Penguin Life Cycle on Martillo Island: Nesting, Chicks and Molting

The penguin season on Martillo Island is a sequence, not a single spectacle. Magellanic and Gentoo Penguins return to breed in spring, establish nests, incubate eggs, raise chicks and prepare young birds for life at sea. By late summer, fledging and molt change both the birds’ appearance and the colony’s activity. Exact timing varies by species, year and individual nest.

This article explains what each life-cycle phase may look like without promising eggs or chicks on a particular departure.

 

For how to reach the island and which tours operate, read our penguin tour guide from Ushuaia.

 

Spring: adults return and nesting begins

Magellanic Penguins reclaim burrows

Magellanic Penguins spend much of the nonbreeding period at sea and return to coastal colonies in austral spring. At Martillo Island, they use burrows or protected scrapes in soil and vegetation. Returning adults may repair an old burrow, compete for a site, call to a mate and move nest material.

A visitor may notice birds disappearing below ground, standing at burrow entrances or following worn paths between colony and shore. A quiet-looking patch of earth may contain an active nest, which is one reason visitors must remain on the designated route.

 

 

Gentoo Penguins build open nests

Gentoos remain associated with Martillo Island year-round more than the migratory Magellanics do. Their breeding sites are open, raised nest mounds built from stones and available vegetation. Pairs repeatedly add or reposition material, making nest maintenance easier to see from a respectful distance.

Peer-reviewed work at Martillo has documented a Gentoo breeding season beginning around September, with chicks fledging by February in the studied cycle. More recent research shows the timing can shift between years, so calendar dates should be treated as a pattern rather than an appointment.

Incubation: why an occupied nest may look inactive

Both parents share incubation and foraging responsibilities. One adult may remain almost motionless over eggs while the partner feeds at sea. The bird’s belly conceals the eggs, and visitors should not expect or attempt to see them.

Magellanic Penguins commonly lay two eggs; Gentoos also commonly lay two. “Two eggs” does not mean that every pair will hatch or raise two chicks. Weather, food availability, predation, experience and individual condition all influence breeding success.

Signs of incubation include a low, settled posture, careful turning movements and a partner returning to exchange duties. None of these justify leaving a path or approaching a nest for confirmation.

My visitor rule: if a nest seems visually unrewarding, that is not permission to get closer. A calm incubating bird is evidence that the viewing system is working.

Early summer: chicks hatch and require constant care

Newly hatched chicks have soft down rather than waterproof feathers. They depend on adults for warmth, protection and food delivered after foraging trips. At first, a chick may be visible only when an adult stands or shifts position.

Magellanic chicks remain connected to burrows and their immediate surroundings. Gentoo chicks begin at open nests and later become more mobile. Adults returning from the water may pause, call and navigate through the colony before reaching their own young. Penguin colonies are noisy because vocal recognition helps birds find partners and chicks among thousands of neighbors.

Midsummer: growth, crèches and practice

As chicks grow, their demand for food rises and their down becomes conspicuous. Gentoo chicks may form loose groups called crèches after leaving constant nest guarding. Magellanic chicks also spend more time outside burrows as they develop.

Visitors may see wing stretching, preening, short runs, begging calls and young birds near the shoreline. These behaviors are preparation, not a performance. A chick approaching a path does not mean it should be touched, surrounded or encouraged.

Food availability affects growth and timing. That is why one visit can show small downy chicks and another older juveniles with sleeker plumage even within the same broad month.

 

 

Fledging: the change that makes the sea possible

Before a young penguin can leave for sea, it must replace insulating down with waterproof juvenile feathers. A fledgling may look gray or brownish and lack the sharp adult pattern. The transition can make identification harder: young Magellanic Penguins do not yet show the adult’s crisp double chest band.

Going to sea is not a ceremonial one-day event across the colony. Individuals enter at different stages, test the shoreline and depart according to development and conditions. By late summer, the number and appearance of young birds can change quickly.

Molting: why a healthy penguin may look untidy

Penguins replace their feathers in a concentrated annual molt. Unlike birds that replace feathers gradually while remaining able to fly, penguins need a complete waterproof coat for efficient swimming. During the main molt they remain ashore and do not feed at sea, relying on energy stored beforehand.

A molting adult can look swollen, patchy or unkempt as old feathers lift and new ones emerge. That appearance is normally part of the cycle, not automatic evidence of illness. Visitors must not pull loose feathers, offer food or try to move the bird toward water.

Chicks also lose their down as juvenile plumage develops, but this first transition is not identical to the adult’s annual molt. Observe body condition and behavior without diagnosing an individual from one photograph.

 

 

What life-cycle phase might you see by month?

September and October: return, courtship, territory and nest preparation become important, although visitor operations and exact colony timing vary.

November and December: incubation, hatching and small chicks may overlap. Not every nest is synchronized.

January: many chicks are larger and more visible; feeding trips, crèche-like groups and shoreline activity can be prominent.

February and March: fledging, juvenile departures and molt can reshape the colony. Some excursions continue through March, but bird numbers are not fixed.

These are broad biological expectations, not a guarantee for a date. Check the current product availability. The Martillo Island navigation currently lists daily departures from November through March, with observation from the boat.

How to observe nesting birds responsibly

• Stay with the guide and on the designated route.
• Never stand between a penguin and its nest, chick, partner or the sea.
• Give way when a bird crosses; do not create a ring of people around it.
• Keep voices low and movements slow.
• Do not use flash or playback calls.
• Use a telephoto lens and accept natural vegetation around the subject.
• Do not touch feathers, eggs, nest material or burrow entrances.

 

The guided penguin walk on Martillo Island limits the group and follows specialized instructions. A boat-based visit offers a different perspective and no landing. Choose the format that fits your mobility and interests, not the one you imagine will put you closest to a chick.

After more than 25 years in tourism: I encourage travelers to ask “Which phase is happening?” rather than “Will I see a chick?” The first question opens a richer natural-history experience; the second can create a promise nature cannot keep.

Share your travel dates and preferred observation style. We can explain the likely stage of the season, current tour format and the limits that protect the colony.