Ontario researchers link declining wood thrush numbers to housing and other development | CBC News

Population numbers for a migratory songbird that calls Ontario’s Waterloo region home have been on a steep decline over the past 20 years, and housing and other developments built around their habitat may have something to do with it.

Researchers with the University of Guelph (U of G) looked at wood thrush bird abundance and nest success from 70 woodlot sites across the region from two decades ago, and compared the findings with data they recently collected on those same sites.

“The first thing we found was that there were no wood thrush in a lot of the places they use to be in,” said Karl Heidi, one of the lead researchers who now works for Ontario Breeding Bird Atlas.

According to the Ontario government, the wood thrush lives in mature deciduous and mixed (conifer-deciduous) forests. While the birds prefer large forests, they’ll also use smaller stands of trees and build nests in living saplings, trees or shrubs.

Heidi said that for their research, they only found the bird in about a third of the 70 woodlot sites.

“It’s telling us that there’s been a strong decline in the population, which is what we have seen across the range of the bird,” he said. 

“These birds also live in the United States across the Appalachians and other parts of the east, and there’s been a noticeable decline in those areas as well over the last 30 or 40 years.”

Their research found the drop in wood thrush numbers was strongest in sites that had development and housing built around them.

“We recorded a 79 per cent decline of wood thrush in forest fragments that experienced development around that fragment,” said Ryan Norris, an associate professor in the department of integrative biology at U of G who was also part of the study.

“If you put houses around a forest fragment, you have a good chance of losing wood thrush in the forest fragment.” 

Wood thrush are sensitive to change

Heidi said wood thrush, unlike robins or cardinals, are sensitive to any kind of change or disruption around their habitat. 

“These migratory birds just aren’t adapting as well to change, and you notice it when you’re in the field that they are more skittish and wary of people than would be a robin or chickadees.”

He also pointed to growing changes to the wood thrush’s wintering grounds in Central America and other issues that come up during migration, such as window collision and urban light pollution, as potential contributors to their decline.

The Ontario Ministry of the Environment, Conservation and Parks said the wood thrush is a species of “special concern,” which means it’s not endangered or threatened but could be under a “combination of biological characteristics and identified threats.”

The ministry’s website lists loss of forest habitat from urban, suburban and cottage development as one of the major threats faced by the bird.

Norris and Heidi said the decline in population is concerning and they worry about the wood thrush’s future.

“We’re losing the abundance of the bird, but the birds that are remaining are tending to do OK in terms of nest success, but that’s not enough to compensate the loss of the size of the population,” Norris said. “It is at risk, no doubt.”

Heidi feels the same.

“It’s probably been tens of thousands of years since it first evolved in this region, so to see this kind of a decline over what’s really a blink of an eye in its history is really alarming.”

Population decline could have wider implications

Losing the wood thrush probably wouldn’t impact day-to-day life, Norris said, but we should care because what’s happening to this bird is likely happening to others.

He said birds play an essential part in the ecosystem and losing large numbers could have wider implications.

“We can’t always predict what will happen because it’s such a complex machine, the ecosystem, but migratory birds are a big cog in that ecosystem.”

Now that the study has wrapped up, Heidi will head to the Sudbury area in northern Ontario over the summer to study wood thrush there. 

This study is only the beginning of a larger project looking into bird population changes as a whole across Waterloo region in the last 20 years.

“Being able to see what the changes were in this region after 20 years of development is really crucial because we had so much historical data, and now we have the current status of things which is very useful,” he said.