Leaping squirrels! Parkour is one of their many feats of agility
Robots could learn from how squirrels assess their ability to leap and
land successfully

Date:
August 5, 2021
Source:
University of California - Berkeley
Summary:
Biologists tested free-ranging squirrels to determine how quickly
they adapt to the bendiness of their launching branch in order to
successfully land. The squirrels learned within a few trials to
leap no matter how bendy, but have a failsafe to stick the landing:
claws. They also innovated, bounding off vertical surfaces to
extend their range, just as parkouring humans. Incorporating such
control could improve robot agility.



FULL STORY ========================================================================== Videos of squirrels leaping from bendy branches across impossibly large
gaps, parkouring off walls, scrambling to recover from tricky landings.


==========================================================================
Just more YouTube content documenting the crazy antics of squirrels
hell-bent on reaching peanuts? No, these videos are part of a research
study to understand the split-second decisions squirrels make routinely
as they race through the tree canopy, jumping from branch to branch,
using skills honed to elude deadly predators.

The payoff to understanding how squirrels learn the limits of their
agility could be robots with better control to nimbly move through
varied landscapes, such as the rubble of a collapsed building in search
of survivors or to quickly access an environmental threat.

Biologists like Robert Full at the University of California, Berkeley,
have shown over the last few decades how animals like geckos, cockroaches
and squirrels physically move and how their bodies and limbs help
them in sticky situations -- all of which have been applied to making
more agile robots. But now they are tackling a harder problem: How do
animals decide whether or not to take a leap? How do they assess their biomechanical abilities to know whether they can stick the landing?
"I see this as the next frontier: How are the decisions of movement
shaped by our body? This is made far more challenging, because you also
must assess your environment," said Full, a professor of integrative
biology. "That's an important fundamental biology question. Fortunately,
now we can understand how to embody control and explain innovation by
creating physical models, like the most agile smart robots ever built."
In a paper appearing this week in the journal Science, Full and former UC Berkeley doctoral student Nathaniel Hunt, now an assistant professor of biomechanics at the University of Nebraska, Omaha, report on their most
recent experiments on free-ranging squirrels, quantifying how they learn
to leap from different types of launching pads -- some bendy, some not --
in just a few attempts, how they change their body orientation in midair
based on the quality of their launch, and how they alter their landing maneuvers in real-time, depending on the stability of the final perch.



==========================================================================
"As a model organism to understand the biological limits of balance
and agility, I would argue that squirrels are second to none," Hunt
said. "If we try to understand how squirrels do this, then we may
discover general principles of high performance locomotion in the canopy
and other complex terrains that apply to the movements of other animals
and robots." The experiments were conducted in a eucalyptus grove on
the UC Berkeley campus, where Hunt enticed fox squirrels that roam the
campus into sketchy situations where they had to decide whether to leap
for a peanut or let it go.

Hunt and Full found that, as expected, the flimsier or more compliant the branch from which squirrels have to leap, the more cautious they are. But
it took squirrels just a few attempts to adjust to different compliances.

"When they leap across a gap, they decide where to take off based on a
tradeoff between branch flexibility and the size of the gap they must
leap," Hunt said.

"And when they encounter a branch with novel mechanical properties,
they learn to adjust their launching mechanics in just a few jumps. This behavioral flexibility that adapts to the mechanics and geometry of
leaping and landing structures is important to accurately leaping
across a gap to land on a small target." But they don't balance the
bendiness of the launching branch and the gap distance equally. In fact,
the compliance of the branch was six times more critical than the gap
distance in deciding whether to jump.



==========================================================================
This may be because squirrels know that their sharp claws will save
them if they miscalculate. Their claws are so failproof, Hunt said,
that none of the squirrels ever fell, despite wobbly leaps and over-
or undershot landings.

"They're not always going to have their best performance -- they just
have to be good enough," he said. "They have redundancy. So, if they
miss, they don't hit their center of mass right on the landing perch,
they're amazing at being able to grab onto it. They'll swing underneath, they'll swing over the top.

They just don't fall." That's where exploration and innovation come
into play as squirrels search for the best leaping strategy.

"If they leap into the air with too much speed or too little speed, they
can use a variety of landing maneuvers to compensate," Hunt said. "If they
jump too far, they roll forward around the branch. If they jump short,
they will land with their front legs and swing underneath before pulling themselves up on top of the perch. This combination of adaptive planning behaviors, learning control and reactive stabilizing maneuvers helps
them move quickly through the branches without falling." One unsuspected innovation was that during tricky jumps, squirrels would often reorient
their bodies to push off a vertical surface, like in human parkour,
to adjust their speed and insure a better landing. Parkour is a sport
in which people leap, vault, swing or use other movements to quickly
traverse obstacles without the use of equipment.

Full and Hunt continue to explore the interaction between biomechanical abilities and cognition as squirrels learn new gap-leaping strategies.

Co-authors of the paper are former UC Berkeley psychology graduate student
Judy Jinn and Lucia Jacobs, a UC Berkeley professor of psychology and
an expert on animal cognition. Full and Jacobs, who operates a Squirrel
School at UC Berkeley, are part of a multi-university consortium funded
by the Army Research Office (ARO) to model the cognition and decision
processes in squirrels to one day create the world's first robot with
squirrel capabilities.

The current work was supported by ARO, the National Science Foundation
and the National Institutes of Health.

========================================================================== Story Source: Materials provided by
University_of_California_-_Berkeley. Original written by Robert
Sanders. Note: Content may be edited for style and length.


========================================================================== Related Multimedia:
* YouTube_video:_Can_'squirrelly'_skills_be_built_into_robots? ========================================================================== Journal Reference:
1. Nathaniel H. Hunt, Judy Jinn, Lucia F. Jacobs, Robert
J. Full. Acrobatic
squirrels learn to leap and land on tree branches without falling.

Science, 2021; 373 (6555): 697 DOI: 10.1126/science.abe5753 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/08/210805141121.htm

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