Isla Martillo, a small island in the Beagle Channel near Estancia Harberton, hosts one of the few Magellanic penguin colonies accessible from Ushuaia. A smaller and growing number of Gentoo penguins has also established itself here in recent years. Visits are run exclusively by the Harberton estancia, which holds the concession, and landing is permitted only for small groups accompanied by a naturalist guide.
The colony is active from October through March. During breeding season (November to January), the penguins are incubating eggs or raising chicks and the island is extraordinary — adults shuffle back and forth to the shoreline while chicks wait in the burrows. Outside breeding season, the birds are present but less numerous.
Access is by boat from either Ushuaia (combined boat trip) or from the Harberton estancia dock. The landing on Martillo is a wet landing on a pebble beach; rubber boots or waterproof shoes are advisable. It is one of the most affecting wildlife experiences available from Ushuaia, with no fencing between visitors and birds.