What is molting, and who does it?

Molting is the fascinating process in which animals—like birds, reptiles, and even mammals—shed their old feathers, fur, skin, or shell to make way for new growth. It’s a bit like the biological version of when you get a new jacket after yours has worn down or no longer fits.

The process and signs of molting are unique from species to species. You might notice feathers askew, a variation in fur color, or a snake-shaped shed left behind. Read on to learn about the Aquarium animals that molt and how our team supports them during their transition.

Penguins

If you’ve ever spotted any of the penguins at the Aquarium looking scruffier and fluffier than their fellow colony mates, they might have been in the middle of a molt!

When they’re not molting, penguins have two layers of feathers, one fluffy layer closest to the body and one sleek external coat. This combination keeps them warm and waterproof in cold ocean waters. Feathers are so important to penguins that they spend much of their time on land preening them to ensure their coat retains maximum effectiveness.

But over time, their feathers start to wear down and need to be replaced—which is what molting is all about. Unlike some other species of birds that might lose and regrow feathers slowly over time, penguins experience a yearly “catastrophic molt,” replacing all their feathers at once. Before this happens, a penguin will increase their intake of fish, sometimes almost doubling their usual amount. This is because, in their natural habitat, they can’t hunt during the molt without their waterproof insulation, and bulking up allows the penguin to go for several weeks without needing to. During this time at the Aquarium, animal caretakers will give penguins a larger, stretchy ID bracelet since they may grow up to double their weight and size!

Once fully bulked, the penguin will stay on land, and their feathers fall away. The entire coat is replaced in two to three weeks, and the penguin is ready to swim once more. After undergoing their first molt, juvenile penguins will find themselves with a new adult feather pattern, while adults will regrow the same distinctive feather pattern year after year.

Atlantic Harbor Seals

A seal’s fur plays a different role than a penguin’s feathers. A thick layer of blubber keeps the seal warm, and the main

purpose of its fur is to protect its skin from injury and UV rays. The short hairs of a seal’s coat also make it hydrodynamic as it glides through the water. To maintain all of these helpful properties, a seal’s coat is replaced once a year in a molt.

Seals molt over about three weeks in the summer, usually in July or August. At the start of this process, you will notice the old, yellow-tinted fur in their coats start to stick up and fall out. At the same time, a coat of shiny new silver fur begins to replace it.

The seals will remain on land as much as possible to optimize temperature and blood flow to the skin for hair growth. This requires a lot of energy, and seals will spend a good deal of their time relaxing and sleeping as their bodies work overtime. Sometimes visitors notice this sleepy behavior and ask if the seals are okay, but our educators let them know not to worry, the seals are just molting.

California Sea Lions

The Aquarium is also home to California sea lions, a species in the same group as seals called pinnipeds (Latin for “fin-footed” or “flipper-footed”). If you were to touch a sea lion during their yearly molt, your hand would be covered in fur when you pulled it away!

Lobsters

Though it can take as little as 20 minutes for lobsters to shed their old shell, they spend significant time and energy preparing to molt and recovering from molting during their lifetimes. To help them prepare, our Animal Care team provides an enriched diet to ensure they’re getting key nutrients, like calcium and iodine, to support healthy molts.

Once the lobster’s old shell is gone, they take water into their tissue and increase in size – sometimes gaining up to 50% of their previous weight. Their new shell hardens over the next few weeks. To reduce stress as much as possible during this vulnerable period, we may move certain lobsters to a private area away from other lobsters and visitors.

Interestingly, after a molt, some lobsters change colors slightly. If it’s a significant change, we even update their ID photo in our database, like a new driver’s license photo.

Anacondas

Snakes are perhaps the most famous of molters due to the striking evidence the process leaves behind in the form of shed skin. Anacondas are one of the largest species of snakes on earth, and their discarded skins can sometimes be shed in a single piece, making for impressive specimens. For this to happen, the snake secretes fluids in between their old skin and a newly grown layer below. This loosens up the layer to be shed and takes a couple of weeks. When it’s time to dispose of the old skin, a snake will rub its head against a solid object until the skin

splits and peels. This happens fairly often among anacondas, depending on how fast the snake is growing. Babies, who are growing quickly, shed up to twice a month.

When you next visit the Aquarium, keep an eye out for animals molting! Someone will likely be going through the process!