Being both land and sea animals, penguins face a variety of predators.
On land, Skuas (remember them, the rodents of Antarctica), Kelp Gulls, and Snowy Sheathbills threaten the penguins by carrying off the eggs or the young. Part of the reason we, as visitors to Antarctica, have to stay far enough away from the penguins is so that they don’t get distracted by our presence and lose an egg to a skua.
Leopard seals are threats in the sea. They have a great big mouth and rip apart anything smaller than them. They play with the penguins while chasing them, trying to turn them inside out. For more on seals, visit this post.
In these photos, we were lucky to come upon a leopard seal ripping apart something that wasn’t a penguin. We speculated that it was a Crabeater seal pup. The rib cage is evident. A penguin would float but in this case the leopard seal had to keep diving down to bring the carcass up.
All penguins are protected from hunting and egg collection on Antarctica so humans (theoretically) are not a threat to them.