The Erect-crested penguin (Eudyptes sclateri) is probably the least researched of all the world’s penguins. Historically recorded on Campbell Island, it now breeds only on the Bounty and Antipodes Islands. Their numbers declined throughout the 20th century, although that decline may have slowed in the last two decades. The reasons for the decline are unknown, but for this species introduced predators and fishery bycatch are not implicated. Erect-crested penguins are related to, larger than and distinct from, the two other crested penguins endemic to New Zealand, Fiordland penguin (E. pachyrhynchus) and Snares penguin (E. robustus). Another now extinct crested penguin, was probably also endemic to the New Zealand region, and based on mitochondrial DNA, was sister to the erect-crested. This taxon (currently referred to as Eudyptes Clade X) was probably hunted to extinction following human arrival.

Erect-crested penguins are assumed to feed well offshore and migrate to parts unknown between breeding seasons. They arrive at the Antipodes and Bounty Islands in September, chicks are fledged in late January, there is a pre-moult exodus of about one month, many moulting at their breeding colonies. Once moult is finished the penguins remain at sea until they return to breed about six months later.

As with other Eudyptes penguins, Erect-crested penguins are sexually dimorphic, with males being heavier and with larger bills than females. Weights and measurements of sexed adults are given by Warham¹ who found yearlings and even fledglings showed dimorphism in bill measurements^1,2.

The chapter by Davis³ presents a good review of what little is known about this enigmatic penguin. Marchant & Higgins⁴ is more encyclopaedic drawing together snippets of information often overlooked in other reviews. The comparative review of the crested penguin species by John Warham² is still a useful overview particularly of those species that breed in the New Zealand Region.

Other descriptions of the Erect-crested penguin^5,6, were written primarily for the lay person and provide brief introductions to the species.

Two recent workshops, one for seabirds in general⁷ the other for New Zealand penguins⁸ identified research required for the conservation of New Zealand penguins. Neither went through peer review and both are less detailed than required for our purposes. Research and conservation priorities for Erect-crested penguins have been listed by Taylor⁹, Davis³ and Baird¹⁰; all are brief, all identify on-going declines being of concern, and serve to emphasise how little is known about the species, its threats or the conservation actions required.

The Department of Conservation lists the Erect-crested penguin as ‘declining’¹¹ and IUCN as ‘endangered’¹², due to its restricted breeding range and recent population declines.

Erect-crested penguins breed on the Bounty Islands (Proclamation, Tunnel, Depot, Ruatara, Penguin, Lion, Spider, Funnel, Molly Cap and North Rock) and Antipodes Islands (Antipodes, Bollons, Archway and Windward Islands^3,9,13–15. A few have bred on Disappointment IslandA few have bred on Disappointment Island in the Auckland group but none has been seen during annual visits since 2015 (P. Sagar pers. comm.). In the 1940s and in 1958 small numbers bred in amongst rockhopper penguins on Campbell Island¹⁶, but perhaps not the several hundred suggested by Davis³. In 1938 and 1939 a pair nested on Otago Peninsula¹⁷ but there are no recent records of them breeding on Campbell Island or the New Zealand mainland. A female Erect-crested penguin bred with a male Snares penguin at The Snares in 2013; an egg was laid but the breeding attempt failed¹⁸.

Figure 1. Erect-crested penguins breeding in conjunction with Salvins albatross on Proclamation Island, Bounty Islands.

Erect-crested penguins are seldom seen at sea, during the breeding season sightings have been made 160 km ESE, and 255 km E of the Bounty Islands and on approach to those islands⁴. They are assumed to be pelagic when not breeding or moulting, but where they go is unknown. Most sightings and beach-stranded birds found along the south-eastern coasts of the South Island have been found between March and July suggesting that at least some of the penguins move north during winter^4,19.

Between breeding seasons, they are regularly seen on The Snares, the other sub-Antarctic Islands and Chatham Islands, less often on south-east coast of the South Island and Stewart Island, as vagrants in Wellington, Wairarapa, Hawke’s Bay and very rarely elsewhere around the North Island^9,19. Dates of observation and the location of vagrant Erect-crested penguin sightings are listed by Marchant & Higgins⁴. Beyond New Zealand, vagrants have been seen at Macquarie Island²⁰ and southern Australia²¹, and very rarely at the Falkland Islands, Marion Island and Heard Island, where they have been observed attempting to breed with the crested penguin species resident on those Islands¹⁸ with one at sea record in the southern Indian Ocean²².

On the Antipodes Islands, Erect-crested penguins breed in mixed colonies along with eastern rockhopper penguins (E. filholi); the two species readily identified from one another during ground counts but not when counted from clifftop observation points or from boats, as is necessary for some colonies.

Figure 2. Erect-crested penguin colony with Bollons Island in background, Antipodes Island, March 2009 (Photo: Mark Fraser, NZ Birds Online)

There are few attempts to estimate population numbers of Erect-crested penguins but substantial differences in methodology limit direct comparisons^3,9. Robertson & van Tets¹³ estimated 115,000 breeding pairs to be present on the Bounty Islands in 1978 using nest densities on one island to extrapolate to the entire Bounty Island land area deemed suitable for breeding. A similar approach was used in 1997, that estimate being just 27,956 pairs, but as the two studies used different estimates of the area suitable for nesting the two counts are not strictly comparable⁹. A total of 2,774 Erect-crested penguin nests were counted on Proclamation Island, Bounty Islands 12-16 November 1997²³.

Equally unreliable, seems to be a population estimate for on the Antipodes Islands also of 115,000 pairs in 1978, with no details presented describing the methodology that was used to derive this “very rough”²⁴ population estimate.

Therefore, estimates provided by Robertson & van Tets¹³ and Taylor²⁴ - and by extension numbers provided in Marchant & Higgins⁴ which are based on these sources - are of unknown reliability and we have chosen to use them with great caution.

What can be said with certainty, based on photographic evidence, is that the Erect-crested penguin population on Antipodes Island declined substantially between 1949 and 1989²⁴. Between 1995 and 1998, numbers declined by a further 26% (Table 1) when comparable census methods were employed in both years³.

A full ground census on the Antipodes Islands in 2011 recorded about 39,700 breeding pairs which appears to be comparable with the 1998 estimates¹⁴. Hiscock²⁵ includes the location of and the counts made at each individual colony in 2011 and for each sector of the Island in 1995, 1998 and 2011. Twenty-four colonies mapped in 1978 had been abandoned by 2011¹⁴.

The most recent partial survey in November 2014 found the breeding population in those colonies resurveyed had declined, on average, by a further 19% since 2011²⁶. In January 2014, a major storm caused extensive landslides on the Antipodes Islands with 44% of the Erect-crested penguin colonies losing area due to landslides or were partially buried by landslide debris²⁶.

About 20 birds nest on Inner Windward Island, Antipodes Islands²⁷.

From the information at hand it is certain that the Erect-crested penguin populations on both Antipodes and Bounty Islands have undergone significant declines in the 20th Century. However, more robust data are required to assess the extent of those declines and current population trajectories.

TBased on the timing of breeding cycles, it has been suggested that Erect-crested penguins breeding on the Bounty and Antipodes Islands may represent separate ‘cryptic’ taxa. However, a brief examination of mitochondrial DNA by Cole et al.²⁸ did not show any genetic structure in samples obtained, refuting the separate taxa hypothesis.

Cole et al.²⁸ used ancient DNA to genetically identify penguin bones collected from natural fossil deposits and archaeological middens throughout New Zealand. For those few Erect-crested penguin bones (probably vagrants) found, comparison of the mitochondrial Control Region (a commonly used ‘population’ proxy for assessing genetic diversity) from the bone samples (n=2), with historical museum skins (n=10) and contemporary blood (n=18). did not indicate any decline in genetic diversity over time, however, as so few bone samples were available, the results should be interpreted with caution. Future assessment of population demographics using genomic information derived from Single Nucleotide Polymorphisms or whole Genomes, techniques currently in development, may provide clues on the extent of decline in numbers and genetic diversity of Erect-crested penguins.

Regular monitoring of Erect-crested penguins – at least of the Antipodes population – is of high priority. The last full Island survey was conducted between 22 October and 6 November 2011¹⁴. They used ground counts in GPS mapped colonies and present methodology appropriate to and repeatable for Antipodes Island. Hiscock²⁵ describes the survey methodology in greater detail and identifies each of the then extant colonies. They arbitrarily recommend their survey be repeated at five yearly intervals, we suggest two consecutive years at random 3 to 6-year intervals. Some colonies were recounted in 2014²⁶ (Table 1).

There is no monitoring of the Bounty Island population.

On the Antipodes Islands Erect-crested penguins breed on rocky coastal slopes and ledges along with rockhopper penguins, the smaller, later arriving rockhoppers tending to use higher and more broken ground than the Erect-crested penguins¹. Erect-crested penguins put little effort into nest building, at best nests consist of a few stones or bits of vegetation, some pairs laying directly onto bare rock^3,29. On the Bounty Islands, the penguins nest around the margins of open spaces and in crevices, often using bones or decomposing animals for nesting material, avoiding the open flatter ground occupied by the more aggressive Salvin’s albatross (Thalassarche salvini) (Robertson & Van Tets¹³, figures 5 & 6, P. Sagar pers. comm).

Figure 3. Erect-crested penguin breeding incubating its egg on the carcass of a Salvins albatross, Proclamation Island, Bounty Islands, October 2019.

There has been no full season study of the breeding cycle of the Erect-crested penguin. The classic paper by John Warham¹ was based on observations made at the Antipodes Islands between 28 January and 12 March 1969. Further observations were made during a short visit in October 1990³⁰ and from September to November 1998²⁹.

At the Antipodes Islands Erect-crested penguins lay three to four weeks earlier than the rockhopper penguins that share the island with them². Erect-crested penguins return to the Antipodes Islands in September, males a week or so before the females, and are ashore for about 23 days before eggs are laid. The first returning bird was seen by shipwrecked mariners on 5 September 1893 who recorded the first egg being laid on 2 October¹. As with other Eudyptes penguins they lay two eggs, the first being much smaller than the second. The larger B eggs were laid between 9 and 16 October 1990, peak B egg laying being 12 October, with the A eggs about 5 days earlier³⁰. Chicks hatch in the second half of November after an incubation period of about 35 days. Peak fledging was about 30 January in 1969, with just a few chicks remaining by 12 February¹. There are no data on breeding success from the Antipodes Islands, and only very limited data on breeding success at the Bounty Islands¹⁵.

The breeding season is said to be two to three weeks later on the Bounty Islands than at the Antipodes¹³, although in 1997 at the Bounty Islands the first eggs were laid on 5 October¹⁵ and the first egg had pipped on 17 November²³.

Both parents share incubation duties, there is no data on the length of incubation spells. As with other crested penguins, chicks are guarded by the male for the first three weeks after hatching, during which time the females return to feed the chick most days^1,2. After about 10 December the chicks are left alone, often forming crèches. When parents return, the chick chases after its parent with 6-10 deliveries of food during a feeding chase¹; food transfer parent to chick taking place up to 10 m from the nest². Peak fledging has been recorded for the Antipodes Islands around 30 January with most chicks having left by 12 February; parents appear to leave for the sea soon after feeding their chick¹ .

Figure 4. Erect-crested penguins feeding its chick, Antipodes Islands, December 2009 (Photo: David Boyle, NZ Birds Online)

Egg-size dimorphism is more extreme than in con-generic species with the second laid (B) egg being 85% heavier than the first laid (A) egg^3,30. Measurements of A and B eggs for Antipodes Island penguins are given by Davis³ and Miskelly & Carey³⁰ and for Bounty Island birds by Amey²³. The mean interval between laying A and B eggs was 5.4 days, the longest between egg interval for any bird³. The Erect-crested penguin is an obligate brood reducer; 80% of A eggs were lost before or on the day the B egg was laid, and the remainder lost within six days of laying the B egg^3,29,30. Little if any attempt was made to incubate the A egg before the B egg was laid. Davis²⁹ suggested that the eggs are so dissimilar in size that it is essentially impossible to incubate both successfully. Penguins laying later tended to produce larger eggs than early laying birds, and early layers tended to lose the A egg sooner than those that laid late. Davis²⁹ suggested that the A egg serves as a primer stimulating the birds into full breeding mode. Why then do other Eudyptes penguins, where egg dimorphism is less extreme, often incubate both A and B eggs, and hatch both chicks, the Fiordland penguin sometimes even fledging two chicks? An alternative hypothesis has been postulated by Crossin et al.³¹. With egg formation in crested penguins often starting while the females are at sea, the extreme egg size dimorphism in Eudyptes penguins could be due to a physiological constraint imposed by a migratory carryover effect and argue against small A‐eggs having a specific, adaptive function.

Figure 5. Erect-crested penguin at nest with eggs showing extreme size dimorphism between fresh second egg and stained first egg, Antipodes Island, October 1990 (Photo: Colin Miskelly, NZ Birds Online).

The cause and function of egg dimorphism in crested penguins has been debated by many researchers over the last 50 years but has yet to be satisfactorily resolved. The debate continues, and the current theories are discussed by Morrison³².

There is no data on pair and site fidelity or age at first breeding for Erect-crested penguins.

Most of those Erect-crested penguins that had bred had departed on their 30-35-day pre-moult sojourn at sea by 4 February 1969¹. By 27 February 1969 about 75% of the breeding birds appeared to be ashore in pre-moult fat and by 11 March half the birds had begun to shed feathers¹. Males tended to arrive before females and many pairs appeared to moult together at their nest site. Most non-breeders had finished their moult by about 6 March. In 1908 shipwrecked sailors recorded the penguins leaving Antipodes Islands having finished moult about 17 April¹.

Figure 6. Moulting Erect-crested penguins, Antipodes Islands, March 2016 (Photo: James Reardon, The Million Dollar Mouse project)

Yearling Erect-crested penguins returned to the Antipodes Islands, presumably most to their natal colonies, in late January to early February, most had finished moult by 21 February 1969, but a few remained ashore in early March¹. They attained adult plumage at the end of this moult.

Warham¹ gives weights of a small sample of sexed Erect-crested penguins at the start and finish of their moult, both sexes lost about 50% of their pre-moult weight during 26-30 days ashore. They left before the tail feathers were fully grown.

Cooper et al.³³ reviewed what was then known about crested penguin diet, but that paper contains no information of the diet of Erect-crested penguins. Feathers have been collected at the Bounty Islands for stable isotope analysis, but results are not yet available (D. Thompson pers. comm.). Information of foods consumed as well as parasites, bacteria and the sex and genotype of the bird can now be obtained by molecular analysis of scats. This is non-invasive and samples can be obtained even during very brief visits. Any study wishing to utilise this method will need to ensure a genetic database (such as GenBank’s BLAST; https://blast.ncbi.nlm.nih.gov/Blast.cgi) of all potential prey items is available to compare sequence data to, as a reduced database will limit the power of the analysis and miss potential food species.

Erect-crested penguins are assumed to be off-shore foragers making long feeding trips³. To date there has been no at-sea tracking of Erect-crested penguins. Dr David Thompson, NIWA, plans to deploy geolocation tags on penguins at the Bounty Islands hopefully in 2019 with retrieval one year later.

Subantarctic skuas (Catharacta antarctica lonnbergi) prey on penguin eggs and chicks. Fur seals (Arctocephalus forsteri) are known to occasionally kill Erect-crested penguins and leopard seals (Hydrurga leptonyx) may kill the occasional one^3,29. Northern giant petrels (Macronectes halli) gathered on the shoreline when penguins fledged; they ate dead chicks but were not seen to kill Erect-crested penguin chicks³⁴.

There has been no research conducted into diseases or mortality factors of Erect-crested penguins³⁵.

The reason/s for the population decline that has occurred, at least since 1978 and probably earlier is unknown. The usual suspects, introduced mammals can be eliminated for Erect-crested penguins; mice (Mus musculus) which were unlikely to pose a threat to penguins, were the only species of introduced mammal on the Antipodes Islands and were eradicated there in 2016. The Bounty Islands have always been free of introduced mammals. Erect-crested penguins are considered to be at low risk from fishery bycatch³⁶. There is only one record of an Erect-crested penguin accidentally caught during fishing operations; a bird foul hooked in the flipper by a ling (Molva spp.) longliner; it was released alive³⁶. Given the remoteness of both island groups pollution and human disturbance appear unlikely^3,9. Both island groups are uninhabited with only occasional visits from small parties of scientists or conservation workers.

Changes in the marine environment associated with climate change are more likely to have caused population declines. Fluctuations in the populations of rockhopper penguins at Campbell Island are correlated with changes in sea temperature^37,38 and it seems likely that Erect-crested penguins on the Antipodes and Bounty Islands could be similarly affected. Stable isotope ratios from Antipodes Island rockhopper penguins showed a decreasing trend in δ13C since specimens were first collected in 1861, indicating that rockhopper penguin declines may be related to a decrease in either ocean productivity or prey availability³⁹. This is likely to have also affected Erect-crested penguins though evidence to support this is circumstantial.

In January 2014 a major storm caused extensive landslides on the Antipodes Islands, with 44% of the erect-crested colonies losing area due to landslides or were partially buried by landslide debris, with an average 19% decline since those same colonies were surveyed in 2011²⁶. The magnitude of the decline was roughly proportional to the area of colony affected, 11.7% decline in colonies not impacted by landslides, 39.9% in colonies that had lost at least 75% of their area to landslides²⁶. With global climate change major storms such as the one in January 2014 are predicted to become more frequent and could further reduce available breeding habitat or kill penguins. The Bounty Islands are essentially bare rock, so landslides are unlikely to impact Erect-crested penguins there.

On the Bounty Islands the growing population of fur seals occupy an ever-increasing area on those islands in the group accessible to seals thus displacing penguins, with the movements of rampaging bull seals further disturbing penguins (P. Sagar pers. comm.).

Given their restricted breeding range a nearby oil spill, perhaps unlikely, could be disastrous.

Feral sheep (Ovis aries), cattle (Bos taurus), Norway rats (Rattus norvegicus) and cats (Felis catus), were present on Campbell Island but all have now been eradicated. There is no known link between these mammals and the apparent local extinction of Erect-crested penguins on Campbell Island.

Given that this is probably the least known and least accessible of all penguin species, research and conservation management recommendations presented here are of necessity somewhat subjective. As an endangered species with a restricted range whose numbers have declined markedly for unknown reasons, evidence-based management is urgent. Some of the research identified below for the Antipodes Islands could be undertaken in conjunction with the annual Antipodean albatross monitoring.

1. Population monitoring

2. Marine Ecology

3. Breeding biology

Thanks to Paul Sagar and Tess Cole for their comments on early drafts of this paper and for allowing us to incorporate their observations on the penguins. Graeme Taylor reviewed the research priorities section of this report. Thanks to Barry Baker, David Thompson and Colin Miskelly for information on their planned or past research on Erect-crested penguins. Colin Miskelly, Jacinda Amey and Caroline Cunninghame kindly provided copies of unpublished reports and Louise Chilvers and Jo Hiscock kindly allowed us to include observations of their paper currently in review. This review was funded by the T-Gear Charitable Trust through the Birds New Zealand Research Fund. We are especially grateful to Peter Gaze who facilitated our work and gave encouragement where it was required.

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