2019-11-23 New Scientist

12 | New Scientist | 23 November 2019

A TRAP that kills feral cats

by spraying them with a lethal

gel they lick off while cleaning

themselves is being trialled

as a way to save endangered

Australian wildlife.

Since their introduction in the

18th century, cats have severely

harmed Australia’s ecology by

preying on native birds and small

mammals. They have contributed

to the extinction of more than

20 Australian animals, including

the paradise parrot, broad-faced

potoroo and rusty numbat, and

continue to threaten many more.

In 2015, the Australian

government set a goal of culling

2 million of the estimated 6 million

cats living in the wild by 2020. But

this has been hard because they

prefer live prey to eating poison

baits and are too numerous to be

controlled by shooting.

To address these problems, John

Read at the University of Adelaide

and his colleagues have invented

an automated device for culling

cats that takes advantage of their

compulsive self-grooming rituals.

The solar-powered device, called

a Felixer grooming trap, has laser

sensors that detect a cat as it walks

past based on its size, shape and

gait. When activated, the sensors

trigger the release of a toxic gel

that squirts onto the cat’s fur.

The cat later licks the gel off

while routinely cleaning its coat.

The gel contains a commonly

used poison called sodium

fluoroacetate, or “1080”, that

halts the production of energy

in cells. The poison is thought to

euthanise cats painlessly because

it causes unconsciousness before

shutting down brain activity, says

Read. An initial trial with two cats

in a pen found they passed out

within 6 hours of being squirted

and died within 10 hours.

As a test, the researchers

recently installed 20 Felixer

devices in a 2600-hectare fenced

paddock in South Australia that is

inhabited by feral cats and native

wildlife. Cameras showed that the

traps correctly identified, sprayed

and killed feral cats, causing

their population to decline by

about two-thirds over six weeks.

No native animals activated the

traps or were poisoned.

In a separate experiment on

Kangaroo Island, the researchers

showed they could prevent pet

cats from activating the traps by

fitting them with special wireless

tags. Read will present the results

at the annual meeting of the

Ecological Society of Australia

later this month.

Some cat protection groups

say the most humane way of

controlling Australia’s feral cats

would be to trap them, surgically

sterilise them and then return

them to the wild. But Di Evans at

animal charity RSPCA Australia

says this is impractical because

feral cats often live in remote,

hard-to-access areas. Felixer traps

are preferable to poison baits

because they specifically target

cats and are therefore less likely to

harm other animals, says Evans. ❚

Alice Klein

SC

OT

T^ R

AP

SO

N

News

The Felixer grooming trap

can spray a lethal gel at

feral cats

2 million

Australia plans to cull this many

feral cats by 2020

Mathematics

We finally know

the odds of winning

a game of solitaire

THERE is now an answer to a

surprisingly tricky problem: what

are the chances of winning a game

of solitaire? It was once called an

“embarrassment” of mathematics

that this couldn’t be solved, but

now a computer program is homing

in on the solution.

Solitaire, also known as patience,

is a single-player card game that

involves sorting cards using certain

rules. Probably the most famous

variant is Klondike, which is often

installed on Windows computers.

Klondike is hard. Renowned

mathematician Irving Kaplansky

once played 2000 games and won

only 36.6 per cent. Later, computers

won more than 80 per cent, but

there was still a huge amount of

uncertainty about the true odds.

To address this, Charlie Blake

and Ian Gent at the University

of St Andrews, UK, wrote a program

to compute the approximate odds

of winning any version of solitaire.

For Klondike, the program dealt

1 million random hands and

computed the best strategy for

each. It had to examine 20 billion

partially played positions, and

calculate sequences as long as

2274 moves to find that you have

a roughly 82 per cent chance of

winning the game (arxiv.org/

abs/1906.12314).

For other variants, the odds

ranged from nearly 100 per cent

for Freecell, which has also often

appeared on Windows, to around

16 per cent for Trigon, which is

similar to Klondike, but has stricter

rules on when cards can be moved.

The pair’s program can’t prove

mathematically what the odds are,

but with a sample of a million hands,

they have reduced the remaining

uncertainty by a factor of 30,

so the estimates should be within

0.1 per cent of the true number.

“We can certainly be less

embarrassed now that we not

only know the winning probability

but have a winning program

that generalises to other games,”

says Prasad Tadepalli at Oregon

State University. ❚

Dana Mackenzie

Wildlife

Toxic goo gun culls feral cats

Australia is testing a device to tackle its devastating feline problem

“ It was once called an

‘embarrassment’ of

mathematics that this

couldn’t be solved”