After spending the winter north of the sea ice, chinstraps return in late October or early November to their nest sites, usually with the same breeding partners. These colonies are on the rocky, ice-free coasts of the South Sandwich Islands, South Shetland Islands, and Antarctic continent.
The sheer number of birds in the colonies is astounding. The largest colony, on the uninhabited South Sandwich island of Zavodovski, hosts some 1.2 million breeding pairs. Baily Head in the South Shetland Islands is home to more than 100,000 pairs.
Breeding and nesting
A female chinstrap typically will lay two eggs in a circular nest made from stones. The parents share egg-sitting duties, each spending several days on the nest before a shift change. After about 37 days, the chicks hatch. They spend another few weeks in the nest, then waddle into a crèche, where the fluffy, gray juveniles are cared for communally. At around two months old, they get their adult feathers and are able to head to sea.
In the water, where they feed primarily on krill, the penguins’ main predator is the leopard seal. On land, chinstraps face threats from skuas, giant petrels, and other birds that steal the penguins’ eggs and attack chicks, as well as a more unusual threat: volcanic activity. An ill-timed eruption in 2016 on Zavodovski Island covered much of the colony in ash as the birds were undergoing their annual molt. During molt, when they lose their waterproof feathers, they are land-locked and can’t go in the sea until their feathers regrow.
Chinstrap penguin numbers increased in the mid-20th century, attributed by some to the rebound of krill from centuries of seal and whale hunting. Today, some populations are declining, though not precipitously. Restrictions are in place to keep tourists from approaching breeding birds too closely.