The other day, walking down a tree-lined street, a couple of scientists were startled by a sudden crash and scramble at their feet. A squirrel had fallen from a tree! It quickly recovered and dashed away, back up the same tree trunk from which it had come. That never—or, almost never—happens. Why not? Cognitive scientists and biomechanics experts at the University of California, Berkeley, set out to answer this question by testing both the agility and decision making of wild fox squirrels living at the edge of their campus.

The results made the cover story in Science on August 6 with the title, “Acrobatic squirrels learn to leap and land on tree branches without falling”. The report begins thus:

“Every day, there are acrobatic extravaganzas going on above our heads. Squirrels navigate remarkably complex and unpredictable environments as they leap from branch to branch, and mistakes can be fatal. These feats require a complex combination of evolved biomechanical adaptations and learned behaviours. Hunt et al. characterized the integration of these features in a series of experiments with free-living fox squirrels (see the Perspective by Adolph and Young). They found that the squirrels’ remarkable and consistent success was due to a combination of learned impulse generation when assessing the balance between distance and branch flexibility and the addition of innovative leaps and landings in the face of increasingly difficult challenges.”

Regrettably they assumed that the complexities of this animal’s capability were due to “evolved biomechanical adaptions” but later admitted that they could not account for the origin of these mechanisms.

Squirrel parkour

The researchers discovered, too, that squirrels know parkour—the ability to bounce off a wall for extra oomph in a dangerous leap. They seem to be born with the ability to do it without having to learn all the complex moves needed. A combination of traits is necessary: a flexible body, good senses, strength, agility, rapid decision-making ability and instinct. Which traits are the most critical for success? Lack of any one of them could prove fatal. These requirements shape up to be an irreducibly complex set of skills.

In the experiments, the team gave the squirrels challenges that required calculating risks and rewards. To get to the nut, a squirrel had to negotiate a narrow flexible strip and then leap to a post. Squirrels instinctively knew whether the strip could support their weight and was stiff enough for the launch. If the strip was sufficiently stable, they would crawl out to the end and jump. If not, they would start their jump farther back with more energy. Sometimes they would “parkour” off the vertical wall to get to the post. If they overshot or undershot, they had a backup plan: they knew their claws could save them. They would grab the bar and flip over or under it and land on top—like a star gymnast. Most of the time, they nailed the landing with all four feet fitting on the tight platform provided. The scientists were amazed at their quick calculations.

“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 centre 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.”

This adds another specification: an excellent kinesthetic sense. The animal must know its body’s strengths and weaknesses, its position, and its current weight. If a mother squirrel is leaping while carrying a baby, it must calculate its resources without error each time.

A complex ability like leaping over a gap to a reward presupposes a set of specifications. Each specification is measurable: for a squirrel mass (m), needing to clear a gap of distance (d), launching from a platform with springiness (x), an engineer can calculate the force needed and test it with robotics. More variables can be specified for in-flight correction (parkour moves) and claw strength for grasping and swinging. The specifications are likely to get increasingly complicated when requirements for sensing and balance are considered. But this is science that is precise, measurable, and testable. It also has explanatory value: once the requirements are known, the set of causes necessary and sufficient to achieve them can be evaluated.

And the squirrels handle all these calculations instinctively with great aplomb.

The amazing spectacular squirrel tail

There is little doubt that the most beautiful and instantly recognisable physical characteristic of the squirrel is its tail. It serves as a sunshade; as a blanket in cold or stormy weather; as an expressive aid to communication; as a counterbalance in effecting marvellously quick turns; as an aerial rudder when its owner leaps from branch to branch, and as a parachute to soften the impact of occasional falls.

The very name “squirrel” comes from two Greek words, skia, meaning “shadow”, and oura, meaning “tail”.

Squirrels can unconsciously regulate the blood flow to the tail to aid in thermoregulation—or the control of the animal’s body temperature. A long tail, which has a large surface area per unit of length, tends to lose heat rapidly. In hot weather, the squirrel increases the amount of blood flow to the tail, dissipating more heat and helping it to cool off. In cold weather, the amount of blood flow to the tail is reduced, conserving more heat and helping the squirrel to stay warm.

Many species of squirrels, especially ground squirrels, live in areas where they are threatened by venomous snakes. One strategy that the squirrels have to protect themselves is tail flagging, which involves facing the snake directly, and waving the tail rapidly back and forth. At the same time, the squirrel is increasing the blood flow to the tail, causing it to heat up. Snakes such as rattlers and cobras hunt more by detecting heat than by sight. Tail flagging together with the heating of the tail causes the squirrel to look larger and more threatening to the snake.

Storing nuts

If you’ve ever watched a squirrel with a nut, you might have noticed that it turns it over and over in its paws whilst bobbing its head. That seems to be a way for them to judge the weight and other qualities of the nut they are holding, which suggests that information is useful for them in their subsequent stashing.

This behaviour drove Delgado and her colleagues at the University of California, Berkeley, to investigate whether squirrels were sorting the nuts somehow.

“Chunking” is a cognitive strategy in which humans and other animals organise information into manageable categories, similarly to subfolders on a computer. Fox squirrels can stockpile up to 10,000 nuts a year and can separate their caches by the types of nuts they are storing.

“This is the first demonstration of chunking in a scatter-hoarding animal, and also suggests that squirrels use flexible strategies to store food depending on how they acquire food,” said study lead author, Dr Mikel Delgado, along with psychology professor Dr Lucia Jacobs.

“Presumably, sophisticated caching techniques maximise the squirrels’ ability to remember where they have stored their most prized treats, while at the same time hiding them from potential pilferers,” the researchers said.

“Squirrels may use chunking the same way you put away your groceries. You might put fruit on one shelf and vegetables on another. Then, when you’re looking for an onion, you only have to look in one place, not every shelf in the kitchen,” said Dr Jacobs.

The researchers gave squirrels 16 nuts in rows of four: for instance, four almonds followed by four pecans, then hazelnuts and walnuts. They gave other squirrels the same 16 nuts but in a random order. Using hand-held GPS navigators, researchers mapped how the squirrels stored their caches of nuts.

They found that squirrels who foraged at a single location frequently organised their caches by nut species and would keep each category of nut separately. Squirrels that foraged in multiple locations deliberately avoided caching in areas where they had already buried nuts, rather than organising them by type.

Jacobs measured squirrels’ brains over the course of the year and found that there was a seasonality to the brain size: larger in the fall during nut storage, smaller the rest of the year. She believes that squirrels build a mental map of their nut caches, and that process makes their brains grow larger during this time.

Squirrel decisions

The moment a squirrel first encounters a tasty morsel of food, it has to make an important decision: Is it better to eat this now, or will it be more valuable in the future?

“A lot goes into answering that question,” says Amanda Robin, who studies squirrel behaviour at the University of California, Los Angeles.

Another incredible thing about squirrels is the fact that they actually know when they need to stash their food. For example, acorns that sprout late have a high-fat content, and they are ideal for storing for the winter months. Squirrels know this, and so they make sure to store these acorns for long-term for the winter while subsisting on less nutritious acorns in the warmer months. This shows forethought and awareness and illustrates that the squirrels know when they will need certain nuts more than others.

They understand the difference in variety, size, and weight of nut, as well as what they need to store and what they can eat. Squirrels are smarter than you realise!

In 2017, Pizza Ka Yee Chow, a squirrel researcher at Hokkaido University in Japan, put their memory to the test with a group (or, scurry) of eastern grey squirrels (Sciurus carolinensis), which are native to the eastern half of the United States and south-eastern pockets of Canada. Chow presented her squirrels with a tricky task: pressing levers to access big, juicy hazelnuts. The animals quickly finagled (tricked, or cheated) their way through, and Chow took the puzzle away. But even after nearly two years had passed, the same squirrels, which hadn’t seen the contraption in the interim, still knew how to nab the nuts.

They even proved handy when offered a modified puzzle that also relied on levers, but which looked completely different. After a brief moment of hesitation, the squirrels realised that even with this new challenge, the same logic applied.

Master manipulators

Even amongst their own kind, squirrels are master manipulators. When eastern grey squirrels forage in the presence of others, they’ll sometimes engage in what’s called deceptive caching. If it senses a hungry interloper, a squirrel will fake the act of burying a seed, all the while keeping the true prize tucked away in its mouth. A squirrel can get pretty elaborate with the ruse, making a big show of packing the hole with soil and leaf material, before bounding off to deposit the actual seed elsewhere. The second squirrel, of course, raids the decoy only to be disappointed.

“Up until the point where we found it in squirrels, this kind of tactical deception was thought to only occur in primates,” says Michael Steele, a squirrel expert at Wilkes University. “To discover it in [what people consider] a lowly rodent was pretty exciting.”

Squirrels may pale in comparison to their flying squirrel relatives, but even tree squirrels are equipped with extraordinary anatomical adaptations that enable them to clear ten-foot gaps between branches and stabilise on uneven surfaces. Grey squirrels’ hind legs, for instance, are exceptionally powerful and packed with muscles that can propel their light bodies forward over large distances. They’re also equipped with hyper-mobile ankles, allowing them to rotate their paws and grip onto surfaces in nearly any orientation. “Their ability to navigate through trees and balance so well is kind of a superpower,” Robin, a UCLA researcher, says.

Once more we have a creature that combines many agile traits to survive. If any one of these was missing, then its survival would be in jeopardy. How, too, did it know to store food in the winter months—an important decision which would suggest forethought? How could evolution anticipate an environment where there would be no food for the animal to eat and provide a solution in the squirrel’s genes for that eventuality?

The biblical testimony is clear. God created all things and, more significantly, sustains every form of life, particularly providing “meat in due season” for even the humble squirrel (Psa 145:15-16).