Is climate change really driving the ratpocalypse?


Ticks
,
mosquitoes
, tree-wrecking beetles, locusts.
The list of pests expected to benefit as the planet heats up is
long and getting longer. But what about rats?

The answer is tricky. Headlines have warned about
a coming ratpoclaypse
driven by climate change. But there
isn’t a lot of research to back these warnings up. Part of the
reason is that it’s hard to predict what rats will do, because
it’s harder than you’d think to study what rats are doing right
now.

It took Michael Parsons, a researcher at Fordham University,
almost two years to get three facilities to let him tag rats and
study them. Parsons is one of just a handful of biologists that
studies New York City’s rats. Of those three that granted him
access, Parsons will only describe two as “waste treatment
facilities” in two different boroughs of the city. The third?
“It’s super secret,” he said.

Parsons won’t name the places because, you know, rats. For a
property owner, allowing Parsons to study rats at their facility
means admitting they have a rat problem in the first place. In
2017, Parsons went so far as to
offer $1,000 to anyone
with a rat infestation who’d let him
conduct research on their property. No one’s taken him up on it
yet.

“I have shed more tears over this than probably anything else
in my life,” he said. “It really has been enough to shut down
multiple research studies. We just have it in our culture that rats
are more of a taboo than other urban wildlife.”

It’s also one of the many reasons why we know so little about
rats. Even basic information such as the number of rats in a city
and whether their numbers are growing is hard to come by: Estimates
of New York City’s rat denizens range between 2
million and 32 million
. So understanding the effect of warming
temperatures on urban rat populations is exceedingly difficult.
Despite the scary
headlines
, a search for climate change studies about urban rats
yields no results. Parsons, too, hasn’t come across any research
on the subject.

But this much we know: Rats reproduce at a prolific rate, and
they like warmer temperatures. The brown rat, the one most commonly
found on the East Coast, can give birth to as many as six litters a
year, with 12 pups per litter. For a number of reasons, rats tend
to stay in their burrows longer during the winter. As more people
stay indoors during the colder months, there’s fewer half-eaten
hot dogs and bagels for them to feed on. And the chances of
survival for the pups in winter is lower.

When temperatures are warmer, rats are likely to reproduce more.
So it stands to reason that climate change will give them a boost.
In the United States, spring is starting earlier, and average
summertime temperatures are rising. In New York City, home to the
infamous pizza rat, summer temperatures have increased 2.4
degrees Fahrenheit
since 1970.
A recent federal report
found that on average temperatures
across the country have increased 1.3 to 1.9 degrees.

Warmer temperatures for longer stretches of time also mean rats
may reproduce more, which poses public health problems. Rats serve
as hosts for ticks and fleas and carry diseases such as Salmonella
and bubonic plague (the disease that brought us the Black Death).
Add to this the fact that warmer temperatures
allow ticks
and fleas to breed longer and spread to new parts
of the country, and the problem begins to compound.

Parsons, the Fordham University researcher, says that for these
reasons, city rats need to be better understood. But trying to
catch, tag and track them is difficult. The most commonly cited
data when talking about changes in rat populations are calls to
311, New York City’s government-services and complaint line. News
articles on the subject cite an increase in 311 calls about rats in
the last few years. In New York City, rat-related calls
increased by 10 percent
last year compared to 2016. Washington
D.C., Chicago and Boston have also seen increases in rat complaints
in the last few years. But these calls aren’t a direct measure of
the number of rats in a city. Rather, they measure the number of
people who spotted a rat — then decided to make a call about
it.

What might influence a person to call in a rat sighting? Whether
they’re accustomed to seeing rats is part of it. Another is
whether they believe calling will lead to a response from the city.
The more upscale the neighborhood, the more likely someone is going
to complain about a rat sighting, Parsons said. That might explain
why the well-heeled Upper West Side in New York City logged the

highest number of rodent-related complaints
in 2017.

“No one really knows if rat populations are increasing or
decreasing,” said Chelsea Himsworth, who leads the
Vancouver Rat Project
as a regional director for the Canadian
Wildlife Health Cooperative. “I’ve never come across any
reliable data.”

Still, Himsworth believes that rat populations are increasing
because cities are growing and getting more densely packed.

Himsworth said warmer temperatures might help rats but that the
knock-on effects of climate change will likely play a larger role.
If a city floods more often as a result of climate change, for
instance, waste management systems are more likely to falter, and
more garbage winds up in the streets. “Rats are going to
capitalize on chaos [and] climate change guarantees unpredictable
events,” she said.

Another big unknown, Parsons said, is how people might respond
to real or perceived increases in the number of rats. An aggressive
response could limit their growth. In 2017, New York City Mayor
Bill de Blasio declared a war on rats and invested $32 million in
rat reduction measures. His plan included hiring more
exterminators, new trash bins and cementing dirt basements in
public housing.

In the end, as with climate change, it comes back to how humans
behave. “A lot of how rats respond to climate change depends upon
how people respond to rats that are responding to climate
change,” said Parsons.

This story was originally published by Grist with the headline
Is climate change really driving the ratpocalypse?
on Jun 5,
2019.

Source: FS – All – Science – News
Is climate change really driving the ratpocalypse?