"Woodpecker," we think, when we see a black and white bird at our feeder or on a tree trunk, lumping members of a diverse family together. But which one is it?

Woodpeckers deserve a second look, because there's more to these interesting birds than initially meets the eye. For one thing, they show a great deal of variation in size, with tiny downy woodpeckers dwarfed by the other species, especially their big cousins, the pileateds. We associate woodpeckers with trees, but one, the Northern flicker, really prefers to forage on the ground, for ants and other insects.

Most do spend the bulk of their time in trees, but use different pecking styles to forage, dictated by the size of their beaks, from the small pick of a downy to the massive chisel of a pileated.

Even in winter, this family of birds is mainly focused on insects, which make up three-fourths of their diet. They hunt the trees in their territory over and over so assiduously that it's a wonder there are any insects left to emerge in the spring. The small woodpeckers poke and peek into bark crevices, while the mid-sizers, the hairy and red-bellied, drill past the bark to find insect larvae. Pileateds use their large, powerful beaks to reveal galleries full of plump carpenter ants, leaving behind large holes.

Which brings us to a major question people often have about woodpeckers: Do they kill trees?

And the answer is no; woodpeckers rarely, if ever, do significant harm to healthy trees. If woodpeckers are chipping into a tree, it almost certainly is already diseased or damaged, which draws insects, which, in turn, attract the woodpeckers.

"Woodpeckers are part of the natural function of the forest and excavate cavities to extract insects in dead or dying trees," says Lee Frelich, director of the University of Minnesota's Center for Forest Ecology.

They also excavate holes in trees in springtime to hold their offspring, and then, when the youngsters fledge, the family leaves and the hole goes up for grabs. Any one of the many residents of the forest will then claim the space, from gray, red or flying squirrels to cavity-nesting birds like Eastern bluebirds, great-crested flycatchers, chickadees or small owls, like saw-whets or screeches.

If your home has a wood exterior, you may feel differently about woodpeckers than do those of us whose homes are brick, stucco or vinyl-sided (see box for deterrence sources).

Here are bios of the most common tree-pecking birds you might see at your feeders this winter:

Downy woodpecker

Size: 6½ inches long, our smallest woodpecker, females bigger than males.

Range: Found nearly everywhere in U.S. and Canada, year-round.

Habits and habitat: The woodpecker most likely to visit feeders. Not shy, allows close approach. Bark forager, eats insects, berries, fruit, nuts, seeds, suet.

Markings: Only males have a red patch on the back of their head.

Call: Makes "pik" call or whinnies like a little horse.

—

Hairy woodpecker

Size: 9½ inches long, females bigger than males.

Range: Found nearly everywhere in U.S. and Canada, year-round.

Habits and habitat: Attracted to suet and peanut feeders. Quite shy, easily startled into flight. Drills into trees to find insects.

Markings: Only males have a red patch on the back of their head.

Call: Similar sounds to downies, but lower-pitched.

—

Red-bellied woodpecker

Size: 9½ inches long, both genders about the same size.

Range: Found in eastern half of U.S.

Habits and habitat: Will visit suet and peanut feeders. Shy, easily startled. Checks bark, drills into trees for insects.

Markings: Males have red-orange patch from nape to beak, females only on nape.

Call: Makes "cha" call and rolling "churr" sound.

—

Pileated woodpecker

Size: 16 ½ inches long, crow-sized, Minnesota's largest woodpecker.

Range: Found in eastern half of U.S., Pacific Northwest.

Habits and habitat: A woodland bird, sometimes found at suet feeders. Very nervy, easily startled. Excavates deep holes in fallen trees in search of carpenter ants.

Markings: Males have red cap and mustache, females show smaller red cap.

Call: Call is a daffy "wuck" sound (think Woody Woodpecker).

—

Another three:

Northern flicker

Size: 12 ½ inches, males have black mustache.

Range: Many in our area shift south for the winter.

Diet: Attracted to suet and peanuts.

—

Yellow-bellied sapsucker

Size: 8 ½ inches, red forehead, yellow belly.

Range: Migratory, will return in spring.

Diet: Drills into trees for sap to drink.

—

Red-headed woodpecker

Size: 9 ¼ inches, both have red head, white belly.

Range: Uncommon in our area, habitat specialists.

Diet: Seldom seen at feeders, population in decline.

—

Deterring woodpeckers

Woodpeckers don't differentiate between trees and wood exteriors, and may create holes in siding and trim, which can create frustration among homeowners. Downy woodpeckers are usually the culprits, maybe partially due to the fact that they're our most abundant woodpecker.

It takes a concerted effort to stop them from drilling into your siding, and it's worth trying a variety of techniques. There are excellent tips for deterring woodpeckers at the Cornell Lab of Ornithology site birds.cornell.edu/wp_about.

Another good source is the Minnesota DNR's site: dnr.state.mn.us/livingwith_wildlife/woodpeckers/index.html.

This site points out that no one method works in every case, so try a variety of possible solutions.

—

Millions of woodpeckers

Woodpecker populations in U.S. and Canada according to Partners in Flight:

Downy woodpecker 13 million

Hairy woodpecker 8-9 million

Red-bellied woodpecker 16 million

Pileated woodpecker 2.6 million

Northern flicker 11 million

Yellow-bellied sapsucker 14 million

Red-headed woodpecker 1.8 million

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