|Kerry-Jayne Wilson & Thomas Mattern||Document date: 12 April 2019; DOI: 10.36617/SoP.eastrock.2019-04|
The rockhopper penguins are the smallest of the crested penguins and although outnumbered by Erect-crested penguins (Eudyptes sclateri) within New Zealand, are nevertheless globally the most widespread and most numerous of the New Zealand breeding Eudyptes penguins. Rockhopper penguins have a circumpolar range, breeding on many islands in the sub-Antarctic Zone. Currently three taxa are recognised with just one of these, the eastern rockhopper penguin (Eudyptes filholi) breeding in the New Zealand Region; on Campbell, Antipodes and Auckland Islands as well as nearby Macquarie Island. In the early to mid-20th century Campbell Island was the stronghold for the eastern rockhopper penguin, but numbers there have declined by about 94% since the 1940s. Eastern rockhopper populations have also declined in numbers at both Antipodes and Auckland Islands, although the extent of decline is not adequately quantified for those islands. Rockhopper penguin populations have also declined at most other breeding islands elsewhere in the Southern Ocean. A reduction in food availability due to ocean warming associated with climate change is implicated in the declines on Campbell Island and presumably elsewhere, although at some colonies on Campbell Island other threats including predation and harassment by New Zealand sea lions (Phocarctos hookeri) have contributed to the declines observed. The breeding biology, foods and marine ecology of rockhopper penguins has been studied to varying extents at Campbell Island, but there is little information on these birds from the Antipodes Islands. For the Auckland Islands even the distribution of colonies is inadequately mapped and estimations of their numbers there are rough at best.
The chapter by Pütz et al.4 presents a good review of what is known about the southern rockhopper penguin, presenting information on both eastern and western taxa. Marchant & Higgins1 is more encyclopaedic drawing together snippets of information often overlooked in other reviews but as they treat all three rockhopper taxa as a single species, information presented there needs to be used with care. The comparative review of the crested penguin species by John Warham10 is still a useful detailed overview particularly of those populations breeding in the New Zealand Region. Other descriptions of the rockhopper penguin11,12 were written primarily for a general audience and provide rather brief introductions to the species.
Two recent workshops, one for seabirds in general13 the other for New Zealand penguins14 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 Rockhopper Penguins have been listed by Birdlife International15, Graeme Taylor16 and with less detail by Pütz et al.4 and Karen Baird17.
Our review and the research and conservation priorities listed herein relate specifically to the New Zealand populations of the eastern rockhopper penguin.
The Department of Conservation lists the eastern rockhopper penguin as ‘nationally vulnerable’18 and IUCN as ‘vulnerable’2.
All rockhopper penguins were once considered to be a single species (E. chrysocome)1. Birdlife International2 and the Global Penguin Society recognise two species, the northern rockhopper penguin (E. moseleyi)3 and the southern rockhopper penguin (E. chrysocome), the latter with two sub-species4,5. Although many recent papers treat the resident eastern rockhoppers as a subspecies (E. chrysocome filholi)6 the New Zealand checklist elevates these to full species status, the resident eastern rockhoppers as E. filholi and the western rockhoppers as E. chrysocome7. Both northern and western rockhopper penguins have been recorded in New Zealand as very rare vagrants. In this report we follow Gill et al.7 and Banks et al.8 in treating the eastern rockhopper penguin as a full species. A guide to distinguishing between the three rockhopper taxa is given by Heather & Robertson9.
The northern rockhopper penguin breeds only on the Tristan da Cunha Islands and Gough Island in the South Atlantic Ocean and Ile Amsterdam and St Paul Islands in the Indian Ocean3. The western rockhopper penguin breeds in southern South America and the Falkland Islands and the more widespread eastern rockhopper on sub-Antarctic Islands in the Indian and Pacific Oceans4. In the wider New Zealand Region, they breed on the Campbell, Auckland, Antipodes and Macquarie Island4.
All rockhopper taxa have declined in numbers with the global populations of the southern taxon (including both eastern and western rockhoppers) by 34% and northern rockhopper penguins by 57% in the last 37 years2.
Within the New Zealand Region eastern rockhopper penguins breed on Campbell, Auckland and Antipodes Islands and on nearby Macquarie Island1,4. The distribution of rockhopper penguin colonies on Campbell Island has been mapped three times, the early 1940’s, in 198419,20 and 20126. Morrison et al.6 includes a table showing the history of occupation of each Campbell Island colony in 1958, 1975, 1984, 1985-87 and 2010-12. Most colonies are either on the western most peninsula or on the exposed west coast of the Island.
On the Antipodes Islands rockhopper penguins breed in amongst the much more numerous erect-crested penguins. The maps of crested penguin colonies in Hiscock and Chilvers21 and Hiscock22 show 103 colonies fairly evenly distributed around the main island and on Bollons, Archway and the eastern most of the Windward Islands. There is an implied assumption that eastern rockhopper penguins are present in most if not all of these colonies.
The distribution on the Auckland Islands is poorly documented. Known colonies have been mapped by Bell23 and by Cooper24, but both surveys were primarily boat-based with observations made as the vessel cruised slowly along the cliff-bound north, west and south coasts where most rockhopper penguins breed. As most colonies are small and surveying these rugged, cliff-bound, exposed coasts is challenging, it would be easy to miss entire colonies. The 14 known breeding colonies are mostly on the southern half of the west coast and the western sector of the north coast of the main Auckland Island, with just one colony on the south coast of Adams Island, one on Disappointment Island, and four colonies between Chambres Inlet and Falla Peninsula on the east coast23,24.
Rockhopper penguins occur as vagrants or beach-cast individuals on the New Zealand mainland and at The Snares1,25 but few sightings are identified to species level and as all three rockhopper taxa have been positively identified in the New Zealand Region9 these records do not provide reliable insights into the non-breeding distributions of eastern rockhopper penguins. Cole et al.26 genetically identified >40 prehistoric or archaeological midden crested penguin bones collected from North and South Islands, none were from rockhopper penguins. Given the abundance of eastern rockhopper penguins on the New Zealand sub-Antarctic Islands and Macquarie Island, the paucity of records from the New Zealand mainland may be indicative of a more southerly non-breeding foraging range than for the other New Zealand crested penguins.
Campbell Island, once the stronghold of the eastern rockhopper penguin, indeed one of the largest populations of any of the rockhopper taxa, has suffered massive declines since the first population estimate was made by J.H. Sorensen who was a coast watcher there during the Second World War. Since then his initial estimate of five million birds has been reassessed, considering counts, observations, nesting densities and photographs (mostly unpublished) made by more recent observers. Sorensen’s estimate was initially revised downward to about 1.6 million breeding rockhopper penguins (814,550 pairs)19,20, then Morrison et al.6 again adjusted the estimate using knowledge not available to the earlier researchers, suggesting there were 619,925 breeding pairs on Campbell Island in the early 1940’s. Based on colony photos taken in 1942 and re-photographed in 1987, Cunningham and Moors20 estimated that by 1984-87 numbers had declined by 94% to about 103,100 individuals which would translate to a maximum of 51,550 pairs. The 1984 estimate further adjusted to 42,528 pairs6 (Table 1). Cunningham and Moors20 calculated the area occupied by penguin colonies in the 1940’s was 406,600 m2 but just 25,500 m2 in the 1980s. They thought that the decline had begun by 1945 (with a major reduction in numbers until 1956) and attributed the decline to warming ocean temperatures, with a temporary increase in penguin numbers in the 1960’s during a cooling period20,27.
The Campbell population was assessed again in 2012 using a combination of ground counts and photographs, this time estimating the population to be 33,239 breeding pairs, a decline of 21.8% from an adjusted population of 42,528 pairs in 1984 and a 94.6% decline from an adjusted estimate of 619,925 breeding pairs in 19426 (Table 1). The recent declines were greatest between 1984 and 1996 after which time the overall population increased concurrent with lower sea surface temperatures (SST)6. They calculated the decline between 1984 and 2012 to be slower (k = 0.991) than that between 1942 and 1984 (k = 0.940). The population trends were not identical across all colonies, the differences linked to predation by New Zealand sea lions (Phocarctos hookeri) at those colonies most accessible to the sea lions27.
In November 1950 R.A. Falla28 suggested that rockhopper penguins outnumbered erect-crested penguins on the Antipodes Island, the reverse to that recorded by all later surveys. In 1978 a total of 50,000 pairs spread between 86 colonies were estimated to breed on the Antipodes Islands1. No information for the basis for this estimate is given. A survey in 1995 found a maximum of 3,400 pairs on Antipodes and Bollons Islands16 with a total of 4,000 when the Archway Islands were also included29. Photos of the Ringdove Bay colony showed a huge decline from tens of thousands in 1950 to just a few individuals in 199516.
A further estimate of rockhopper numbers was made for the Antipodes Island in 2011; of the 39,701 penguins counted in ground counts, 2475 (7%) were rockhoppers, the rest being erect-crested penguins21. In total 42,689 nests were counted, the remainder from observation points or from a boat, suggesting there were about 2,988 pairs of rockhopper penguins (7% of 42,689) on the Antipodes in 2011 (Table 1).
|Year of count||Campbell Island||Antipodes Islands||Auckland Islands||Reference|
|1942||619,925**||Morrison et al.6|
|1978||50,000*||R.H. Taylor in Marchant & Higgins1|
|1984-87||42,528**||Morrison et al.6|
|1995||4,000||Tennyson et al.29|
|2011||2,988||Hiscock & Chilvers21|
|2012||33,239||Morrison et al.6|
|* estimate of questionable accuracy.
**adjusted population estimates, the original estimates are included in the text above.
A partial survey of penguin colonies at the Antipodes Island in 2014 found that the breeding population in those colonies resurveyed had declined on average by 19% since 201130. In January 2014, a major storm caused extensive landslides on the Antipodes Islands with 44% of the penguin colonies losing area due to landslides or were partially buried by landslide debris30. The magnitude of the decline was roughly proportional to the area of colony affected, with an 11.7% decline in colonies not impacted by landslides, but 39.9% in colonies that had lost at least 75% of their area to landslides30. With global climate change major storms such as the one in January 2014 are predicted to become more frequent.
There are no accurate estimates of the numbers of Rockhopper Penguins at the Auckland Islands. Based on a single day, boat-based survey of the west coast of the main island, plus surveys of parts of the east coast from a dingy during the 1972-73 summer, Bell (1975) estimated there to be between 5,000 and 10,000 pairs at the Auckland Islands. The only other estimate is that by Cooper24 based on a two-day visit to the islands in January 1990. They surveyed the northern and western coasts of the main island and the southern coast of Adams Island from a boat and visited the four known colonies on the east coast. They located nine breeding colonies and based on an apparent reduction in area occupied estimated the total population to be 2,700 – 3,600 pairs24. R. Russ was present during both surveys and thought the colonies were much smaller than he remembered from 1972-73.
While undertaking actual counts is logistically challenging, molecular based monitoring using population genetics and genomics may provide an alternative way to estimate population trends, perhaps even allowing effective population sizes to be estimated (T. Cole pers. comm.).
Numbers have also declined at Macquarie Island where in 2007 the estimate of 32,000–43,000 pairs was significantly less than past estimates2.
Cunningham and Moors20 were the first to link population trends in Campbell Island rockhopper penguins to changes in sea surface temperature (SST), but then the best SST data available were weekly measurements taken near the entrance of Perseverance Harbour, not necessarily indicative of SST where the penguins fed. Average SST were already increasing in the 1940’s and the 5-year running means peaked at 9.7oC in 1948-49 and 9.6oC in 1953-54. Temperatures cooled after 1957 to a low of 8.9oC in 1965, then rose to 10.2oC by 197020. The 1946-56 warm period was when they believed penguin populations declined most rapidly. There was a temporary resurgence in penguin numbers in the one colony where the best data is available following that cool period, the population increase lagging behind the temperature decline, the lag equating to the years it takes fledglings produced to recruit into the breeding population20.
Recent advances in satellite technology, the online availability of oceanographic data and computing power has allowed much more robust analyses of the relationship between SST and changes in penguin populations. Morrison et al.6 were able to compare a 100-year time series (1913-2012) of extended reconstructed sea surface temperatures (ERSST) with changes in penguin populations. The ERSST data were based on ship and buoy SST measurements prior to 1985 and since then also included satellite measurements. Monthly ERSST data were downloaded for a rectangular area centred on Campbell Island, encompassing the expected foraging radius of the penguins during chick-rearing6. While they also used a 5-year moving average for ERSST in their analysis, they could do this for winter as well as summer ERSSTs. In addition to the average ERSST, they were able to compare population changes against temperature anomalies6.
Morrison et al.6 showed that on Campbell Island rockhopper penguin numbers declined during warm periods and recovered during cool periods, although the initial decline began before the regional ERSST began to increase. Since 1996 penguin numbers have rebounded a little, coincident to the current global warming hiatus, lower ERSST and increased abundance of a key prey species6. The timing of population fluctuations and changes in ERSST are not exact, one changing a few years before the other, partly due to the lag before fledglings join the breeding population but complicated by other marine factors6. They predict the long-term population decline will begin again once global climate warming resumes.
ERSST for both summer and winter from 1913 to 2012 reveal three periods of contrasting trends: a cool period 1913–1950, a warm middle era 1951–1989 with cooler years in the late 1960s, and a return to cooler temperatures 1990–2012, with a few warmer years in the early 2000s6. The average difference in monthly ERSST values was just 0.30oC between the 1913–1944 era when rockhopper populations were large and the 1945–1995 period of decline, and this was driven more by temperature increases over winter than summer. The increase in penguin numbers between 1996 and 2012 corresponds to a decline of just 0.06°C relative to the preceding warm period, driven primarily by lower temperatures over spring and summer6.
The frequency of seasonal temperature anomalies is probably more significant than the ERSST means. During the 1913-1944 cool period just 3.1 % of years had ERSST temperature anomalies, whereas during the 1945–1995 warm period 17.6 % of years were unusually warm, but none were as warm as those anomalous years in the 1996–2012 cool period6.
The penguins are not responding to SST directly but to changes in food availability within foraging range from their breeding colonies, with better foraging conditions during years with low SST than warmer SST. It appears that rockhoppers experienced greater food availability, consequently higher reproductive success and survival during the cooler period after 1990. The average year class strength of Southern blue whiting (Micromesistius australis), the main prey of the Campbell Island rockhopper penguins was c.3.8 times greater during the recent cool era (1990–2009) than the warmer years of 1977–19896.
Stable isotope ratio analysis (SIA) of carbon and nitrogen can provide information on the trophic level targeted. SIA is based on the predictable and quantifiable ways that the ratio of carbon isotopes 13C and 12C, expressed as δ13C and nitrogen isotopes 15N/14N expressed as δ15N change at different trophic levels (Hilton et al. 2006). Hilton et al.31 compared δ15N and δ13C from the feathers from living penguins with those from museum specimens, some collected during the 19th century, to see how diet may have changed over time.
Hilton et al.31 treated all rockhopper penguins as a single taxon, thus including in their analysis the northern rockhoppers from Tristan du Cuna and Amsterdam Islands, western rockhoppers from the Atlantic and eastern rockhoppers from the Indian, and Pacific Oceans. They include data from rockhopper penguins from Campbell and Antipodes Islands and it is the results from these two sites discussed here. δ13C decreased significantly over time at seven breeding sites, including the Antipodes, but not at Campbell Island where no significant isotopic trends were evident31. The decrease in δ13C values at Antipodes Islands, and those other sites where δ13C declined, is indicative of decreases in primary productivity in the seas exploited by penguins from those sites, correlated with the observed declines in those penguin populations31. There was some evidence of a long-term decline in δ15N at some sites, indicative of a shift in diet to prey of lower trophic status, although this was not significant for Antipodes Island31.
Except for a few open nests, tawaki are cryptic breeders that prefer to nest in inaccessible locations. Along open coast sites like Jackson Head, the penguins tend to breed in dense, impenetrable kiekie shrub often in small clusters of nests2. At Gorge River, the penguins breed in a more open forest setting, primarily under tree roots or fallen trees, in amongst kiekie or tangles of supplejack (Ripogonum scandens)33. In Harrison Cove, Milford Sound less than a third of all nests are under rock overhangs or upturned tree roots. Most of the nests are in rock crevices or in cavities and caves under rock falls. At Sinbad Gully, Milford Sound, the penguins occupy a steep slope that is dominated by windfall of rimu (Dacrydium cupressinum) and other large trees; a few kilometres up the fjord, the majority of the penguins nest in an extensive warren under remnants of a glacial moraine32. On Codfish Island/Whenua Hou, the penguins breed in dense tree fern groves, mainly in dug out, deep burrows in the soft peaty soil or in deep hollows under tree roots, while along the north-east coast of Stewart Island the penguins breed in sea caves and fissures in cliffs only accessible from the sea (Mattern, pers. obs.).
Nests usually consist of shallow bowls lined with twigs and stones (Fig. 1).
Figure 1. Eastern Rockhopper nest, Penguin Bay, Campbell Island, November 2010 (Photo: Kyle Morrison, NZ Bird Online)
Rockhopper penguins breed in colonies that range in size from a few tens to thousands, in some colonies nest density may exceed two nests per square metre. On the Antipodes Islands, rockhopper penguins nest in mixed colonies alongside erect-crested penguins, the rockhoppers often with some form of overhead shelter, tending to be above, inland from and in rougher terrain than the larger erect-crested penguins10,28. Rockhoppers may nest in small caves, under boulders and among tussocks up to 200 m inland and up to 100 m above sea level11.
As with other crested penguins rockhoppers lay a single clutch of two eggs each year. The smaller first laid A egg followed 4-5 days later by the larger B egg4,32. The breeding biology has been studied intensively at Macquarie Island33 and references cited therein). Incubation begins once the B egg is laid and normally the A egg, or the chick from the A egg is lost during incubation or soon after hatching. Proportionality more rockhopper penguin A eggs hatch than in most other crested penguins, but only under exceptional circumstances do both chicks fledge. The incubation period is 32-34 days with the female taking the first incubation spell while the male is at sea, his opportunity to replenish body reserves after a month ashore. At Macquarie Island the male’s foraging trip lasts on average 12 days (range 9-17 days)32, at Campbell Island 13-16 days27 during which time the female must remain ashore incubating the eggs. After hatching the male remains at the nest guarding his chick for about three weeks, during which time the female alone provisions the chick, usually returning with food daily. On first leaving his chick the male usually makes a multi-day foraging trip, typically of 7-11 days, replenishing his own body reserves after a fast of over three weeks when he was confined to the nest4,34.
The cause and function of egg-size 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 Morrison35.
Once the guard stage is over, chicks form creches while waiting for their parents to return with food. Once the male ends his post guard foraging trip, both parents return to feed their chick at or close to the nest every few days, until the chick fledges about 70 days after hatching4,34. Well-fed rockhopper penguin chicks can reach a peak weight greater than that of their parents, slimming down before fledging10. As with other crested penguins there is delayed maturity and few breed before they are five years of age, but contrary to Warham’s10 assertion that they breed annually thereafter, more recent research at Macquarie Island showed just 8% of males and 3% of females bred in all three study years33. Their breeding biology is similar at Campbell Island27.
At Macquarie Island the first males arrived at their breeding colonies between 14 and 17 October in 1960, 1961, 1993, 1994 and 199532,33, with the timing of the breeding cycle constant between years33. The females joined their mates at the nest on average 6.5 days later. Laying was well synchronised as in other crested penguins10. At Macquarie Island eggs were laid between 7 and 18 November32; the median date of laying the A egg was 13 or 14 November (1993-1995) and the B egg 17-19 November33. The interval between arrival and laying of the second egg was 17 to 21 days32.
At Macquarie Island the median hatching date was 18-21 December (1993-1995)33 with both parents present at the time of hatching. At Antipodes Island the guard stage lasted until at least 27 December 2002, the median end of the guard stage being 30 December36. During the guard stage females usually returned from mid-afternoon each day to feed chicks, while during post-guard stage males returned most evenings with female parents returning less often; the chicks being fed most days in both guard and post-guard stages6. At Macquarie Island chicks fledged between 24 February and 10 March32, the median date over three years ranging from 21 to 24 February33. The timing of the breeding season is similar at Campbell island34,35,37 with the dates for each stage of the cycle in Table 1 of Morrison et al.37.
At the Antipodes Islands rockhopper penguins breed about 12 days earlier than at Macquarie Island, probably arriving about 7 October, a month after the erect-crested penguins with whom they share colonies. Antipodes rockhoppers laid about 1 November with eggs hatching about 4 December28,38. By late January chicks were well grown, some were fully feathered by 5 February; the first chicks left the island on 9 February 1969 and most had fledged by 20 February28,38. Breeding at Campbell Island is earlier than Macquarie but later than at Antipodes Island, with the peak of egg-laying about 9 November38. At Campbell Island chicks fledge mid-February27.
Morrison et al.34 compared breeding success and foraging trip durations, the frequency at which chicks were fed and chick growth in rockhopper penguins at Campbell Island in 2011 when food was abundant, with 2012 when food was scarce. In 2012, both hatching success (0.69 in 2011, 0.58 in 2012) and reproductive success (0.60 in 2011, 0.35in 2012) were lower, and mean foraging trips during guard and creche stages longer than in 2011 when feeding conditions were more favourable. Chicks were fed about half as often in 2012 and mean chick mass at 30-31 days of age in 2011 was 1466 +/-201 g compared to 1025 +/- 233 g in 201234.
It has been suggested that the breeding regime of crested penguins, where the male has an unbroken three- to five-week period fasting ashore during late incubation and the guard stage, followed by a multi-day foraging trip before he can begin to provision the chick, limits these penguins ability to respond when food is in short supply34. This they postulate, renders crested penguins more vulnerable to climate change than other penguin species where both sexes alternate brooding and feeding during the guard stage.
At Macquarie Island year to year nest site and mate fidelity has been reported to be about 50%.4, a statement at odds with Hull et al.’s33 finding that few individuals breed in consecutive years. At Campbell Island nest site and mate fidelity was high (Kyle Morrison unpubl. data).
At Macquarie Island a few non-breeding birds were ashore from the start of the breeding season until the end of the guard stage. They had limited success at finding partners until incubation and chick rearing was underway when fewer aggressive breeding penguins were present, and non-breeders had greater freedom to wander through the colony seeking partners32. Some non-breeding birds managed to acquire nest sites vacated by failed breeders and form partnerships32.
At Campbell Island first year non-breeding penguins began coming ashore in early December and were common from mid-December through January. The last count was made just before observers left the islands in late January in both 2011 and 2012 was the highest suggesting numbers ashore may have continued to increase later in the summer34. At Macquarie Island yearlings were first seen ashore about 10 December, they were quieter than and dominated by older penguins, some formed short-lived liaisons with other immatures, non-breeding adults or even chicks.
At Campbell Island sub-adults moult in January27 while at Antipodes Island most yearlings had moulted by about 15 February and all adults appeared to be at sea on their pre-moult excursion on 12 March28. On Macquarie Island the pre-moult absence lasts 28-35 days suggesting that adults would return to the Antipodes to moult about 5-10 April28. At Macquarie Island yearlings began moult around 16 January, non-breeding adults in late February and breeding birds from late March32.
Figure 2. Eastern Rockhopper penguins moulting on Campbell Island, january 2012 (Photo: Kyle Morrison, NZ Birds Online)
Rockhopper Penguins are opportunistic foragers, with variation in their diet and foraging ecology between the different breeding populations, presumably reflecting availability more so than preference4.
The most common prey taken by eastern rockhopper penguins at Campbell Island in 1985 and 1986 were dwarf cod (Austrophycis marginata), and juveniles of southern blue whiting and hake (Merluccius australis), in contrast to a euphausiid dominated diet elsewhere20,36,39. At Macquarie Island, euphausiids principally Euphausia vallentini comprised 62% and 70% of food by weight in two different studies40–42 in which the euphausiid Thysanoessa gregaria40 and the fish Krefftichthys anderssoni42 were other important prey. At Macquarie Island one Zanclorhynchus spinifer was 60 mm long and five Nothothenia sp were <100 mm in length40.
Cooper et al.39 reviewed what was then known about crested penguin diet and compare the foods of southern rockhopper penguins across their range. The prey species taken by Campbell Island rockhopper penguins are listed in Table 2. Xavier et al.43 recorded eight species of juvenile and sub-adult cephalopods taken by rockhopper penguins at Campbell Island, with Onykia ingens, Martialia hyadesi and Octopus campbelli being the most important species by frequency of occurrence, number and mass. There is little other information on the diet of rockhopper penguins from the New Zealand Region.
|Giant warty quid
|Greater hooked squid
|Sevenstar flying squid
|Southern blue whiting
The mean fledgling weights of Campbell Island chicks in 1987 and 1988 was 1,992g (1,560-2,400g), significantly lighter than western rockhopper penguins at the Falkland Islands, the difference attributed to their fish diet20.
A fish-based, high tropic level diet is often assumed to be better for penguins than a diet based on lower trophic level cephalopod and crustacean prey. However, contrary to predictions a study using stable isotopes found that during incubation male Campbell Island rockhopper penguins were heavier in 2011 when lower trophic level, offshore, pelagic, zoo-plankton dominated their diet than in 2012 when their diet was primarily benthic, inshore, fish and cephalopods37. Similarly, in 2011 average chick mass was higher than in 2012. They attributed this unexpected result to the low energy density of the southern blue whiting that was thought to dominate their diet in 201237.
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.
Within the New Zealand Region there has been just one study tracking rockhopper penguins at sea. This was conducted on the Antipodes Island from 18 December 2002 to 3 January 200336. During the guard stage eight tracked females foraged 22-54 km (mean 36.4 km) from their colony. The mean distance travelled on a feeding trip was 81.6 km (range 50-114 km), going NNE to feed where the sea was 500-1,500 m deep, or east to waters >1,500 m in depth36. During the guard stage the mean duration of feeding trips for tracked birds was 1.37 days, significantly longer than that of birds unimpeded by tracking devices. Two female penguins were tracked on post-guard trips, for one the trip duration was 5.67 days, the maximum distance from the colony 104 km, in total traveling an estimated 243 km. The other was at sea for 6.92 days, at furthest was 119 km from the colony and travelled about 325 km36. Both foraged along the subantarctic slope in waters >1,500 m deep.
Rockhopper Penguins spend the five to six months between breeding seasons at sea, seldom if ever touching land. Campbell Island adult Rockhopper penguins spent the winter south-east or east of the island some birds travelling about 15,000 km during that period44. On average the maximum distance from the Island was about 2,000 km, with one bird 4,000 km from the island.
Of the three islands in the New Zealand Region where rockhopper penguins breed, Antipodes Island had only mice (Mus musculus, eradicated in 2016). At Campbell Island sheep (Ovis aries), cattle (Bos taurus), Norway rats (Rattus norvegicus) and cats (Felis catus), all since eradicated were present. At the Auckland Islands feral cats, pigs (Sus scrofa) and mice are present on the main island but there are no introduced mammals on Disappointment and Adams Islands, the only other islands in the Auckland archipelago where rockhopper penguins breed. On Campbell Island disturbance by sheep or people did not contribute to population declines as population trends were similar in colonies accessible and inaccessible to these mammals19,20. Rats did eat penguin eggs and small chicks, but only cracked or broken eggs could be taken by rats and it was not determined if the chicks eaten were preyed upon or scavenged by the rats19,20. There was no evidence to suggest cats preyed on the penguins. Today, within the New Zealand Region, introduced predators co-occur with breeding rockhopper penguins only on the main Auckland Island, but as most penguin colonies are at the base of cliffs, introduced predators appear to have little if any impact.
Genetic means can now be used to detect prey items in the scats of predatory mammals (http://www.ecogene.co.nz). This method may provide clues as to the scale of impact invasive mammals have on the Auckland Island rockhopper penguin populations.
Native predators do however kill rockhopper penguin eggs, chicks and adults. Subantarctic skuas (Catharacta antarctica lonnbergi) are present on all islands where these penguins breed and they take both eggs and chicks. Skuas were the main cause of egg and chick loss at Campbell Island in 2011 and 2012 when skua predation was studied at the Penguin Bay rockhopper colonies27. In the smallest of the four colonies (mean: 26 pairs/year) 44% of eggs were taken by skuas, compared with just 7% in the largest of the colonies (mean: 1,476 pairs/year) where there were proportionality fewer peripheral nests. Many of the A eggs were scavenged rather than predated and whether they were taken by skuas, they would not have resulted in a fledged chick. Proportionality fewer B eggs were taken by skuas in larger than the smaller colonies27. Skuas were better able to steal eggs when the smaller females were incubating than the larger more aggressive male penguins27.
At the Antipodes Islands northern giant petrels (Macronectes halli) gathered on the shoreline when penguins fledged, they ate dead chicks but were not seen to actually kill penguin chicks28. On Campbell Island northern giant petrels were observed or implicated in killing a small number (<10 per breeding season) of sub-adult and adult rockhopper penguins27.
At Macquarie Island rockhopper penguins were seen bearing injuries from attacks by New Zealand fur seals (Arctocephalus forsteri)32. Fur seals were seen preying on rockhopper penguins at Campbell Island in the 1940’s45 but not between 2010 and 2012; conversely New Zealand sea lions regularly preyed on sub-adult and adult penguins in the latter but not in the former period6,27. Sea lions were uncommon at Campbell Island in the 1940’s (<20 pups born/year) but more common in the 21st century (&rt;681 pups born in 2009)6. The sea lions could only access some of the Campbell Island rockhopper penguin colonies but at those colonies they can contribute to a decline in penguin numbers. At the Penguin Bay colonies sea lions were estimated to kill 6% of the adult penguins present in 2011 and 3.6% in 201227, and their calculations of adult survival suggest that sea lions accounted for most if not all the adult mortality during chick rearing. Most of the sea lion predation was probably by just one or two male sea lions, although at least six individuals were seen to kill penguins. Predation occurred only in the water or during chases where the penguin managed to jump ashore and was then caught by the pursuing sea lion. Sea lions also contributed to egg, chick and adult deaths by trampling when the mammals blundered their way through penguin colonies27. While sea lions are contributing to the ongoing decline of the Penguin Bay colonies, these colonies represent just 9% of the Campbell Island rockhopper penguin population. Thus, control of the sea lions is not recommended27.
Antipodes Islands: Not a threat
Campbell Island: Not a threat
Auckland Islands: minor
The reason(s) for the population decline that has occurred since the 1940’s at Campbell Island and since at least 1978 at the Antipodes Islands were probably due to marine based threats. Ashore, introduced mammals are unlikely to have had a significant role in declines of rockhopper penguins. Norway rats, feral cats, feral sheep and feral cattle were present on Campbell Island but all have now been eradicated. There is no known link between these mammals and the declines in penguin numbers, although prior to their eradication rats may have helped spread avian diseases. The house mouse was the only species of introduced mammal on the Antipodes Islands (eradicated in 2016). There is no information on the impact introduced pigs, cats and mice have on rockhopper penguins on the main Auckland Island but, as most penguin colonies are at the base of cliffs, the penguins are probably protected from depredations by these mammals. Pigs may restrict those main island locations where penguins can breed.
Antipodes Islands: Not a threat
Campbell Island: Not a threat
Auckland Islands: Not a threat
Sub-Antarctic skuas take penguin eggs and chicks, and giant petrels, fur seals and sea lions occasionally prey on fledglings and even adult penguins. Predation by sea lions is an issue at some Campbell Island colonies. Predation by these native predators does not appear to have population level effects on penguin numbers but have contributed to localised declines at some colonies accessible to sea lions. Predation by skuas at colonies already in decline for other reasons can accentuate the fragmentation of colonies and by creating a greater proportion of edge nesters result in increased losses of eggs or chicks27.
Antipodes Islands: Medium
Campbell Island: Minor
Auckland Islands: Minor
The major storm in 2014 clearly impacted Antipodes Islands penguin populations30. With global warming storms are predicted to become more frequent and more intense and could further reduce breeding habitat or kill penguins. Storm impact is perhaps more likely on the Antipodes Islands; the Campbell and Auckland Island colonies are perhaps in locations where landslides are less likely.
Antipodes Islands: Not a threat
Campbell Island: Not a threat
Auckland Islands: Not a threat
Given the remoteness of these islands pollution and human disturbance appear unlikely16. The islands are uninhabited with only occasional visits from small parties of scientists or conservation workers. A few ship-based ecotourist groups visit the Islands each year. At Campbell and Auckland Islands sites where tourist landings are permitted are well away from rockhopper penguin colonies. No tourist landings are allowed at the Antipodes Islands. The flipper bands previously used on crested penguins increase drag when the birds are swimming, they can cause excessive feather wear and can spring slightly open and catch on vegetation or other obstructions16. These bands are no longer used on crested penguins.
Antipodes Islands: Major
Campbell Island: Major
Auckland Islands: Major
Changes in the marine environment associated with global climate change pose much greater threats to rockhopper penguins than any land-based threats. Fluctuations in the populations of rockhopper penguins at Campbell Island are correlated with changes in sea surface temperatures20,37 and it seems likely that rockhopper penguins on the Antipodes and Auckland 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 availability31.
Antipodes Islands: Unknown
Campbell Island: Unknown
Auckland Islands: Unknown
Rockhopper penguins are considered to be at low risk from fishery bycatch47. Whether competition with fisheries for favoured food species occurs in the New Zealand Region remains unclear.
Antipodes Islands: potentially Major
Campbell Island: potentially Major
Auckland Islands: potentially Major
An oil spill close to islands where rockhopper penguins breed, perhaps unlikely, could be disastrous.
Antipodes Islands: Unknown
Campbell Island: Unknown
Auckland Islands: Unknown
Their remote locations mean that pollution is unlikely to affect New Zealand rockhopper penguins. Ingestion of plastic and entanglement in plastic debris and abandoned fishing gear is possible, and likely to become more frequent, but is probably less likely for New Zealand breeding sub-Antarctic penguins than many other seabird species.
Establish consistent survey protocols for each of the three island groups
Networked autonomous operating time-lapse cameras can be used to monitor penguin colonies48,49 to cover periods between ground surveys.
Campbell Island surveys
A combination of Island-wide censuses during November in two consecutive years at random 3-6-year intervals, combined with annual counts at the accessible Penguin Bay colonies6,50, perhaps using time-lapse camera networks.
Antipodes Island surveys
A combination of Island-wide censuses randomly conducted every 3-6 years50, combined with annual counts at selected colonies perhaps using aforementioned time-lapse cameras. The last Island wide census was done in 2011 although some colonies were recounted in 2014. Establish photo points to document changes in areas utilised.
Map and census Auckland Island colonies
Most are on the almost inaccessible west coast. The use of camera drones may be an option51–53.
Priorities are age at first breeding, mortality at all life stages, recruitment into the breeding population, colony and mate fidelity. This requires annual visits and long-term observation of marked animals. This is highly desirable but logistically challenging, perhaps feasible at the Antipodes or Campbell Islands. Automated mark-recapture monitoring may be an option using implanted transponders and reader gates54.
Repeat photo-points on Campbell Island in November on two consecutive years at 3-6 year intervals using high resolution overlapping photos to count penguins27
There is no reliable trend data for the Auckland Islands.
The small colonies on the east coast are the easiest to access but trends there may not be representative of the larger inaccessible west coast colonies.
Taylor16 recommended analysis of the demographic data collected at Campbell Island on flipper banded birds, plus an assessment of the survival of penguins marked with flipper bands and those with transponders.
Foraging range using GPS devices during the breeding season at Antipodes and Campbell Islands
Ideally during all stages of the breeding cycle but most crucial is the chick rearing period. Female rockhopper penguins were tracked at Antipodes Island during guard and post guard stages December 2002- January 200336.
Satellite/GLS tracking of Campbell and/or Antipodes breeding penguins during the pre-moult period
Repeating such a study every 3-5 years will provide information about potential shifts in the ocean environment.
Satellite/GLS tracking of Campbell and/or Antipodes breeding penguins and, if feasible fledglings
Find out where they go between moult and breeding. Ideally, such a study would be conducted every 3-5 years.
Collect faecal samples for DNA analysis to determine prey composition55 at Campbell, Antipodes and Auckland Island colonies as opportunity allows. Animal-borne camera deployments may become an option in the near future56.
Influence of ocean warming
Investigate spatial and temporal links between population trends, prey abundance and oceanographic parameters including SST and primary productivity4.
Other oceanographic influences
Relate foraging ecology to Campbell Plateau oceanography in an attempt to understand why the species has declined so dramatically.
Stable isotope monitoring
Collect feathers and blood for stable isotope analysis as an adjunct to other research at Campbell, Antipodes and Auckland Island colonies when opportunity allows31.
Similar studies as above at the Auckland Islands are desirable but due to logistic constraints lower priority.
Breeding success, cause of breeding failure and timing of the breeding cycle at Campbell and/or Antipodes Islands.
Data on chick growth, meal sizes and fledgling weights at Campbell and/or Antipodes Islands.
Basic breeding parameters
The use of time-lapse cameras in obtaining data on the timing of the breeding season and other aspects of breeding biology should be explored. This feasibility study need not be done on rockhopper penguins.
Site & mate retention
Data on site and mate tenacity for rockhoppers at Campbell and/or Antipodes Islands.
Similar studies at the Auckland Islands are desirable but due to logistic constraints lower priority.
Sea lion impacts
More data on the impact sea lions may have on those Campbell Island rockhopper colonies also inhabited by sea lions is desirable.
Repeat the disease screening that was conducted at Campbell Island in 1988.
Thanks to Klemens Pütz, Kyle Morrison and Tess Cole for their comments on early drafts of this paper. Graeme Taylor reviewed the research priorities section of this review. Louise Chilvers and Jo Hiscock kindly allowed us to include observations of their paper currently in review. This review was kindly 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.