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 smallmammals. 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 Adelaideand 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, sprayedand 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 ofcontrolling 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 KleinSC
OTT^ RAP
SONNews
The Felixer grooming trap
can spray a lethal gel at
feral cats2 million
Australia plans to cull this many
feral cats by 2020MathematicsWe finally know
the odds of winning
a game of solitaireTHERE 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 famousvariant 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 foreach. 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 issimilar 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 MackenzieWildlifeToxic 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”