The macaroni penguin is mainly active during the day. Very little is known about this species outside of the breeding season; most studies have been carried out on breeding birds. The macaroni penguin feeds mainly on krill (shrimp-like crustaceans), although in some areas fish become an increasingly important food source as the breeding season progresses (5). It has been estimated that macaroni penguins alone consume four million tonnes of krill each year (6). In some populations, dives typically take the form of a V-shape, reaching depths of 48 metres (4), although in other populations, the dive profiles are more complex (5).
Macaroni penguins return to the breeding colonies each year in October and November, with males arriving before the females (4). Individuals often have to walk hundreds of metres over screes to reach their nest site (2). Macaroni penguins are monogamous and pair bonds are long-lasting. Each year the pair reunites at the same nest location, recognising each other by means of their calls (4). Pairs often perform a display known as the ‘ecstatic display’, in which their heads are swung from side to side (4). The nest is a simple scrape in the ground, typically lined with small rocks. In some cases, it may be built on a patch of grass and lined with grass shoots (4). Two eggs are laid; the second egg is always larger than the first and is usually the only successful egg per nest. If both eggs are lost, the pair is unable to produce a replacement brood (3).
The incubation of the eggs takes up to 37 days and is shared by the adults in three main shifts. The first shift lasts for 8 to 12 days and is shared by the male and female. The second shift (12 to 14 days) is carried out by the female, and the final shift (9 to 11 days) by the male. During each shift, the non-incubating penguin goes to forage at sea during the day (2) (4). The newly hatched macaroni penguin chicks are helpless, and for the first 23 to 25 days they are guarded and brooded by the male, while the female forages and feeds the chicks each day by regurgitating food (4). After this period, the chicks have developed their first plumage, which allows them to maintain their own temperature and so leave the nest. They cluster into small crèches for protection; at this stage, both adults are able to forage (3). Most chicks will have fledged by 60 to 70 days of age (4), at which point they have developed waterproof plumage (3). The macaroni penguin does not start to breed until five years of age in females and six in males (4).
After the chicks leave the breeding colonies, the adult macaroni penguins feed at sea for around three weeks before the annual moult. During the moult they are unable to forage, as the plumage is not watertight. After the 25 day moult the adults leave the colonies to spend the winter at sea (3).
In undisturbed macaroni penguin colonies, predation is relatively low. Eggs (mainly deserted ones) are predated upon by skuas, sheathbills, and kelp gulls, while weakened chicks, or those separated from the crèche, are taken by skuas and giant petrels. Whilst at sea, adult macaroni penguins are predated upon by leopard seals and Antarctic fur seals (4).