“It’s very (energy) expensive to spawn,” says Trucchi. “They have to use a lot of their body fat reservoir, the subcutaneous dermal layer, all the energy stored before, to grow new feathers. It’s a big change for the little chick.”

Pesto is expected to lose weight rapidly over the next three weeks as he works hard to grow his adult feathers as well as his adult muscles, both of which he will need to swim and fend for himself.

Is pesto showing signs of penguin evolution?

King penguins are often confused with emperor penguinsbut they are actually their ancestors. A million years ago, a population of king penguins headed south and began to evolve into their larger cousins, the emperor penguins. Emperor penguins are one of the most hardy and cold-adapted animals on the planet, breeding on the Antarctic sea ice in the dead of winter.

To survive, they developed defenses against the cold: their body temperature rose, they became taller and rounder, reducing their volume-to-surface ratio to lose less heat from the body. (That’s why they can’t be kept effectively in captivity, Wienecke says. Unlike kings, which can hang out comfortably in refrigerated habitats kept between 32° and 50° F, emperors’ habitats would have to be expensively kept below freezing.)

“There are a lot of these adaptations that had to occur at some point, and that could be due to what we call permanent genetic variation,” explains Trucchi. “These variations could have been in the ancestral king penguin population, or they could be the result of new mutations occurring at random and then being selected for.”