Although penguins can’t fly, they still need feathers. Without them, the birds risk disease and even death, which is why researchers are concerned about the recent reappearance of a rare disorder causing the feathers of young penguins to fall out.

Known as feather-loss disorder, the condition was first seen in 2006 in penguin chicks housed at a captive facility in South Africa. A year later, several cases were observed in wild Magellanic penguin chicks along the coast of Argentina.

Now, seven years after the last outbreak, feather-loss disorder has reemerged, this time in penguins on the Antarctic Peninsula, researchers report in the journal Antarctic Science. In January, they spotted two chicks (one of which is pictured above) in the Hope Bay Adélie penguin colony that were missing large patches of feathers. One chick was later found dead, and the other has disappeared and is presumed to have perished.

The fact that no other cases were observed in the colony of 14,000 penguins suggests that feather-loss disorder is not easily transmitted between individuals. Still, the cause of the disease and how it spreads remain mysteries that scientists are racing to solve.