(CNN)The Calgary Zoo in Canada is sending two giant pandas back to China due to a shortage of bamboo.
The zoo said in a statement that it usually flies in bamboo from China to feed the animals, but the Covid-19 pandemic had disrupted flights and caused delays in supplies.
The duo, named Er Shun and Da Mao, were supposed to stay in Canada until 2023 as part of a 10-year agreement with China, but the zoo decided to send them back early out of concern that delays could worsen if there's a second wave of coronavirus cases.
A panda's diet consists almost entirely of fresh bamboo, the Calgary Zoo said, and the animals typically eat about 40 kilograms (88 pounds) of it each day.
Much of the bamboo Er Shun and Da Mao ate before the pandemic was flown in directly to Calgary from China, but those flights have been canceled.
The zoo said it tried to find new bamboo suppliers to keep the pandas fed, but encountered several logistical issues. They also worry that these new supply lines could be disrupted at a moment's notice, leaving the pandas completely without food.
"We believe the best and safest place for Er Shun and Da Mao to be during these challenging and unprecedented times is where bamboo is abundant and easy to access," the president and CEO of the Calgary Zoo, Dr. Clément Lanthier, said in a statement. "This was an incredibly difficult decision to make but the health and well-being of the animals we love and care for always comes first."
Er Shun and Da Mao arrived in Canada in 2014 and spent five years at the Toronto Zoo before moving to Calgary in March 2018 with cubs Jia Panpan and Jia Yueyue, the Calgary Zoo said. Those cubs have been moved to China, CNN media partner CBC reported.
Lanthier told CBC that the zoo began the process to move the pandas a few weeks ago and hopes to have permits approved this week, though he would like to see the process expedited.
2013: China's panda diplomacy 02:29
Giant pandas are among some of the rarest animals on the planet, though efforts to preserve the species have shown some success in recent years. In 2016, the giant panda's status was upgraded from "endangered" to "vulnerable" by the International Union for Conservation of Nature. There are only an estimated 1,864 of them living in the wild, according to the World Wildlife Fund.
China has for years sent giant pandas abroad as a sign of friendship and cooperation between Beijing and other countries as part of a campaign known as "panda diplomacy," offering foreigners a chance to see these animals in person while also fostering ties between governments.
