Urban pest species are on the rise thanks to climate change — and city authorities are resorting to increasingly inventive methods to control them.
Rising temperatures are creating ideal conditions for pests such as rats and pigeons to reproduce more quickly, as well as introducing new species. That’s creating an urgent public health problem for city governments.
“We’ve long anticipated that climate change would become one of the most significant threats to biodiversity,” said Kris Murray, ecology and public health expert at Imperial College in London.
“But it turns out that different species respond differently to different threats, and some species … may actually thrive as a result of climate change and urbanization.”
Here’s how cities are tackling three pest species that are benefiting from warming cities.
In Brussels, milder winters have caused the pigeon population to boom, prompting the authorities to trial new methods for keeping numbers in check.
“Pigeons are producing more offspring” as a result of the warmer weather, said Zoubida Jellab, the city of Brussels’ alderwoman for green spaces and animal welfare. “They produce a lot of excrement … and the result is that there is a lot of shit to be cleaned up in public spaces and off older buildings.”
On average, a single pigeon can produce up to 12 kilos of droppings a year; beyond sullying public spaces, those feces can contain bacteria that create a health risk.
Capturing and killing pigeons is forbidden in the Brussels region. So the city has adopted an animal-friendly strategy to keep bird numbers down: installing bird feeders stocked with contraceptives that temporarily make the female birds infertile.
“[The method] is much more humane than capturing and neutering them — something that was done 10 years ago — or killing them with poison, guns or other animals,” according to Jellab.
The alderwoman said the strategy, which was first trialed in 2019, has been successful so far, with pigeon numbers dropping by up to 50 percent in places like Square Clémentine in the district of Laeken. The city is now expanding the program to other parts of Brussels.
With climate change “causing disturbances” in city animals’ breeding patterns, Brussels is looking to “keep the balance between the wellbeing of people and the wellbeing of animals living here,” said Jellab.
That balance will become increasingly difficult to strike, according to Murray.
The likeliest scenarios for climate change in the years ahead will create favorable conditions for species “that are basically parasites,” he said. “The evidence we have suggests we should be alarmed about what new or re-emerging diseases they may bring.”
Pigeons aren’t the only species multiplying as the climate changes; cities have also seen a dramatic rise in the number of rats, as warmer temperatures allow them to keep their litters warm in winter and reproduce year-round.
“The shorter frost periods, as well as the quantity of food resources available in the public space … has led to a visible increase in rodent populations in large cities,” said Françoise Ampoulange, the municipal counselor in charge of animal welfare in Toulouse.
The French city is experimenting with a new tactic for dealing with the rat population, using ferrets to rein in the number of rodents.
“Traps are placed at the burrow exits and up to three ferrets are released to flush the rats out,” Ampoulange explained. “Traditional traps generally only catch younger rats, but this system is successful at catching the ‘alpha’ couples that produce the colony’s litters.”
The strategy is a useful alternative to conventional systems, given there are strict rules on the use of poisons, Ampoulange said. The rats caught by the ferrets are then euthanized with gas.
Scientists say Europe will also have to brace for new types of pests and the return of others that have been gone for decades.
Warmer temperatures on the Continent are expanding the range of invasive mosquito species, for example, according to Murray.
“Aedes aegypti mosquitoes can carry devastating viruses like dengue, yellow fever, zika and chikungunya,” he said. “Our projections show that these may be common in Europe by the end of the decade.”
Many invasive mosquitoes were responsible for disease outbreaks in European cities during the first half of the 20th century, but they disappeared as a result of a few harsh winters and better mosquito management practices.
Now climate change is already causing them to reappear in southern Europe.
“The increase in temperature is broadly supportive to the development of this and other mosquito species, like the Asian tiger mosquito, which has already been detected as far north as the U.K. and was implicated in an outbreak of dengue in France this year,” said Murray.
He added that the need to store water in increasingly dry areas of Europe, like Spain, Portugal and Greece, would inevitably create environments where these kinds of mosquitoes thrive.
“Cities are going to have to do more to address mosquito management, developing better standards for water tanks and even deploying teams of people to check domestic flower pots and bird baths for standing water,” he said.
But even that might not be enough, he cautioned.
“The Asian tiger mosquito has already been found wintering in sewers even in places with very deep snow,” he said. “They’re arriving with the warmer temperature and developing ways to survive until the next season and bounce back.”
Giovanna Coi contributed reporting.
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