside to pull out balls of squirming insects.

"They're so enthusiastic about finding an ant meal that you almost feel like jumping in there to join them," a friend once joked.

We expect to see large birds up near the tops of trees, so it's often surprising to discover a pileated pecking away down near the base, or on a stump or fallen log. They favor really big trees for carving out nesting and sleeping quarters, so large stands of forest are their favorite habitat. But they can be found in suburban settings and even city parks.

I once watched a pileated on a December day flying from shrub to shrub at a friend's suburban home, pecking at each bulb in a strand of holiday lights. The red bulbs must have resembled berries to the bird, another important element of its diet.

They're big fans of suet, a food that approximates the high-energy calories found in grubs and ants, so backyards that offer suet baskets can sometimes pull in pileated woodpeckers.

A zany side

They have a wacky call, a single "wuck" note or a series of them, and another bird watcher said they have a zany side, as well. She described a pileated that lived in the woods near her parents' cabin flying in to stare in the window at her mother while she lay ill. The bird would peck at the cabin walls or door frame, once even ringing the doorbell by accident.

Despite being so large, pileated woodpeckers can often pass unnoticed, unless they're calling to a mate or drumming to maintain a territory. One way to find these secretive birds is to follow the sound of very loud knocking resounding through a forest. I've never been lucky enough to catch a pileated in the act of carving off bark in search of an ant meal, with wood chips flying in all directions, but I've got hope.

The holes they make in search of insects penetrate deep into a tree, but these pale in comparison to the 2-foot deep holes pileated woodpeckers chisel out to serve as nesting or sleeping quarters.

It's these latter holes that are so important to many other forest creatures, so much so that pileateds are called a "keystone species," playing a key role in the survival of other living things. After the woodpecker family leaves its nest cavity in midsummer, the hole becomes available to wood ducks or screech owls, martens, hooded and common mergansers, bats, fishers, flying squirrels and even gray squirrels to use as their own nesting and/or sleeping quarters.

Sometimes these shy woodpeckers are silent and stealthy, and sometimes the forest rings with their goofy calls, but a sighting of a pileated woodpecker brings a bit of magic to any tromp in the woods.

A few facts

• That giant chisel beak never wears down because its cells are constantly being replaced.

• The skull acts as a shock absorber so heavy drilling doesn't damage their brain.

• Bristly feathers over the nostrils keep out wood particles.

• Both the male and female incubate their eggs, splitting the daylight hours while the male takes the night shift.

• If a pileated woodpecker is attacking your wood siding, it's almost always a signal that carpenter ants have invaded.

St. Paul resident Val Cunningham, who volunteers with the St. Paul Audubon Society and writes about nature for local, regional and national newspapers and magazines, can be reached at valwrites@comcast.net.