As ash trees die, some birds thrive

Woodpecker, nuthatch numbers may rise here: study

The death of ash trees provides a “feast for woodpeckers,” says a new study that forecasts a likely population boom among Ottawa’s woodpeckers and nuthatches.

Emerald ash-borer beetles kill ash trees by laying eggs under the bark. The emerging young ash borer does the damage, eating its way around the tree and cutting off the flow of nutrients up the tree.

But the Cornell University Lab of Ornithology found that the young borers — up to 60,000 per ash tree — have led to a population boom among insect-eating birds in the Windsor-Detroit area.

Michigan was one of the first areas to suffer large number of ash deaths after the insect arrived in North America.

Cornell’s Walter Koenig and his team studied four species: downy, hairy and red-bellied woodpeckers, and whitebreasted nuthatches, from 2003 to 2011.

During that period, ash borer killed at least 75 per cent of the ash trees in the hardesthit region.

The number of nuthatches and red-bellied woodpeckers immediately grew when the ash-tree epidemic became serious, they found.

The downy and hairy woodpeckers had a drop in numbers for the first couple of years, followed by growth. The team can’t tell why, and notes that upsetting an ecosystem sometimes has results no one could have predicted.

Koenig thinks any increase in woodpeckers would be temporary, and he won’t even guarantee that Ottawa will see an exact repeat of the Detroit experience.

He’s pretty sure we’ll see some increase, though.

“This is why we have ecologists,” he said in an interview. “Because we just don’t know.”

The insects bring at least two benefits for the birds. They’re a supply of woodpecker food, and they also create opportunities for the birds to nest in cavities of decaying trees.

Woodpeckers haven’t become more common here yet, but birder Bruce Di Labio expects they will once more Ottawa ash trees die.

“The downy woodpecker would definitely be one (that would increase here) and possibly the hairy,” he said.

Red-bellied woodpeckers are a more southern species, still rare here, he said. The study is published in a science journal called Biological Invasions.