From gray squirrels to flying squirrels there are more than 300 species of squirrels worldwide. For Squirrel Appreciation Day here's a look at some of the amazing things squirrels do and are.

They're problem solvers

A University of Exeter study has shown that gray squirrels are fast learners capable of adapting tactics to improve efficiency in locating food.

To test the animals' intelligence and mental flexibility researchers invented a task involving a box with 12 sunken wells, four of which were hollow. Of the four, two contained hidden hazelnuts. The hazelnuts were placed in the wells diagonally across from each other, meaning that the least efficient way for the squirrels to locate the food was to check each well in a clockwise or counter-clockwise sequence, and the most effective was an "integrative" approach where squirrels checked only the two diagonal wells that contained food, ignoring the two empty wells.

The five squirrels in the study were given training prior to the task so they were proficient at using their paws or teeth to peel back the layer of paper hiding a nut inside the wells.

All of them showed improvement over successive attempts with the box, becoming more efficient in adjusting their behavior to adapt to the task.

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They can lie

Researchers monitoring gray squirrels in a 2008 study found the animals engaged in tactical deception. When a squirrel thought it was being watched by other squirrels it would dig a fake hole and pretend to deposit a nut into it, but instead tucked the nut into their cheek and waited to bury it elsewhere.

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They have a fantastic dental plan

The four front teeth in a squirrel's mouth never stop growing, which explains the squirrel's ability to cut through hard surfaces like nut shells and bark without grinding their cutting teeth away.

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That magnificent tail

A squirrel's tail performs an array of essential functions. It's used as:

A balance in climbing and racing along branches high in the treetops,

A signal to other squirrels about potential dangers in the neighborhood,

An umbrella to shield the rest of the squirrel from rain,

A wrap-around blanket in cold weather,

A rudder when swimming.

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They can fly

Well, squirrels can't really fly. But flying squirrels are able to glide more than 150 feet at a time thanks to the flaps of skin stretching along their sides between their front and back legs. Non-flying species, like the gray squirrel, have been measured making horizontal leaps of nearly 30 feet.

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They can run down trees

Most animals cannot climb head-first down a tree. Squirrels can because they can rotate the rear ankles 180 degrees. That allows them to run their rear paws completely around to grip the tree trunk behind them.

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That amazing sense of smell

Gray squirrels have been observed finding food buried under a foot of snow and a couple inches of soil, and not only food that they buried themselves.

Following their sense of smell, squirrels regularly locate food cached by other squirrels. Some researchers have documented squirrels losing as much as 25 percent of their stash to other squirrels.

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They still miss some

Despite their sense of smell, squirrels do not recover all the buried nuts in any given area. Some of those nuts spout and grow into trees, rejuvenating and spreading the nut tree population across the forest.

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They also spread mushrooms

Above-ground mushrooms spread their spores through the air, but those growing underground, like truffles, need animals like squirrels to eat the fungi and spread the spores in their scat.

All squirrels in Pennsylvania include fungi in their diets, particularly flying squirrels.

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They're great company

Try doing anything in a Pennsylvania woodland that requires periods of quiet, like deer hunting, and within minutes that woodland will be swarming with noisy squirrels darting through the leaves. It seems like our desire for quiet somehow acts as a magnet for squirrels. The true reason for all that squirrel activity lies in the abundance of squirrels in nearly every woodland across Pennsylvania and the tendency among those squirrels to resume normal activity a few minutes after we settle in and remain quiet.

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They're fun at the bird feeders

Many backyard birders view squirrels as their arch-enemies at their bird feeders, chasing off and threatening the birds, scarfing down all the prime seeds, scattering the seeds they don't want and, in the process, destroying the feeders.

Others welcome the squirrels as acrobatic clowns that provide hours of entertainment, as they work to solve problems like getting past every barrier that humans have come up with to keep them away from the feeders or dealing with devices meant to distract the squirrels like corn cob whirly-gigs.

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There are so many different species of them

More than 300 species of squirrels inhabit different parts of the world, ranging from the tiny African pygmy squirrel at just 5 inches nose to tail to the Indian giant squirrel measuring about 3 feet in length.

There are 5 species in Pennsylvania: gray, fox, red, northern flying squirrel and southern flying squirrel.

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They can be white

Albino squirrels can occur in any species but are most common in the gray squirrel species. Albinism has been observed in the red squirrel population near Old Main on Penn State's University Park campus.

White squirrels, lacking the red eyes of true albinos, are the result of a genetic variation known as leucism. The variation produces a partial loss of pigmentation in the fur of the animal.

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They can be black

The black squirrel is a color variation in the eastern gray squirrel. It is not uncommon across the northern tier of Pennsylvania. Easily observed populations exist in and around Milton and Little Pine state parks.

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They're prolific

Gray, fox and red squirrels are mating now. Pregnant females will produce litters of one to eight in 45 days or so, and the pups will be weaned within two months. The squirrels will breed again in June through September.

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They can be celebrated

Several North American towns have labeled themselves the "home of the white squirrel," including Olney, Illinois, which imposes a $750 fine on anyone killing an all-white squirrel and residents may not let their cats run loose outdoors; Marionville, Missouri; Brevard, North Carolina, which holds an annual White Squirrel Festival; Kenton, Tennessee; and Exeter, Ontario, Canada.

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And sometimes, not so celebrated

According to website Cyber Squirrel 1, which has compiled every public record of animals disrupting power services since 1987, squirrels have caused nearly twice as many disruptions as any other animals: squirrels, 1,228 disruptions; birds, 635; snakes, 116; raccoons, 114; rats, 52; cats, 26; martens, 25; jellyfish, 13; and monkeys, 12.

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