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We’re losing the rat race

INSIDE Toronto’s rodent population is booming, study finds

Of the 16 cities the study analyzed, 11 had significant spikes in rat populations, led by Washington, San Francisco and Toronto.

This article was written by Amy Dempsey Raven and Kate Allen, and was published in the Toronto Star on February 1, 2025.

Toronto’s rat population is growing faster than the rodents of New York City, Chicago or Amsterdam, according to a new study, illuminating how climate change and urbanization are turbocharging rat growth in the absence of effective control strategies.

Residents who have complained for years about a perceived rodent surge now have peerreviewed evidence, published in the journal Science Advances on Friday, that lays bare the scale of Toronto’s problem. Of the 16 cities analyzed, Toronto had the thirdfastest growing rat population.

The scientists who led the research say their findings should compel cities to invest in coordinated mitigation strategies — or in Toronto’s case, create one in the first place. City officials have been tasked to produce a rat strategy by later this year, after two previous efforts were shelved.

Currently, Toronto does not have a dedicated department or officer in charge of tackling its booming rat population.

“For a city of that size, that’s a glaring omission,” said Jonathan Richardson, a professor of biology at the University of Richmond in Virginia and the new study’s lead author. Richardson’s research was prompted by news reports from different cities complaining of rising rat problems. As an urban ecologist, he wanted to put real numbers to those concerns.

“Naively, I was like, OK, let’s just dive into this and get all the data that’s available, and we’ll be able to do this for dozens, if not a hundred cities, and see what’s happening,” he said. “But it turned out, data was really hard to come by.”

Because so few cities had reliable longterm rat data, the scientists were “pretty discouraged” to only get information from 13 U. S. cities and three internationally.

The study relies on public complaints, which in Toronto come from the 311 reporting system. While Richardson and others said this type of data is imperfect — it can’t reliably demonstrate differences among neighbourhoods, for example, because people with insecure citizenship or rental status may be less likely to report — it can still illustrate longterm trends.

“It’s the best we have, at the moment, to answer a question like this,” said Kaylee Byers, a senior scientist with the Pacific Institute on Pathogens, Pandemics and Society at Simon Fraser University, who was not involved in the study, but spent years researching urban rats and disease ecology as part of the Vancouver Rat Project.

To learn how rats are establishing themselves in cities and responding to climate change, “we really want to invest in municipal strategies that track actual numbers of rats across cities and over time,” Byers said.

Cities aren’t doing that because tracking rats is expensive, timeconsuming and often not a top priority, she added.

Of the 16 cities the study analyzed, 11 had significant increases in rat populations, led by Washington, San Francisco and Toronto. Only three experienced declines: Tokyo, New Orleans and Louisville, Ky.

When the scientists analyzed the relationship between these trends and the urban environment, they found that the biggest influence on rat growth was climate warming: the cities that saw the biggest temperature increases over their historical baseline average also saw larger booms in rat numbers.

Toronto is 1.9 degrees warmer than its historical average, the fastest warming city in the study after New York, according to the study’s data.

Experiments in lab rats have shown that they are very responsive to temperature, Richardson explained. Cold temperatures act like a brake on rat reproductive cycles, and warming releases that brake. Foraging gets easier too. Fewer rats die in deep winter if those periods get warmer. It’s unclear which of these is happening, or if it’s all three.

After climate warming, urbanization and population density also had a big impact, likely because they create more habitat and food sources for rats to exploit.

Study coauthor Bobby Corrigan, a rodentologist who leads New York City’s Rat Academy, said that when green space is replaced by buildings, it creates more “subterranean infrastructure” — underground pipes, sewer lines and crevices — where rats thrive.

“There is a rat world right below our feet,” Corrigan said, but it’s difficult to examine those spaces .

City of Toronto staff declined to provide more details about the inprogress rat action plan, or say if it would move up its completion due to residents’ concerns.

“Like most major cities, rodents are common in Toronto,” said spokesperson Russell Baker. “While the City of Toronto is unable to track the total rodent population in Toronto,” the city is “always open” to trying to improve its rodent control, Baker said, citing last year’s direction from council to explore an “interdivisional action plan,” due later this year.

This is not Toronto’s first attempt at creating a rat strategy.

In 2018, after what became known as “the summer of rats,” city council asked staff to come up with a plan. A policy team worked for 18 months, but it was never finished. City staff said it was shelved due to pandemicrelated resource constraints.

Since then, rodentrelated property standards complaints have shot up 70 per cent, prompting the latest push for a strategy.

The study authors said their findings make a case for cities to commit more resources to rat mitigation and start collecting reliable and systematic data.

Urban rat strategies should focus on integrated pest management, which emphasizes monitoring, removing food sources ( namely, trash) and shoring up infrastructure weaknesses as first steps, with chemical tools such as rodenticide baits meant to be a last resort, said Corrigan.

Corrigan, who works for the New York City Department of Health, said we should beware rats’ potential as carriers of disease pathogens.

“The big takeaway is this is not going to get better,” Corrigan said, as climate change creates a more favourable environment for urban wildlife. “And the question is, are we ready?”

“ The big takeaway is this is not going to get better. BOBBY CORRIGAN RODENTOLOGIST WHO LEADS NEW YORK CITY’S RAT ACADEMY

RODENT COMPLAINTS IN TORONTO RELATED TO PROPERTY STANDARDS VIOLATIONS

Climate change driving up Toronto rat numbers: study

This article was written by Ivan Semeniuk and was published in the Globe & Mail on February 1, 2025.

For city dwellers around the world, the effects of climate change have been widespread and sometimes detrimental, including challenges to air quality, infrastructure and public safety.

But a new study of northern hemisphere cities including Toronto shows that rising global temperatures have benefited at least one urban group: rats.

According to the research, rat populations have been on the rise for at least a decade in the majority of urban centres where data are available. The environmental factor that tracks most closely with rodents’ surging numbers is climate.

The results suggest that without proactive measures – such as better management of garbage and other food sources – issues with rats are likely to increase. This is especially in northern cities, where the rate of warming temperatures caused by fossil fuel emissions is more pronounced than the global average.

“We think we’re explaining the majority of the variation in rat trend numbers across the cities,” said Jonathan Richardson, a biologist at the University of Richmond in Virginia who led the work. “Long-term increase in temperature was by far the strongest predictor.”

Rats are a ubiquitous presence in most cities and a concern for public-health officials because of their potential to spread disease. Even so, comparative, systematic studies of rats across multiple centres are surprisingly scarce.

For their own study, published Friday in the journal Science Advances, Dr. Richardson and his colleagues gathered data from cities on three continents to try to tease out what the numbers are showing. That meant zeroing in on locations where rats have been consistently monitored for a long enough period of time to establish a trend.

Despite public concern about the rodents, they found that – for most municipalities – such information simply does not exist.

“Nobody really knows exactly how many rats live in any city,” said Maureen Murray, a wildlife disease ecologist with Chicago’s Lincoln Park Zoo and a co-author on the study.

To overcome this challenge, the researchers focused on cities where they could access public complaints and inspection reports to get a sense of how rat numbers are changing over at least a seven-year period.

Only sixteen municipalities met those criteria, nearly all in North America, with Toronto as the lone Canadian city in the study. It scored the third highest behind Washington and San Francisco in showing a significant trend toward increasing rat numbers.

Next, the researchers tried to tease out which factors might have an effect on rat populations regardless of how rats were being counted. These included population density and degree of urbanization, which can influence availability of food and habitat, and gross domestic product (GDP), which speaks to the resources a city may be able to draw on for rat management.

Researchers also considered two climate-related factors for each city – the long-term temperature increase and the average minimum temperature.

Among all factors, it was longterm temperature increase that showed the strongest association with increasing rat numbers.

Dr. Murray said that this squares with what is known about the rat’s reproductive rate, which increases in tempo when temperatures rise and food tends to be more available.

“This animal has evolved to reproduce as quickly as possible,” Dr. Murray said.

For cities such as Toronto, which oscillate between cold and warm periods through the year, the study suggests that climate change is allowing rats to spend more time operating at their peak reproductive rate.

Among the factors that were least correlated with rat sightings was GDP, which indicates that wealthy cities are doing as poorly as cities with fewer resources when it comes to managing the problem. This points to a lack of forward planning in containing rat numbers before they balloon, Dr. Murray said.

“Being proactive about rat issues, understanding where the biggest issues are, monitoring sanitary conditions and improving those before you have a rat problem, are so important,” she added. “Because preventing rats is much, much more possible than exterminating rats that have already become established.”

Kaylee Byers, a public-health researcher at Simon Fraser University in Vancouver who was not involved in the study, said there are plenty of reasons to pay attention to rats in urban environments. Among the diseases that rats are known to carry is leptospirosis, a bacterial infection that can be fatal to humans and dogs and can be contracted from rat urine. More broadly, the presence of rats in or near where people live is known to negatively impact mental health.

Dr. Byers said the study’s authors did admirable work with the information available but she added data based on public reports can be affected by numerous factors, including how accustomed people are to the presence of rats and which cities are more or less likely to receive complaints about the rodents.

“It’s the best data we have, but it’s not perfect data,” Dr. Byers said. “I think it’s a really interesting first look and it points towards future questions that we should be asking.”

Those questions could include why four cities in the study – New Orleans, Louisville, St. Louis and Tokyo – showed a decreasing trend in rat reports, presumably for local reasons unrelated to climate.

Dr. Richardson said there was plenty of scope for further work, as well as public interest in the science. “Most people when they find out I study rats, they’re like, ‘Oh gross, but tell me more.’ ” he said. “There’s a visceral repulsion – but also intrigue.”

Orcas turning to Arctic waters

Receding sea ice could be bad news for other whales, and humans too

This article was written by Nono Shen and was published in the Toronto Star on December 27, 2024.

**According to a study, killer whales in the eastern Canadian Arctic have been observed preying mostly on beluga whales and narwhals, followed by bowhead whales and seals.**

Killer whales are expanding their territory and have moved into Arctic waters as climate change melts sea ice, with two genetically distinct populations being identified by Canadian scientists.

But their study said that could have “severe consequences” for potential prey whales such as belugas, narwhals and bowheads, that lead researcher Colin Garroway called “slow, chubby and delicious.”

Garroway, an evolutionary geneticist at the University of Manitoba, said the situation was complex — the Arctic orcas have the potential to upend ecosystems as apex predators, even as they merit conservation concern.

The study said the orcas could also affect humans, by “adding topdown pressure on Arctic food webs crucial to northern communities’ social and economic wellbeing.”

It said killer whales in the eastern Canadian Arctic have been observed preying mostly on beluga whales and narwhals, followed by bowhead whales and seals.

“We think there’s going to be a big change in the community structure and how these different creatures interact,” said Garroway.

The study said the Arctic is the fastwarming region on the planet, and as sea ice retreats, its waters are opening to traditionally subArctic species such as killer whales.

Garroway said killer whales were once thought infrequent Arctic visitors, since they risked breaking their famous dorsal fins on ice.

But sightings have become more frequent.

Garroway said researchers took tissue samples from the orcas “and we were super surprised that there are actually two highly distinct populations.”

“I was like — I didn’t believe it, and then I dug in and dug in and … it’s all pretty straightforward stuff to do when you have the data. And, sure enough, there were two distinct populations,” said Garroway, adding that they numbered in the hundreds.

The study, published in “Global Change Biology” in June, describes one group as “globally genetically distinct” while the second is similar to killer whales from Greenland.

Garroway said the two Arctic orca groups have different feeding behaviours and vocalizations, and don’t recognize each other as potential mates.

Hundreds of thousands of beluga, narwhal, bowhead, sperm whales, and bottlenose whales live in the Arctic orcas’ territories, he noted.

“Now that there’s no ice cover, we think that’s one of the things enticing the killer whales in,” said Garroway.

“There’s all these slow, chubby, and delicious whales in the Arctic that are easier to get than otherwise … It’s interesting to see more killer whales in the Arctic, and being top predators, they can disrupt the ecosystem.”

The study notes that the orcas’ prey species are “culturally and economically important to Indigenous communities, so these species also merit conservation and management concern in light of killer whale populations moving into the Arctic.”

Garroway said that during the research period, which lasted several years, the team heard from Indigenous groups from northern communities who expressed concerns about killer whales moving in and hunting food that was “crucial” to their communities.

“That’s what makes it all so confusing because the killer whales themselves are an at risk population and it’s all changing,” said Garroway.

Sea turtles stranded by climate change fill New England animal hospital

This article was written by Rodrique Ngowi and Patrick Whittle, and was published in the Globe & Mail on December 4, 2024.

**Workers examine a Kemp’s ridley sea turtle at the New England Aquarium in Quincy, Mass., on Tuesday. Cold-stunned sea turtles wash up on Cape Cod every fall and winter.**

As global warming fills the plankton-rich waters of New England with death traps for sea turtles, the number of stranded reptiles has multiplied over the past 20 years, filling one specialized animal hospital with the endangered creatures.

The animals enter areas such as Cape Cod Bay when it is warm, and when temperatures inevitably drop, they can’t escape the hooked peninsula to head south, said Adam Kennedy, the director of rescue and rehabilitation at the New England Aquarium, which runs a turtle hospital in Quincy, Mass.

More than 200 cold-stunned young turtles were being treated there Tuesday, Mr. Kennedy said.

“Climate change certainly is allowing those numbers of turtles to get in where normally the numbers weren’t very high years ago,” he said.

Cold-stunned sea turtles, sometimes near death, wash up on Cape Cod every fall and winter. The aquarium expects the number of turtles it rescues to climb to at least 400, Mr. Kennedy said. In 2010, the average was 40, he said.

The total five-year average of cold-stunned sea turtles in Massachusetts was around 200 in the early 2010s, according to National Oceanic and Atmospheric Administration data, growing to more than 700 in recent years.

All the turtles at New England Aquarium’s hospital are juveniles, mostly critically endangered Kemp’s ridley sea turtles whose migratory patterns fuel their strandings here. They are being treated for maladies ranging from pneumonia to sepsis.

The Kemp’s species – the world’s smallest sea turtle – lives largely in the Gulf of Mexico and ventures into the Atlantic Ocean when juvenile.

Some recent science, including a 2019 study in the journal PLoS One, says the warming of the ocean increases the chance of cold-stunning events once the turtles reach the Northwest Atlantic. Warmer seas may have pushed the turtles north in a way that makes stranding more likely, the study said.

The turtle hospital allows the animals to rehabilitate so they can be safely returned to the wild, sometimes locally and sometimes in warmer southern waters, Mr. Kennedy said.

Upon arrival, the turtles are often critically ill.

“The majority of the turtles arrive with serious ailments such as pneumonia, dehydration, traumatic injuries, or sepsis,” said Melissa Joblon, director of animal health at the aquarium.

Around 80 per cent survive. High wind speeds and dropping temperatures have played a role in recent strandings, Mr. Kennedy said.

Some of the turtles that arrive at the hospital are green turtles or loggerheads, which are not as endangered as the Kemp’s ridley, but still face numerous threats.

INSIDE Toronto’s rodent pop­u­la­tion is boom­ing, study finds

Receding sea ice could be bad news for other whales, and humans too

INSIDE Toronto’s rodent population is booming, study finds