Urban stormwater ponds provide important habitats for birds including both resident and migrating species, according to a new University of Toronto study published in the journal Urban Ecosystems .
For the study, researchers placed audio recorders at 16 stormwater ponds in Brampton, Ont., and used AI-based sound identification software to identify birds by their calls.
A total of 145 bird species were detected, including nine considered at-risk, with vegetation features such as cattails, submerged plants and trees acting as predictors of which species appear at a given pond
"Every pond is different," said the study's senior author Donald Jackson, a professor in the department of ecology and evolutionary biology in the Faculty of Arts & Science. "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."
Stormwater ponds are artificial reservoirs dug in residential areas to mitigate flooding by collecting runoff water that would otherwise flow from storm sewers into streams. Although not intended as natural habitats for wildlife, they have become home to insects, amphibians, fish, small mammals and birds.
In the past, researchers surveyed stormwater ponds by spending relatively short periods of time at locations and identifying birds visually or by their calls. This method likely overlooked rare, nocturnal and hard-to-identify species.
The use of advanced sampling methods by Jackson and Kaylie Borntraeger, an undergraduate student and lead author of the study, is helping paint a more accurate picture of the importance of stormwater ponds as bird habitats - with Jackson noting the study found twice the diversity in bird species that was reported in previous studies of urban ponds in southern Ontario.
Of the 145 species identified in the study (Ontario is home to some 300 species of birds), the most common were American goldfinches, American robins, red-winged blackbirds and song sparrows. The nine species classified at-risk in Canada were barn swallows, bobolinks, chimney swifts, eastern meadowlarks, eastern whip-poor-wills, least bitterns, peregrine falcons, yellow-breasted chats and red-headed woodpeckers.
"I was surprised by the numbers and the variety we found," said Borntraeger, a member of University College who took part in the project via the Centre for Global Change Science's internship program. "We identified many more bird species than I was expecting, including many migrating species."
Despite supporting so many bird species, there are ongoing concerns about the overall ecological health of stormwater ponds.
Jackson's past research has shown that runoff water carries salt from roads to urban waterways, raising chloride concentrations to levels harmful to aquatic species. Fertilizer in runoff can also trigger algal blooms that lead to high levels of bacteria that can produce toxins.
Stormwater ponds can also accumulate heavy metals, pesticides and improperly discarded liquids like motor oil and solvents.
"The danger is that contaminants found in ponds move up the food chain - from larval insects to fish to birds like herons and kingfishers," said Jackson.
What's more, depending on municipality requirements, stormwater ponds may be little more than ponds surrounded by a fence and grass - with none of the other vegetation features that make them 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? Or should we manage them in such a way that they are better habitats for species?" said Borntraeger. "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."
"When we transform forested areas for agricultural purposes, and agricultural areas for urban development, we lose streams, ponds, wetlands [and] wildlife," said Jackson. "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 [ponds] 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."
Jackson said he hopes the study helps raise broader awareness of stormwater ponds as destinations for birds - something many birding enthusiasts are already aware of. "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," he said. "There's lots of opportunity for public engagement and interest."
The research is part of a larger study initiated in 2022 by Jackson's research group and involving Ben Gilbert and Shelby Riskin, associate professors of ecology and evolutionary biology; Nicholas Mandrak, professor of biological sciences at U of T Scarborough; and several 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.
