Giant pandas en route to the National Zoo in Washington, D.C.

A pair of three-year-old giant pandas arrived at Washington Dulles International Airport Tuesday morning as part of China’s panda conservation program. The pandas, named Bao Li and Qing Bao, left Chengdu, China, on Monday and are bound for the National Zoo in the United States’ capital. Bao Li’s mother was born at the National Zoo in 2013. The zoo was scheduled to be closed Tuesday as the pandas were moved into their new home.

What is the history of the panda program? China sent the National Zoo pandas for the first time in 1972 as a symbol of international diplomacy and trade relations between the countries, according to the Congressional Research Service. Pandas typically return to China after they reach old age and any cubs born during their loan accompany their parents. Last year, Mei Xiang, Tian Tian, and their cub Xiao Qi Ji left Washington to return to China after the breeding pair spent 23 years in the United States. The original bears are the grandparents of the incoming panda, Bao Li.

After the bears in Washington left last year, Zoo Atlanta was the only American zoo to have pandas. Those bears, named Lun Lun, Yang Yang, Ya Lun, and Xi Lun returned to China last week. China loans panda bears to more than a dozen countries worldwide

Dig deeper: Listen to Mary Reichard’s report on The World and Everything in It podcast about Biden’s foreign policy regarding China.