JOHN YANG: For many, it's a bittersweet farewell.

The giant pandas at the Smithsonian's National Zoo in Washington D.C. are heading home amid rising tensions between the United States and China.

But zoo officials hope it's just a pause and panda diplomacy and not the end of it.

Somersaults in the snow.

A first birthday party.

Simply eating a piece of bamboo.

Whether adorable or mundane, zoo visitors have been delighted by virtually everything that giant pandas have done since their first tumbles on U.S. soil more than five decades ago.

It was in 1972 that then-First Lady Pat Nixon welcome the furry tokens of goodwill from the Chinese government.

The gesture was sparked by a remark she made during President Richard Nixon's historic trip to China earlier that year, about her fondness for the rare species.

PAT NIXON, Former First Lady of the United States: Here at the National Zoo, they will be enjoyed by the millions of people who come from across the country to visit the nation's capitol each year.

I noticed Dr. Ripley is wearing a panda tie.

And I have my candle here now have you know, and I think pandemonium is going to break out right here at the zoo.

JOHN YANG: And did it ever.

Americans began a love affair with giant pandas leading to decades of scientific collaboration with China.

The original pandas Ling-Ling and Hsing-Hsing were gifts after they died in the 1990s with no surviving offspring, China began loaning more panda pairs for a fee.

Political reporter Michael Schaffer spoke with Ali Rogin about China's high price tag for providing pandas.

MICHAEL SHAFFER, POLITICO: China had a pretty lucrative business going and renting out its bears and rent a bear to zoos in rich countries for a lot of money.

And so the deal was with the two replacement behaviors, that they would come for 10 years, it would be $10 million, a million bucks a year.

And any cub that these bears produced would remain the property of the Chinese organization, the wildlife organization that sponsored this.

In the years since those the replacement rental pandas showed up.

American Chinese relations have gotten a lot tougher.

JOHN YANG: The first pair of replacements arrived in 2000.

And over the years produced for cubs that survived captivating crowds and earning legions of devotees.

JENNIFER SWANSON: Ever since the pandas came to Washington, I've made kind of a periodic trek here to see them.

And I just think it's really just it's so sad that they are all going to be leaving at the same time.

PAMELA WHITTED: Big panda fan.

Been in DC for 23 years now.

So, visited them many times in the baby's born over the years and it's really, really sad heartbreaking to see them go back to China and hopefully we can work something out the future for more pandas.

JOHN YANG: There are currently three pandas at the zoo, Mei Xiang, Tian Tian and their three year old cub Xiao Qi Ji to prepare them for the return to China's zookeepers are doing crate training exercises, using honey flavored water as a reward.

Sometime in the next two weeks, FedEx will transport them to Chengdu China a 19-hour journey.

BRANDIE SMITH, Director, Smithsonian's National Zoo: Their departure is something we have been prepared for, you know, our entire lives her entire career with them.

JOHN YANG: National zoo director Brandie Smith is a former panda curator.

BRANDIE SMITH: Right now we are so focused on making sure that these pandas are returned to China and they return you know, happily and safely.

But I can't see beyond that.

I know these animals.

I know them as individuals, they mean so much to me, and I'm really going to miss them.

JOHN YANG: She says the pandemonium has real benefits.

BRANDIE SMITH: People won't conserve what they don't care about.

People have to care to conserve.

And so for me, it's been so important to teach people to care about these animals to want to conserve these animals, but also to feel good about it.

There's a joy in this, and there's also a success.

JOHN YANG: The giant panda was taken off the endangered species list in 2016, but is still considered vulnerable to extinction.

The number of pandas under human care worldwide has gone from 100 in 1980 to more than 600 in 2020 and now it's estimated there are more than 1,800 pandas in their natural habitat in China.

As U.S. Chinese tensions mount the future of panda diplomacy remains an open and complicated question.

Georgetown University professor Dennis Wilder was a China specialist with the CIA and the National Security Council.

DENNIS WILDER, Georgetown University: The Chinese are angry with us.

They're angry over the semiconductor restrictions, the number of sanctions that the Biden administration has placed on Chinese individuals.

Problems China is have now getting visas to the United States.

So it could well be possible that they're trying to send a signal.

JOHN YANG: But zoo officials are optimistic.

They're spending more than $2 million to upgrade the soon to be vacant panda enclosure.