This story appears in the February 2018 issue of National Geographic magazine.

Squirrels aren’t natural city slickers. In 1856 the sight of one in a tree near New York’s city hall so shocked passersby that a newspaper published a report about the “unusual visitor.”

Around that time, the tree-dwelling rodents were being released in America’s urban areas to “create pockets of rural peace and calm,” says University of Pennsylvania historian Etienne Benson, who studied our relationship to squirrels over the course of five years.

Deciphering the Strange Behavior of Squirrels Squirrels are one of the most common animals found in urban and suburban areas, but many of their behaviors can go unnoticed. You may have seen squirrels burying nuts, but what you may not have noticed is just how organized their stash is. Scientists at UC Berkeley, however, spend a lot of time watching squirrels. They found that squirrels sort their stores by food type, and exhibit complex body language, even showing signs of frustration. In a less formal experiment, one video blogger captured squirrels' anxiety when presented with a figurine surrounded by food. In another test, it was the squirrel doing the capturing, making off with a camera baited with bread.

READ: Squirrels Gone Wild: Their Quirky Behaviors Explained

First they were introduced to Philadelphia, then to New Haven, Boston, and New York City. Park visitors were encouraged to feed them, and security guards ensured their safety. In the 1910s a Boy Scouts leader proclaimed that teaching children to feed squirrels could show the rewards of treating a weaker creature with compassion, says Benson.

By the early 20th century, though, America began to regret the hospitality it had shown squirrels. Cities had once been filled with animals—from horses pulling buggies to dairy cows and slaughterhouse livestock. By the 1950s those working animals had been moved to rural areas. Pets and wild animals such as birds and squirrels were all that remained of the urban animal kingdom.

Before long, the squirrels’ novelty waned, and they started to be seen as nuisances. By the 1970s many parks prohibited feeding the creatures. Today, says Benson, “people’s experiences with squirrels depend on their real estate investments.”