Pesto, the huge and beloved Australian penguin, is growing up and losing his fluffy feathers.

They grow up so fast: Pesto, the viral juvenile king penguin at Sea Life Aquarium in Melbourne in Australia, is starting to lose his baby feathers.

The beloved bird that became a global internet sensation earlier this year is starting to moult. The brown down covering his body falls off and he begins to grow black and white adult feathers.

In a recent video released by the aquarium, Pesto can be seen toddling around his enclosure as usual. But his once plump appearance now looks a little different, with his upper body still covered in brown down and his lower body covered in sleek white feathers. As eagle-eyed internet observers have noticed, he appears to be wearing shorts.

“We never know how they’re going to fledge,” says Jacinta Earley, an aquarist at Melbourne’s Sea Life Aquarium. National GeographicAllegra Rosenberg. “Sometimes it seems like they’re just wearing a fur vest. In other cases, it looks like they have a large mohawk running all over their body. It’s really fun and random.”

The full process will take about three to four weeks, and keepers expect Pesto to lose all his youth sometime in November.

Although his feathers are now changing, Pesto’s beak will remain pure black for the next two years until he reaches sexual maturity. It will then develop elongated orange spots on either side of the lower beak, which is characteristic of adults.

Pesto was born at the end of January, so he is about 9 months old. His birth was a big deal for the aquarium, which had not produced any king penguin chicks in 2023. He was also the only king penguin to hatch in 2024.

When he was born, Pesto weighed less than half a pound. But as he got older, he began to rapidly increase in size, eventually reaching 50 pounds. By comparison, adult king penguins typically weigh between 31 and 37 pounds. Pesto is Sea Life’s biggest chick in Melbourne.

In April, the aquarium put the pesto on public display. But it wasn’t until staff held a gender reveal party in September that the huge chick became a global celebrity.

Pesto is raised by a pair of foster parents named Tango and Hudson, as his biological father, Blake, is the oldest penguin in the aquarium and is probably too tired to raise the chick. But Blake is also the largest adult penguin in the aquarium, and his genetics may partly explain Pesto’s gigantic size. The huge baby also has a healthy appetite, eating 25 fish – blue whiting, rainbow trout and salmon – every day.

As Pesto grows, keepers expect him to lose weight. He will always be tall like his father, but Pesto will likely weigh around 33 pounds as an adult.

Molting is the main reason why king penguins lose weight as they get older. The process of shedding old feathers and growing new ones requires a lot of energy, so birds use up some of the fat stored under the skin.

King penguins usually moult between 10 and 12 months of age. Pesto’s timeline is sped up slightly, likely due to the abundance of food available to him in captivity, according to National Geographic.

In the wild, king penguin chicks usually molt only after their parents return to feed them in the spring. The chicks spend the winter fasting, so spring feeding gives them a much-needed boost in calories and allows them to build up the fat reserves needed for the energy-intensive metamorphosis.

Once king penguins have their adult feathers, they will be much better protected from the harsh sub-Antarctic elements. Adult king penguins have only four layers of feathers: three inner layers covered with down and an oily, waterproof outer layer.

These adaptations are less important in captivity, where the enclosures are climate controlled. But his new set of waterproof feathers will mean Pesto can finally swim with his many penguin friends and fans.

“His best friend is his father, Hudson,” according to an FAQ page created by the aquarium. “Aunt Queenie loves babysitting too. Other young birds like Honey and Sausage really like pesto.”

Even though he’s entering an awkward teenage phase, Pesto’s popularity has never wavered. Celebrities like Katy Perry and Olivia Rodrigo stopped by to meet the internet star in real life. Melbourne street artist Lucas Kasper has also painted a huge pesto mural in the city.

Pesto was visited by crowds of non-celebrities, including Millie Jacoby, a 25-year-old who had already come to see him twice by the end of September.

“We walked in and all we saw was this big fluffy penguin… and we just fell in love,” Jacoby tells BBC News’ Tiffany Turnbull. “He deserves the glory.”