By Chris Sasaki

During the COVID-19 pandemic, with provincial parks and conservation areas closed, birders resorted to ‘patch birding.’ They found birds in whatever ‘patch’ of nature was available to them — backyards, local parks or neighbourhood stormwater ponds.

Stormwater ponds (SWPs) are artificial reservoirs dug in residential areas to mitigate flooding by collecting runoff water that would otherwise flow directly from storm sewers into streams. While not intended as natural habitats for wildlife, they have nonetheless become home to insects, amphibians, fish, small mammals and many species of birds.

The department’s Donald Jackson is a professor of aquatic ecology who studies aquatic ecosystems — including lakes, rivers, streams and SWPs — and the species that call those habitats home.

In a paper published in the journal Urban Ecosystems, Jackson and an undergraduate student, Kaylie Borntraeger, describe the results of their census of bird species found in 16 SWPs in Brampton, Ontario.

“In terms of the number of bird species, we found twice the diversity that had been reported in previous studies of urban ponds in southern Ontario,” says Jackson.

“I was surprised by the numbers and the variety we found,” says Borntraeger, a member of University College who took part in the project thanks to the Centre for Global Change Science’s internship program. “We identified many more bird species than I was expecting, including many migrating species.”

According to Jackson and Borntraeger, the numbers show the importance of SWPs as habitats for migratory and resident birds, and demonstrates their potential as aquatic ecosystems as urbanization paves over natural environments like creeks, ponds, fields and forested areas.

While SWPs are home to many birds, there are factors that can make them anything but healthy ecosystems.

Overall, Jackson and Borntraeger identified 145 species. (Ontario is home to about 300 species of birds.) The most commonly found species were American goldfinches, American robins, red-winged blackbirds, and song sparrows. Of the species identified, nine are classified as at-risk in Canada: barn swallows, bobolinks, chimney swifts, eastern meadowlarks, eastern whip-poor-wills, least bitterns, peregrine falcons, yellow-breasted chats and red-headed woodpeckers.

In past surveys, researchers collected data using traditional sampling approaches; they would spend relatively short periods of time at locations and identify birds visually or from their calls. This likely overlooked rare, nocturnal or hard-to-identify species.

To achieve a more accurate survey, Jackson and Borntraeger collected data using audio recorder units left onsite. They then used AI-based software that identified species according to their calls — similar to Merlin, the popular bird-call app used by many birders.

While Jackson and Borntraeger have shown that SWPs are home to many birds, there are factors that can make them anything but healthy ecosystems.

As Jackson’s own research has shown, runoff water carries salt from roadways into urban waterways, raising the concentration of chloride to levels harmful to aquatic species. Fertilizer in runoff can trigger algal blooms in ponds which can lead to high levels of cyanobacteria that can produce toxins. SWPs can also accumulate heavy metals, pesticides, improperly discarded liquids like motor oil and solvents, even chlorine from swimming pools.

“And the danger is that contaminants found in ponds move up the food chain — from larval insects, to fish, to birds like herons and kingfishers,” says Jackson.

What’s more, depending on the municipality’s requirements, SWPs may be nothing more than ponds surrounded by a fence and grass, with none of the trees, aquatic plants, cattails and other vegetation that would make them more conducive to wildlife.

“So, it raises the question: should we manage these ponds so they aren’t habitats and aren’t welcoming to wildlife, as some would like?” says Borntraeger. “Or should we manage them in such a way that they are better habitats for species?”

“As we’ve shown, birds are using them in large numbers and it would be difficult to deter them; so, in my view, it makes sense to improve the conditions in the ponds to make them even better ecosystems.”

Donald Jackson: “When we have stormwater ponds, they help restore some of the lost components of nature.”

According to Jackson, “When we transform forested areas for agricultural purposes, and agricultural areas for urban development, we lose streams, ponds, wetlands, wildlife. So, when we have stormwater ponds, they help restore some of these lost components of nature.”

“Plus, they not only benefit the people living by the ponds, they also benefit developers who initially weren’t happy because the SWPs took up lots that would’ve held housing. Now, they see the positive side — that the lots near these ponds are much more valuable to homebuyers.”

The recently published paper is part of a larger study begun in 2022 of the water quality and ecology in 50 SWPs in Brampton. The study was begun in 2022 by Jackson’s research group and also involves Ben Gilbert,  Nicholas Mandrak, and Shelby Riskin, along with many graduate and undergraduate students. The work is being done in collaboration with the City of Brampton, Toronto and Region Conservation Authority (TRCA), Credit Valley Conservation, and Fisheries and Oceans Canada — and is funded by NSERC Canada.

“Every pond is different,” says Jackson. “And there’s still lots to be learned about how we can best manage these habitats. The research will hopefully influence policy and help guide developers, municipalities and conservation authorities.

“What’s more, while some birders are aware SWPs attract birds, the broader public probably isn’t,” he says. “Much of the public doesn’t even know why these ponds exist or what their function is. So, they could provide great entry points for introducing people to nature — particularly young people. There’s lots of opportunity for public engagement and interest.”

Originally published March 9, 2026, on University of Toronto Faculty of Arts & Science News.