A wildlife photographer captured images of the rare penguin on a remote island in South Georgia in December 2019 and only recently released the photos. A king penguin "walked up straight to our direction in the middle of a chaos full of sea elephants and Antarctic fur seals, and thousands of other king penguins," the photographer from Belgium, Yves Adams wrote on an Instagram post. "How lucky could I be!"

At the time, Adams was leading a two-month photography expedition through the South Atlantic and had stopped on a South Georgia beach. While unpacking safety equipment, he saw a fluttering of penguins swimming toward the shore — one individual immediately caught his eye. 

"I'd never seen or heard of a yellow penguin before. There were 120,000 birds on that beach, and this was the only yellow one there," Adams told Kennedy News and Media. "We all went crazy when we realized. We dropped all the safety equipment and grabbed our cameras."

King penguins (Aptenodytes patagonicus), just like the closely related emperor penguins (Aptenodytes forsteri), typically adorn a black-and-white coat with a yellowish-gold dash of color on their collar. The yellow pigments are "unique to penguins," though not all species have them, according to the Australian Antarctic Program.

This particular penguin seems to have retained its yellow feathers but lost its dark ones, which are typically colored by a blackish brown pigment known as melanin.

Penguins with unusual plumage are relatively rare, and sometimes it can be difficult to identify the cause behind the rare colors just by looking at the penguins, according to the Australian Antarctic Program. Some unusual coloring can be due to injury, diet or disease, but many instances are due to mutations in the bird's genes. Such mutations can cause, for example, "melanistic" penguins whose typically white parts are black and "albinistic" penguins that don't have any melanin and thus are white.

Adams told Kennedy News that the yellow bird has a genetic condition known as leucism in which only some of the melanin is lost. 

Dee Boersma, a conservation biologist and professor at the University of Washington who was not a part of the expedition, agreed. "This penguin is lacking some pigment so it is [leucistic]," Boersma told Live Science in an email. "True albinos have lost all pigment." (Boersma said the bird has a brown head and so must have retained some of the pigment.)

Read the full article in Live Science.