Bird populations can tell the story of development
University of Guelph study looked at impact on wood thrushes as a measure of growth on region’s biodiversity
A NEW STUDY OUT OF
the University of Guelph is able to offer rare, clear conclusions about the impact of development on biodiversity.
“There’s very few data available on pre- and post-development,” said Ryan Norris, an associate professor at the University of Guelph and a researcher on the project. “Pick a woodlot on the outskirts of Waterloo Region that housing is going to be developed on in the next 10 years. Now, we need data from those woodlots now. And then we go back and get data once the houses are up. That’s very rare data. First of all, it takes a long time to collect.”
Norris said develop
ers are required to hire consultants to collect data on biodiversity before and after development, but this data is not made available to the public, and belongs to the developers.
He says long-term studies about biodiversity and populations in an area before it’s developed are rare.
“It’s the value of long term studies. Without long term studies, we don’t really have a very good idea of how animal and plant populations are responding to the environment. So this is a super unique opportunity to look at the long term data in the context of, if houses went up or did they not go up in the intervening time.”
Norris helped collect data on wood thrush populations in Waterloo Region
for his first bird-related job as an undergraduate student with Lyle Friesen of Environment Canada.
Norris helped Friesen collect information on wood thrush populations in the region’s forest fragments in the mid-1990s.
Friesen’s project had data on the region’s wood thrush populations from 1987 to 2001, with many of the forest fragment sites in Woolwich and Wellesley townships. Norris and the team revisited the sites to see how urbanization impacted thrush populations decades later in 2020 and 2021. They visited 72 sites, and some 20 to 30 of the sites were in Woolwich and Wellesley townships.
Norris says that overall, Waterloo Region’s wood thrush population has declined by about 75 per
cent in the last 20 years.
“I’ve been very interested in both forest songbirds and landscape ecology since a young age,” said Karl Heide, another primary researcher on the study. He says he wanted to study the effects of development on forest
birds that live in the forest patches around our cities and in our region.
“As a teenager I remember hearing a wood thrush singing in my local woodlot in Mississauga in late May a couple years, but by June it was nowhere to be found, and I wondered
what it was about the site that forced it to leave.”
Since Norris had been working on collecting data on wood thrush in the forest fragments around Waterloo Region two decades ago, some of the forest fragments became surrounded by urbanization, while others remained rural. Still others had had development next to them the whole time.
Heide and Norris studied abundance – the number of wood thrushes present at each site, as well as nest success, meaning, how well chicks were surviving. They also took note of singing birds which indicates they’ve established territories, said Heide.
“The most important finding was that forest
fragments (woodlots) with new housing built around them over the past 20 years had a steeper decline in the abundance of these birds than in forest fragments that remained in a rural context,” said Heide.
“Putting the development up against what is still there, what remains. It’s reducing the integrity of those places. If it results in wood thrush taking off and other neotropical migratory birds, it reduces the integrity of that place. And it’s no longer the same. It may look to an outsider who has no clue about birds, everything may look good. Everything may look the same, but it’s not and when you start taking species away, that can have repercussions on a place, really big repercussions. So it’s the things that the birds eat. It’s the things that eat the birds, you know, it’s all an ecosystem. So if you start taking away components of it, then that’s when it starts to kind of collapse.”
One important note Norris made is that many of the woodlots they sampled were owned by Mennonite farmers. These woodlots tended to have the best biodiversity, he said.
“Many of the forest fragments that we sampled that did not have development in them during the intervening time period were owned by Mennonite families. Mennonites tend to manage their woodlots quite well,” he said. “I don’t think they’re doing it for biodiversity, but, one, there’s not a lot of people going through the woodlots. And, two, they tend to selectively harvest trees in the woodlots.”
He said selective cutting can be beneficial for birds because it creates gaps in the canopy that allow other plant species to come up, and sunlight to come through and diversifies the habitat in the woodlot. “Those woodlots tend to have the highest diversity of birds in the region.”
Wood thrushes fly south to Central America for the winter, and return to the same spots in deciduous and mixed forests in North America each year to breed, said Norris. He says they are sensitive to changes in their environments that take place while they’re away.
“These are birds that leave during the winter, but they come back. They often come back to the exact same spot. They’ll go down to Mexico, over-winter and come back to the exact same spot. So when you alter that landscape, it can have a detrimental effect on the birds because its surroundings have changed. And I think at that point, the birds just get up and go and leave.”
The team found that the birds that did stay to raise their young experienced higher nest success,