DENVER ZOO, Colo. (KDVR) — As cases of the Highly Pathogenic Avian Influenza continue to pop up across the U.S., the Denver Zoo has had to quarantine its birds inside.

On March 24, Colorado Parks and Wildlife confirmed the first case of the avian flu in Colorado. Since then, the Denver Zoo has had to immediately move all its birds to a safe indoor area to avoid infection.

On Sunday, the zoo tweeted out a video showing how keepers have adapted to taking care of the birds while they remain inside. In order to help the grey-crowned cranes continue to exercise, the keepers use the hall of their animal hospital as a flight path for the birds to soar.

According to the tweet, “It’s one of many ways our keepers ensure our birds receive the best possible care while inside!”

The avian flu has affected more than 1.4 million birds in Colorado and more than 37 million birds nationwide. Gov. Jared Polis enacted a verbal state of emergency after a Delta County inmate tested positive for the flu on April 28.

Once the avian flu is detected in a facility, all the birds must be euthanized. The fast-spreading virus can cause sudden death, lack of appetite, sneezing and swelling in birds that are infected.

Although guests at the Denver Zoo are not able to visit with the penguins, cranes, or eagles, they can be reassured that their winged friends are getting the best care under difficult circumstances. The zoo will continue to update the status of the quarantine on its website.