'Chimney caps, vent pipes, gutters': Why some woodpeckers are major metal heads

A few weeks ago, at about 6:45 in the morning, I was at home, waiting to talk live on the air with Morning Edition host Michel Martin about a story I'd done, when I suddenly heard a loud metallic hammering. It sounded like a machine was vibrating my house.

It happened again about 15 seconds later. And again after that.

This rhythmic clatter seemed to be coming from my basement utility closet. Was my furnace breaking? Or my water heater? I worried that it might happen while I was on the air.

Luckily, the noise stopped while I spoke with Michel, but restarted later. This time I heard another sound, a warbling or trilling, possibly inside my chimney.

Was there an animal in there? I ran outside, looked up at my roof — and saw a woodpecker drilling away at my metal chimney cap.

I've seen and heard plenty of woodpeckers hammer on trees. But never on metal. So to find out why the bird was doing this, I called an expert: Kevin McGowan, an ornithologist at the Cornell Lab of Ornithology who recently created a course called "The Wonderful World of Woodpeckers."

McGowan said woodpeckers batter wood to find food, make a home, mark territory and attract a mate. But when they bash away at metal, "what the birds are trying to do is make as big a noise as possible," he said, "and a number of these guys have found that — you know what? If you hammer on metal, it's really loud!"

Woodpeckers primarily do this during the springtime breeding season, and their metallic racket has two purposes, "basically summarized as: All other guys stay away, all the girls come to me," McGowan said. "And the bigger the noise, the better."

Over time, some urban woodpeckers have learned that metal is more resonant and reverberant than wood, and amplifies sound much more than trees do, he added.

Woodpeckers that live in rural wooded areas have little access to metal, so "most of them don't get any chance" to exhibit this behavior, McGowan noted, whereas city woodpeckers are surrounded by metal objects of all kinds, "so they're using the best thing in their environment" to trumpet their messages.

Among urban woodpeckers, he added, "not every individual that has the opportunity to peck on metal does it, but some birds do and some apparently like it, and they keep doing it."

The range of metal they'll drum on includes chimney caps, vent pipes, gutters, aluminum siding, TV antennas, drain pipes, satellite dishes and power pole transformers, according to Brian Smith, assistant regional director of the migratory bird program for the U.S. Fish and Wildlife Service's Midwest region.

"When people and wildlife start to intertwine where they live, there are going to be things that pop up, like this," Smith added.

Smith said he knows of a woodpecker that drilled on a metal water heater vent, producing "a very, very loud booming sound across the neighborhood," and another that flew from house to house to house, hammering away at gutters and chimney caps so loudly that "I could hear him about ten houses away."

"It can be pretty alarming, like, what in the world is that?" said Smith. "And, boy, if they can make it louder, they sure will."

The Cornell Lab of Ornithology's Macaulay Library has an audio collection of woodpeckers hammering at metal, including a traffic sign, a ladder, a roof and a windmill.

Is there a way to stop this behavior? Yes, but there's a legal catch: "Because they're migratory, they're protected, so if you wanted to remove the bird itself, you'd have to get a special permit," explained Dan Master, owner of Critter Control of Greater Boston, which sometimes responds to calls about nuisance woodpeckers.

Specifically, woodpeckers are covered by the Migratory Bird Treaty Act, so capturing them requires federal permission. But people are allowed to scare them off with noise deterrents, like a recording of a screeching hawk, or physical deterrents, such as windsocks, pinwheels and balloons.

Master said his company typically uses "simple mylar ribbons" to shoo away woodpeckers. "They're red on one side and silver-shiny on the other," he said, "and [birds] don't like the way they move and make a little bit of noise when they flap in the wind."

Woodpeckers can put dents in gutters and aluminum siding, but they're unlikely to do as much damage to metal as they can to wood siding. Still, when they hammer on metal, especially on someone's house, that can initially create confusion about what's causing the noise.

"One homeowner called and said it sounded like there was jackhammering going on in their fireplace," Master recalled. "When we hear those descriptions, we know it's the woodpecker."