Seven Words to Know About Squirrels

With over 200 species spread across the continents of the Americas, Eurasia, and Africa, squirrels can be found in many parts of the world.  These rodents can range from the tiny African pygmy squirrel which is only five inches long to the Laotian giant flying squirrel which is the longest squirrel at four feet long. The heaviest species of squirrel is the Alpine marmot which weights between 11 and 18 pounds.  For those living in the United States, most are more familiar with medium sized squirrels like the Eastern and Western gray squirrels.  The Eastern gray squirrel has adapted to human settlements and is a common backyard feature of many urban and suburban locations.

The etymology of the word squirrel ultimately can be traced back to the Ancient Greek σκίουρος, (skiouros) meaning shadow-tailed.  The word first entered the English language in 1327.  Here are seven words anyone who loves to learn about squirrels should know.

Altricial

Altricial means to be born completely dependent.  The word altricial comes from the Latin alere, meaning “to nurse, to rear, or to nourish”.  Squirrels are born altricial and are completely dependent on their mother’s care for the first three months of life.

Four-week old Eastern Grey squirrel. Photo: Audrey, CC-BY

Four-week old Eastern Grey squirrel. Photo: Audrey, CC-BY

Caches

Squirrels are hoarders, known for stockpiling nuts and seeds for leaner months.  Squirrels save food for later months by creating caches.  These are often buried locations where a nut or seed is placed into a hole in the ground and then covered by soil.  Squirrels tend to either be “larder hoarders” which means they cache their food in one location that is vigorously defended against invaders.  “Scatterer hoarders” like the Eastern Grey Squirrel bury food in multiple caches.  Instead of one central location, seeds are hidden in locations all throughout the range of the individual squirrel.  These squirrels also engage in what has been termed “deceptive caching“.  Since up to a quarter of all hidden food is found by other squirrels, birds, and other hungry invaders, squirrels engage in the practice of pretending to bury a seed or nut to fool any onlookers.

Crepuscular

Animals that are most active at dawn and dusk are known as being crepuscular.   Crepuscular comes from the Latin word crepuscular meaning “twilight”.Many species of squirrels are crepuscular especially during the warmer seasons.  This allows squirrels to forage for food and engage in other activities during the coolest parts of the day.

Drey

The above ground nest that a tree or flying squirrel creates is called a drey (sometimes spelled dray).  Dreys are most commonly found in the forks of trees (ground squirrels tend to make their homes underground in burrows). Dreys are made of branches, leaves, and twigs.  Dreys are most obviously seen during winter on deciduous trees whose branches are bare of leaves.  Squirrel nests located inside trees are known as dens.

A drey located at the fork in a tree.

A drey located at the fork in a tree.

Hypermobilily

Have you ever seen a squirrel walk head first down a tree or paused along the trunk and stretch out its forelimbs while its hind legs are anchored to the tree?  Unlike many mammals, squirrels have amazing agility.  Known as hypermobility, squirrels are able to rotate their ankles 180.

Hypermobility gives this squirrel the ability to rotate its ankles in order to grasp the tree bark while descending the tree.

Hypermobility gives this squirrel the ability to rotate its ankles in order to grasp the tree bark while descending the tree. Photo: Micolo J, CC BY

Melanism

Some species of squirrels have evolved to exist in both open vegetative environments (like prairies) and dark forests.  Researchers have hypothesized that members of Easter Grey and Fox squirrels have evolved a mutation that results in black fur for those squirrels that exist in interior forests.  This black mutation allows squirrels to blend into the dark environments as a predator evasion adaption.  This adaptation is known as melanism.

Eastern Grey Squirrels. Image: Elizabeth Hunter.

Eastern Grey Squirrels. Image: Elizabeth Hunter.

Patagium

There are 44 known species of flying squirrels in the world. Despite the name, flying squirrels aren’t actually able to fly.  Instead, these squirrels glide through the air, aided by their patagium.  The patagium is a membranous structure that extends between the limbs that functions similar to a parachute in slowing down the descent of the squirrel, allowing it to control the direction of its glide through the air.

Ventral view of the patagium of the Laotian giant flying squirrel (Biswamoyopterus laoensis) Source: Sanamxay et al., 2013.

Ventral view of the patagium of the Laotian giant flying squirrel (Biswamoyopterus laoensis) Source: Sanamxay et al., 2013.

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