9 April 2022 | New Scientist | 17WHEN fringe-lipped bats
learn the sound of a dinner
bell, they remember it for years.
The bats’ enduring memory
is comparable to that of other
animals renowned for their
expansive cognitive skills,
such as crows and primates.
Fringe-lipped bats (Trachops
cirrhosus) are native to
rainforests in the Central and
South American tropics. They
are nocturnal predators with
a broad diet, snatching up
insects, frogs, lizards and small
mammals. The bats have a
keen ear and are able to discern
between the calls of poisonous
and non-poisonous prey.
To see how long this ability
sticks around, a team led by
May Dixon at The Ohio State
University in Columbus took
some bats to school.
Dixon and her colleagues
captured 49 fringe-lipped bats
between 2010 and 2018 in
Panama’s Soberanía National
Park. In a flight cage, the
researchers trained the bats
to respond to recordings of
frog calls coming from a speaker
by giving them pieces of fish
when the noise played.
They then played a mix of
frog calls and mobile phone
ringtones, incrementally
reducing the frog call volume
and increasing the ringtone
volume until the bats were
trained to attack the pure
ringtone sounds.
The team then taught the
bats to discriminate between
ringtones, providing a tasty
reward for some sounds and
giving them nothing when
others played.
They were released into the
wild, and eight of them were
recaptured between 1 and
4.2 years later. When they were
played their food-associatedringtones from training, all
eight of the recaptured bats
approached the speaker and
six of them attacked it. When
the researchers repeated this
with 17 wild bats that hadn’t
received the training, only
one approached the speaker
(bioRxiv, doi.org/hnzn).
The researchers note
that remembering auditory
information for 4.2 years is
in line with recall in highly
intelligent animals: ravens
have been shown to retain
knowledge of past social
relationships for three
years, and chimpanzees can
remember how to solve a food-
gathering puzzle for three years.
They suggest that a long and
detailed memory may be useful
to fringe-lipped bats, allowing
them to recognise and exploit
prey animals that are rare or
seasonal, so aren’t encountered
for extended periods.
Jesús Rafael Hernández-
Montero at the ECOSUR San
Cristobal research centre in
Mexico is impressed by the
bats’ robust recall. “They get
this association in a very short
period of time, within 11 to
27 days of training,” he says.“And then they’re able to
remember that 4.2 years
later, so that’s quite amazing.”
He points out that, years
later, the bats also responded
to unrewarded ringtones from
their training. Generalising the
ringtone-food association may
reflect curiosity, perhaps making
them “more prone to explore
new cues”, he says, which would
potentially improve their
success at hunting.
In general, bats may be
encouraged to evolve long,
rich memories on account of
their biology and lifestyle, says
Hernández-Montero. They can
live for 20 years or more, group
together in complex societies
and navigate complicated
environments in complete
darkness – all traits aidedby the long-term logging of
social and environmental data.
Vladimir Pravosudov at the
University of Nevada, Reno,
isn’t surprised by the findings.
“It’s cool that they found [a long
memory in the bats],” he says.
But he also notes that “there’s
lots of data suggesting that a
lot of animals remember things
for a long time”.
One lesson emerging from
these and other recent findings
is that impressive cognitive
traits are actually widespread
across the animal tree of life,
says Pravosudov. Even fish
and invertebrates commonly
have lengthy memories and
substantial cognitive prowess. ❚A fringe-lipped bat
on Barro Colorado
Island, PanamaAnimal intelligenceJake BuehlerCHRISTIAN^ ZIEGLE
R/MINDENPICTU
RES/ALA
MY4.
Years that bats can remember a
sound they associate with foodBats can remember sounds
they haven’t heard for years
A ROBOT made of magnetic slime
with a custard-like consistency can
navigate narrow passages, grasp
objects and fix broken circuits. It
could be deployed inside the body
to perform tasks such as retrieving
objects swallowed by accident.
Elastic robots capable of
manipulating objects and fluid-
based robots that can navigate
tight spaces both already exist,
but versions combining both
properties are less common.
To address this, Li Zhang at the
Chinese University of Hong Kong
and his team mixed neodymium
magnet particles with borax, a
common detergent, and polyvinyl
alcohol, a kind of resin, to form a
slime that can be controlled by an
external magnetic field. They added
a silicon compound that coats the
magnetic particles to make them
non-toxic for use in people.
The robot was tested in various
scenarios, such as encapsulating
a swallowed battery in a model
stomach, grasping a piece of wire
and squeezing through millimetre-
sized gaps (Advanced Functional
Materials, doi.org/hpbj). The slime
appears to transition between tasks
easily and self-heal when cut up.
“You can first elongate it to a very
large extent so it looks like a liquid.
Then afterwards, you can roll it like
an octopus’ arm to carry something,”
says Zhang.
“They need to verify safety with
future trials, but it’s definitely a
sound approach,” says Pietro
Valdastri at the University of
Leeds in the UK. ❚TechnologyAlex WilkinsSlug-like slime
robot could crawl
through your bodyZH
AN
G^ E
T^ A
L.^ (
20
22
)
The slime robot
engulfing a batteryNew Scientist Video
See video of the slime robot and much more online
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