Ash borer invasion good for woodpeckers, nuthatches, both natural insect predators

| Thursday, Aug. 15, 2013, 9:40 p.m.

In the bug-eat-wood world that is ridding the country of its ash trees, scientists have learned that some bird species are thriving by feasting on the invaders.

The populations of red-bellied woodpeckers and white-breasted nuthatches, both natural insect predators, soared in the Detroit area, ground zero of the emerald ash borer invasion, research by Cornell University and the U.S. Forest Service found.

Scientists discovered the destructive beetle's presence in southeastern Michigan in 2002. Five years later, the voracious green beetle arrived in Cranberry.

“It's pretty horrific, really,” said Andrew Liebhold, an entomologist with the Forest Service in Morgantown, W.Va., and co-author of the study. “In the Pittsburgh metro area, it is about 10 to 15 years behind Detroit. The worst is yet to come.”

The region's woodpecker and nuthatch populations could surge, he said.

“It's probably affecting a whole slew of other organisms, but people count birds, so we can track it,” Liebhold said. “People don't really count the number of millipedes in their backyard.”

While researchers focused on the Detroit area, Pittsburgh served as one of five control sites across the Midwest.

In addition to gains in the numbers of the red-bellied woodpecker and white-breasted nuthatch, downy and hairy woodpecker species initially saw population declines after the emerald ash borer's appearance but have rebounded in recent years.

All four bird species noted in the study live in Western Pennsylvania.

The impact woodpeckers have had on ash trees in city parks caught Phil Gruszka's attention. He's director of parks management and maintenance policies for the Pittsburgh Parks Conservancy.

“We can tell there are more woodpeckers in the parks,” he said. “You see the bark off all the trees.”

Signs of an ash tree infested with emerald ash borers are stripped bark and woodpecker markings, Gruszka said.

Pittsburgh's public parks contain about 60,000 ash trees. Pennsylvania is home to 300 million, according to the state Department of Conservation and Natural Resources.

The emerald ash borer will kill nearly all of them, as North American ash trees have no natural resistance to the insects.

“But the tree species isn't going to go extinct,” Liebhold said.

Emerald ash borer larvae eat tunnels into the wood, destroying a tree's water and nutrient system and its ability to feed itself.

The emerald ash borer likely arrived in the United States in the late 1980s, Liebhold said. It originated in Asia. More than a decade passed before its damage became apparent.

“If it had been discovered five years earlier, it probably could have been eradicated,” Liebhold said.

The woodpeckers don't mind. They peck away the bark to get to the insects and others that move in once the tree dies.

Red-bellied woodpeckers and the nuthatch likely discovered the new food source first, with competition causing the short dip in the other woodpecker species, researchers concluded.

That the birds would thrive from the new food source and nesting areas in dead ash trees makes sense, said Bob Mulvihill, an ornithologist at the National Aviary in the North Side.

“It becomes a smorgasbord of grubs and other insects,” he said. “Birds really are opportunistic. They will begin to work those trees over.”

Jason Cato is a staff writer for Trib Total Media. He can be reached at 412-320-7936 or

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