As development grows, so does decline of this songbird that calls Ontario's Waterloo region home

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." 

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."