The yellow-eyed penguin (Megadyptes antipodes), known also as hoiho, is a species of penguin endemic to New Zealand. It is the sole extant species in the genus Megadyptes, from Ancient Greek μέγας (mégas), meaning "large", and δύπτης (dúptes), meaning "diver".
Previously thought closely related to the little penguin (Eudyptula minor), molecular research has shown it more closely related to penguins of the genus Eudyptes. Like most penguins, it is mainly piscivorous.
The species breeds along the eastern and south-eastern coastlines of the South Island of New Zealand, as well as Stewart Island, Auckland Islands, and Campbell Islands. Colonies on the Otago Peninsula are a popular tourist venue, where visitors may closely observe penguins from hides, trenches, or tunnels.
On the New Zealand mainland, the species has experienced a significant decline over the past 20 years. On the Otago Peninsula, numbers have dropped by 75% since the mid-1990s and population trends indicate the possibility of regional extinction from the peninsula in the next 20 to 40 years. While the effect of rising ocean temperatures is still being studied, an infectious outbreak in the mid-2000s played a large role in the drop. Human activities at sea (fisheries, pollution) may have an equal if not greater influence on the species' downward trend.
Taxonomy The yellow-eyed penguin was first described by Jacques Bernard Hombron and Honoré Jacquinot in 1841.
The yellow-eyed penguin is the sole species in the genus Megadyptes, though there have been multiple subspecies. It was previously thought closely related to the little penguin, but molecular research has shown it is more closely related to penguins of the genus Eudyptes. Mitochondrial and nuclear DNA evidence suggests it split from the ancestors of Eudyptes around 15 million years ago. In 2019 the 1.25Gb genome of the species was published as part of the Penguin Genome Consortium, aiming to understand the origins and aid conservation by helping to inform any future breeding programmes.
Subspecies Megadyptes antipodes antipodes The hoiho or yellow-eyed penguin (M. a. antipodes) is the only extant subspecies. They were formerly most abundant in the subantarctic Auckland and Campbell Islands, and colonised Stewart Island / Rakiura and parts of the South Island following the extinction of the Waitaha penguin.Rawlence, Nicolas J., et al. "Radiocarbon-dating and ancient DNA reveal rapid replacement of extinct prehistoric penguins ". Quaternary Science Reviews 112 (2015): 59–65.
There are proposals to split the yellow-eyed penguin into three further subspecies due to genetic differences. Genome sequencing of 249 penguins from across the New Zealand mainland and the subantarctic Enderby and Campbell Islands identified clear genetic divisions in each location with negligible gene flow between the populations, consistent with there being three distinct subspecies. Based on comparisons of these genomes the authors estimated that the three lineages diverged between 5,000 and 16,000 years ago, although the proposed historic co-existence of two Megadyptes subspecies in southern New Zealand remains unexplained.
Megadyptes antipodes waitaha The Waitaha penguin (M. a. waitaha) is an extinct subspecies that was present in the North Island, the South Island, Stewart Island, and Codfish Island / Whenua Hou. Last dated to AD 1347–1529. It was discovered by University of Otago and University of Adelaide scientists comparing the foot bones of 500-year-old, 100-year-old and modern specimens of penguins. According to lead researcher Sanne Boessenkool, Waitaha penguins "were around 10% smaller than the yellow-eyed penguin. The two species are very closely related, but we can't say if they had a yellow crown". The penguin was named after the Māori iwi (tribe) Waitaha, whose tribal lands included the areas the Waitaha penguin are thought to have inhabited. "Our findings demonstrate that yellow-eyed penguins on mainland New Zealand are not a declining remnant of a previous abundant population, but came from the subantarctic relatively recently and replaced the extinct Waitaha penguin", said team member Dr Jeremy Austin, deputy director of the Australasian Centre for Ancient DNA. Archaeological remains indicate that early Polynesian settlers hunted the subspecies and that this, with possible additional predation by Polynesian rats and dogs, was a probable cause of extinction. As the local Māori people have no record of this subspecies, it is estimated to have perished between c. 1300 and 1500, soon after Polynesian settlers arrived in New Zealand. It was first described as a new species M. waitaha in 2009, but reclassified as a subspecies M. a. waitaha in studies from 2019 and 2022. After their extinction, their range was occupied by yellow-eyed penguins (now M. a. antipodes), previously most abundant further south in the subantarctic islands. The decrease in sea lion populations after human settlement may also have eased their expansion. Another coauthor, Dr Phil Seddon, said "these unexpected results highlight ... the dynamic nature of ecosystem change, where the loss of one species may open up opportunities for the expansion of another".
Megadyptes antipodes richdalei Richdale's penguin (M. a. richdalei) is an extinct island dwarf subspecies from the Chatham Islands. Last dated after the 13th century, it was hunted to extinction.
Description
The yellow-eyed penguin (M. a. antipodes) is most easily identified by the band of pale yellow feathers surrounding its eyes and encircling the back of its head. Its forehead, crown and the sides of its face are slate grey flecked with golden yellow. Its eye is yellow. The foreneck and sides of the head are light brown. The back and tail are slate blue-black. Its chest, stomach, thighs and the underside of its flippers are white in colour. Juvenile birds have a greyer head with no yellow band around their eyes.
It is the largest living penguin to breed on the mainland of New Zealand and the fourth or fifth heaviest living penguin by body mass. It stands tall and weighs .Marion, Remi (1999). Penguins: A Worldwide Guide. Sterling Publishing Co. Weight varies throughout the year, with penguins being heaviest just before moulting, during which they may lose 3–4 kilograms in weight. Males at around on average are somewhat heavier than females at an average of .
The yellow-eyed penguin may be long lived, with some individuals reaching 20 years of age. Males are generally longer lived than females, leading to a sex ratio of 2:1 around the age of 10–12 years.
The yellow-eyed penguin is mostly silent. It makes a shrill bray-like call at nest and breeding sites.
Distribution and habitat
Until recently, it was assumed that M. a. antipodes was widespread and abundant before the arrival of Polynesian settlers in New Zealand. However, genetic analysis has since revealed that its range only expanded to include mainland New Zealand in the past 200 years. Yellow-eyed penguins expanded out of the subantarctic to replace New Zealand's endemic Waitaha penguin (M. a. waitaha). The Waitaha penguin became extinct between about 1300 and 1500, soon after Polynesian settlers arrived in New Zealand. Jeremy Austin, a member of the team that discovered the Waitaha penguin, said, "Our findings demonstrate that yellow-eyed penguins on mainland New Zealand are not a declining remnant of a previous abundant population, but came from the subantarctic relatively recently and replaced the extinct Waitaha penguin".
An island dwarf subspecies from the Chatham Islands, M. a. richdalei, is extinct. The modern population of yellow-eyed penguins does not breed on the Chatham Islands.
Today, yellow-eyed penguins are found in two distinct populations. The northern population extends along the southeast coast of the South Island of New Zealand, down to Stewart Island / Rakiura and Codfish Island / Whenua Hou. It includes four main breeding areas in Banks Peninsula, North Otago, Otago Peninsula and the Catlins. It is also referred to as the mainland population. The southern population includes the subantarctic Auckland Islands and Campbell Island / Motu Ihupuku. There is little gene flow between the northern and southern populations as the large stretch of ocean between the South Island and subantarctic region and the subtropical convergence act as a natural barrier. Based on monitoring between 2012-2017, there are on average 577 breeding pairs per year on Enderby Island in the Auckland Islands, which comprise 37-49% of the total breeding population for the species.
Behaviour
Breeding
The nesting behaviour of yellow-eyed penguins is thought to be the least colonial of all penguin species. While other penguin species nest in large aggregations, yellow-eyed penguins tend to nest in solitary pairs or loose aggregations.
Yellow-eyed penguins begin forming pairs and breeding at around two years of age. An analysis of data collected from 1991 to 2002 showed that the species has a 63% rate of retaining mates each breeding season. The majority of changes were due to the death of their partner.
While they can be seen coming ashore in groups of four to six or more individuals, they then disperse along tracks to individual nest sites up to one kilometre inland. Accordingly, the consensus among New Zealand penguin workers is to use habitat rather than colony to refer to areas where yellow-eyed penguins nest.
The species prefers to nest in forest or scrub habitat with dense vegetation cover. Adults will incorporate vegetation such as twigs, grasses and leaves into their nests, and often return to the same nesting area each year. Breeding sites are frequented year-round, and adults may continue to defend their nest areas outside of the breeding season. Nests tend to be visually isolated from one another, though they are usually in audible distance from each other.
Nest site selection takes place from June onwards, with breeding beginning in late August, followed by incubation from September to November.
After hatching, chicks are guarded by an adult full-time for the first 40–50 days. Incubation duties are shared by both parents, who may spend several days on the nest at a time. For the first six weeks after hatching, the chicks are guarded during the day by one parent while the other is at sea feeding. The foraging adult returns at least daily to feed the chicks and relieve the partner. After the chicks are six weeks of age, both parents go to sea to supply food to their rapidly growing offspring. Chicks usually fledge in mid-February and are totally independent from then on. Chick fledge weights are generally between 5 and 6 kg.
Feeding
Around 90% of the yellow-eyed penguin's diet is made up of fish, chiefly demersal species that live near the seafloor, including silversides (Argentina elongata), blue cod (Parapercis colias), red cod (Pseudophycis bachus), and opalfish (Hemerocoetes monopterygius).Moore, P.J.; Wakelin, M.D. 1997: Diet of the yellow-eyed penguin Megadyptes antipodes, South Island, New Zealand, 1991–1993. Marine Ornithology 25:17–29 Other species taken are New Zealand blueback sprat (Sprattus antipodum) and cephalopods such as arrow squid (Nototodarus sloanii). They also eat some crustaceans, including krill (Nyctiphanes australis). Recently, jellyfish were found to be targeted by the penguins. While initially thought that the birds would prey on jellyfish itself, deployments of camera loggers revealed that the penguins were going after juvenile fish and fish larvae associated with jellyfish.