Of borers and birds

  • Updated: August 11, 2009 - 4:54 PM

The infestation of emerald ash borers is likely to have a negative impact on birds, especially those that nest in ash trees. But this destructive pest may prove to be a boon for one species.

Pileated woodpecker

Photo: Jim Williams, Special To The Star

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If the emerald ash borer visits your yard, the neighborhood woodpeckers will know about it long before you do.

"Woodpeckers are spectacularly successful in finding ash borers," said Michael Raupp, a professor and extension specialist with the Department of Entomology at the University of Maryland.

Woodpeckers listen for the sound of chewing, then hack away at tree bark to expose the borers, grubs, ants and other edibles that are at work within. In fact, they're so good at what they do that "in some of our ash borer test plots it was difficult to find borers because the woodpeckers had taken them all out," said Raupp.

But Raupp, who has long been studying these pests (the borers, not the birds), doesn't think there are enough woodpeckers to solve the emerald ash borer problem. It's likely that there will be way more of the tree-killing insects than the woodpeckers can eat.

I hadn't called Raupp to ask about woodpeckers. I'd wanted to know if there was reason to be concerned about what the two main pesticides used to kill borers might to do birds.

"Both chemicals pose problems," he said, "but there is no direct evidence that either chemical -- imidacloprid or ememactin benzoate -- is going to harm birds," he said. He sees a bigger problem in the loss of the trees.

"It's a matter of weighing the use of poisons against the loss of an entire genus of trees," he said. "I read one Forest Service report indicating there are 80 billion ash trees in North America." About 934 million of those are in Minnesota. "The loss of these trees will have devastating repercussions for natural and managed ecosystems," he said.

John Moriarity, natural resources manger for Ramsey County parks, agreed. Moriarity said he isn't concerned about a threat to songbirds from the poisons that might be used to fight the bug. In fact, he said, woodpeckers might even get a boost from the presence of the borers simply because when food is plentiful, more birds survive and reproduce.

Imidacloprid, one of the weapons against ash borers, is used to keep birds from eating grain. Apparently, it works. It was tested with sunflower seeds on red-winged blackbirds and rock pigeons. When they try to work the nut from the shell of the sunflower, the birds ingested enough imidacloprid to make them retch and become dizzy, sort of like a hangover. Though they recovered in a few hours, they seemed to learn to avoid the treated seeds.

As in everything, however, the dose is the poison.

Lee Frelich of the University of Minnesota Center for Hardwood Ecology told me he couldn't find any studies that tracked the effects of songbirds eating insects on treated trees.

"Imidacloprid seems to have toxic effects fairly specific to insects, with relatively little impact on other life forms," he said.

But, like the other experts I consulted, Frelich sees huge consequences from the emerald ash borer for birds that nest in the ash trees in central and northern Minnesota swamps and our southern floodplains.

"This is probably a more negative impact than the secondary impacts of imidacloprid," he said, adding that "we don't have a clue about emamectin benzoate impacts." (That chemical has been called the ash borer chemical of choice by researchers at the University of Illinois.)

So just how treating for emerald ash borers will affect birds is yet to be determined. The only thing that seems certain is that woodpeckers are about to get lucky. At least for a while.

While it may sound unlikely, it's happened before.

"When Dutch Elm disease killed off most of our elms there was a significant decade-long increase in woodpecker populations," said Jim Kellam, a woodpecker biologist at St. Vincent College in Pennsylvania. "Not all ash borer impacts are going to be negative," he said.

Jim Williams, a lifelong birder, is a member of the American Birding Association, Ducks Unlimited, Pheasants Forever and Delta Waterfowl. Join his conversation about birds at www.startribune.com/wingnut. He can be reached by e-mail at two-jays@att.net.

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