(CNN) — Yosemite, Yellowstone, Grand Canyon. These are the stars of the United States' national parks system, and with good reason.

Often called "America's Best Idea," the creation of national parks in the United States launched a worldwide movement to protect the Earth's natural treasures.

be very busy during These headliner national parks would typicallybe very busy during National Park Week , going on now through April 26. (The National Park Service welcomed more than 327 million visitors last year, a 2.9% increase from 2018, and the third highest number since record keeping began in 1904.)

But the coronavirus pandemic has shut down many of the most popular national parks, creating a forced experiment: What happens when animals who make their homes in these protected space have (mostly) free rein of the park grounds?

"With Yosemite and other parks closed to tourists, wildlife is coming out of hiding, and indeed, even thriving in our absence, reclaiming some of the places that have been dominated by human activity for decades," said Beth Pratt, National Wildlife Federation's regional executive director for California.

"With threats like vehicle collisions or being harassed for a selfie largely eliminated, the coyotes are trotting through Camp Curry hunting mice, and the black bears [are] wandering around a mostly empty Yosemite Village," said Pratt, who was vice president/CFO at the nonprofit Yosemite Conservancy for 10 years and still lives near the park.

It shows "that even in our best protected places on the planet -- our national parks -- wildlife still get impacted by us humans," Pratt continued.

"More than 400 bears have been hit by cars in Yosemite since 1995. That the animals seem to be enjoying this vacation from us is a good reminder that when the parks do reopen, let's be kinder and more respectful to the wildlife who call Yosemite and other parks home."

National parks were created during wartime

A herd of bison are seen in Hayden Valley at Yellowstone National Park. Avalon/Universal Images Group Editorial/Getty Images

This isn't the first time the US government has taken measures to protect nature during a human crisis.

President Abraham Lincoln and Congress protected parts of what is now Yosemite during the throes of the Civil War, with the passage and signing of the Yosemite Land Grant of 1864. It didn't become a national park until 1890.

Yellowstone was the world's first national park, created in 1872, and it wasn't controversial because it was so far away from where many people lived at the time.

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Most members of Congress didn't oppose the legislation because they hadn't seen the land, now-retired Yellowstone National Park historian Lee Whittlesey told CNN Travel during a 2016 interview about the 100th anniversary of the National Park Service.

The federal park legislation was just a political answer to a territorial argument. Meant to be a state park, Yellowstone land was in three territories.

"There was an immediate argument between Montana and Wyoming newspapers about who would get the park," Whittlesey said. "That is why Congress made it a federal park."

Lucky us.

Proof that nature is good for us

The view of the South Rim of the Grand Canyon is spectacular. RHONA WISE/AFP/AFP/Getty Images

There's no doubt that fans of the national parks will want to return to hike, picnic, camp and marvel at the views when they reopen. Nature is good for us, and studies back that up.

In a study released in early April, researchers found children who felt connected to nature -- described as feeling pleasure when hearing nature sounds and seeing animals and wildflowers -- engaged in actions that helped other people. They also recycled, saved water and cared for the environment in other ways.

Adults do better in nature, too. People who take walks in nature report less repetitive negative thoughts, according to a 2015 study.

But we need to take care of our natural treasures -- and it's not just the wildlife humans should be more thoughtful of when parks reopen.

When the federal government shut down from December 22, 2018 to January 25, 2019, the gates to many national parks were left open and irresponsible visitors created lasting damage.

Toilets overflowed, trash piled up and there was damage caused at Joshua Tree National Park , among other national parks, during the shutdown.

To be sure, there's only so much maintenance NPS staff can do to repair the more recent damage. They also face a $12 billion maintenance backlog that money, not just time, will heal.

The parks are for us and future generations

Summer in Acadia National Park in Maine is lovely. National Park Service

Conservation and current enjoyment of the parks, as stated in the 1916 legislation establishing the creation of the park service, should be "in such manner and by such means as will leave them unimpaired for the enjoyment of future generations."

The creators of the park service wanted us, as those future generations, to be caretakers -- not exploiters -- of our protected national resources.

It's possible that the closed parks will reopen before parks and their surrounding communities -- which often have limited medical facilities -- have time to hire their seasonal workers, said Phil Francis, chair of the Coalition to Protect America's National Parks.

"Visitors should consider that if they go to a popular park soon after reopening, they could find very crowded conditions."

"The NPS will certainly appreciate visitors who obey park rules and regulations," Francis said. "If restrooms are closed, please compensate for that before you arrive. Consider public hygiene. "

"Take out the trash you generate -- pack it in, pack it out -- and follow leave no trace principles," he said. "If garbage cans are full, take it with you and do not leave your trash beside overflowing garbage cans.

"Visitors can help by not trashing the park or damaging park facilities and resources."

Writer and historian Wallace Stegner called America' national parks "the best idea we ever had. Absolutely American, absolutely democratic, they reflect us at our best rather than our worst."

Let's bring our best selves when we return to visit these national treasures.

Most popular National Parks (62 total)

Great Smoky Mountains is the most popular national park. Shutterstock

Most popular National Park Service sites (419 total)

Golden Gate National Recreation Area is the most popular NPS site. Shutterstock

1. Golden Gate National Recreation Area (CA): 15 million visits

2. Blue Ridge Parkway (NC/VA): 14.9 million visits

4. Gateway National Recreation Area (NY/NJ): 9.4 million visits

5. Lincoln Memorial (DC): 7.8 million visits

6. George Washington Memorial Parkway: 7.5 million visits

7. Lake Mead National Recreation Area (AZ/NV): 7.5 million visits

8. Natchez Trace Parkway (AL/MS/TN): 6.3 million visits