The macaroni penguin (Eudyptes chrysolophus) is a species that breeds in sub-Antarctic regions and surrounding islands, with its diet primarily consisting of krill, small fish and squid. The breeding population, estimated at around 9 million pairs in the mid-20th century, has declined to below 6.3 million pairs by the 2020s due to factors such as fluctuations in krill stocks linked to climate change, industrial fishing pressure, and declines in breeding success. This significant decline led to the species being listed as ‘Vulnerable’ (VU) on the IUCN Red List. Protecting food sources and carefully monitoring changes in marine ecosystems are crucial for the future of the macaroni penguin.

Morphological Characteristics and Systematic Position

Physical Description

The macaroni penguin (Eudyptes chrysolophus) is a penguin that can reach an average length of approximately 70 cm and weigh between 3 and 6 kg, depending on the season and sex; before breeding, males and females sometimes reach weights of 5–5.5 kg. The upper body is glossy black, the belly white; its most distinctive feature is the orange-yellow crest extending from the head to the sides. There is a bare area of pale pink skin around the eyes; this ‘periorbital’ area probably contributes to thermoregulation. The wing bones are densified to provide powerful propulsion for swimming rather than flight, and the feathers are densely packed and covered with a thick layer of oil, providing waterproofing and thermal insulation. There is no obvious visual difference between the sexes in adults; males tend to be slightly larger and have a more robust beak structure.

Taxonomy and Evolution

The macaroni penguin (Eudyptes chrysolophus) is taxonomically classified within the genus Eudyptes and is most closely related genetically to the royal penguin (E. schlegeli); molecular studies suggest that these two lineages diverged from each other approximately 1.5 million years ago. Furthermore, mitochondrial gene analysis clarifies the macaroni penguin's position within the Spheniscidae family, while mitogenomic data from E. chrysolophus has been compared with other penguin species to construct phylogenetic trees. Although fossil records suggest that the diversification of the genus Eudyptes may date back to the Middle-Late Miocene period, analyses based on current genetic data indicate that the macaroni/royal lineage diverged relatively late. Oceanographic boundaries — particularly the Antarctic Polar Front (APF) and the Subtropical Front (STF) — may have acted as barriers restricting genetic flow between these species; some population genetic analyses suggest an indistinct difference between macaroni and royal penguins.

^{Macaroni Penguin (Unsplash)}

Ecology, Behaviour and Life Cycle

Habitat and Distribution

The macaroni penguin (Eudyptes chrysolophus) establishes breeding colonies ranging from South Georgia to Heard Island and sub-Antarctic islands; these colonies are typically located in relatively safe habitats such as rocky slopes, pebbly shores, or creeping seaweed cover. Feeding movements, in line with the penguin's ‘colony-based foraging’ strategy, can extend up to 50–300 km from the colony (maximum ranges have been recorded around Heard Island). The typical diving depth underwater is ~25 m ± a few metres; deeper dives (e.g., up to 100 m) have also been observed. These dives typically last between 1 and 2 minutes and occur at shallower depths at night or in low light conditions. The Macaroni penguin conducts most of its underwater feeding in the 10–60 m range, where krill and other small marine organisms rich in nutrients are abundant; diving intensity is higher during the morning–midday period of the day, while it tends to decrease in the evening hours.

Nutritional Ecology

The diet of the macaroni penguin (Eudyptes chrysolophus) is predominantly based on krill species; studies have reported that during the breeding season, krill constitutes >50% of the food mass, with fish and squid contributing to a lesser extent. This species employs different feeding strategies: it can catch krill species in the lower water column through deep dives, or hunt small fish during shallower dives or ascent. Macaroni penguins generally hunt individually; no collective pressure tactics in the form of ‘dives synchronised with a net pattern’ have been reported. 

Reproductive Biology

The macaroni penguin (Eudyptes chrysolophus) exhibits monogamous behaviour, and pairs usually return to the nest used the previous year. The breeding season coincides with spring and summer in the southern hemisphere; adults typically arrive at the colonies at the end of October and lay their eggs in early November. The female lays two eggs in the same season; the first egg is usually smaller and has a lower chance of survival, so in most cases only the second egg hatches and is raised. The incubation period varies between 33 and 37 days, with both parents taking turns incubating the eggs in long shifts. For the first 3–4 weeks after hatching, the male protects the chick in the nest while the female goes out to sea to forage for food; later, the chicks join groups called ‘nurseries’ where they are protected and the parents take turns bringing them food. The chicks leave the nest and enter the sea after approximately 60–70 days. The period when they acquire their adult plumage coincides with this period, and after this period, the young individuals leave the colony. During the moulting period, all individuals remain on land for two to three weeks and do not feed; it is vital that individuals have sufficient fat reserves during this process.

Conservation Status

The macaroni penguin (Eudyptes chrysolophus) was classified as Vulnerable in the latest 2020 assessment of the IUCN Red List; this classification is based on the sharp population decline observed over the last three generations (approximately 37 years). Despite having a wide distribution range, population declines have been recorded in many breeding colonies. Therefore, although the distribution criterion has not fallen below safe thresholds, the decline signals are noteworthy in terms of the trend criterion. Although the population size is still expressed in terms of millions of breeding pairs, the continuing decline threatens to undermine this size.