|Kerry-Jayne Wilson & Thomas Mattern||Document date: 12 April 2019; DOI: 10.36617/SoP.korora.2019-04|
Little penguins are widely distributed around North, South, Stewart and Chatham Islands, their offshore islands as well as southern Australia and Tasmania. At about 1 kg it is the smallest of the world’s 18 species of penguins and is currently considered by the 2017 IUCN Red List Assessment and Department of Conservation to be ‘least concern’ or ‘at risk declining’ respectively. Their numbers are believed to be declining in some parts of their range, are assumed to be stable elsewhere while increasing at a few locations. This is one of the best studied genera of penguins, but most of the research has been carried out in Australia, and largely at a single site, Phillip Island where a team of researchers work on Little penguins full time as part of a long term coordinated strategic plan in collaboration with universities and other research groups.
The breeding season of the little penguin varies region to region with robust information on timing and breeding success available for just a few New Zealand localities. Little penguins in most New Zealand populations lay a single clutch of two eggs each year, although Otago birds can lay twice each year and fledge chicks from both clutches.
Their breeding distribution is well known in general terms in both Australia and New Zealand but actual colony locations, the population size and population trends are poorly documented from most New Zealand sites. Many New Zealand colonies are small, some <10 pairs, although there are a few colonies of about 1,000 breeding pairs (e.g. Taieri Island, Motunau Island, Pohatu/Flea Bay). There are no large colonies as are found in Australia.
There is robust, long-term data on marine ecology for Australian populations but limited data for New Zealand. There is virtually no information on at-sea movements between breeding seasons.
Unlike other penguins, little penguins are nocturnal on land, coming ashore after dark and departing before dawn. Little penguins breed in burrows, caves or crevices, sometimes close to settlements. Burrow nesting is an extra challenge to overcome when researching them; much of the best research has been undertaken in places where the birds use artificial nest boxes.
Despite the extensive and intensive research carried out in Australia, this is of limited use when it comes to addressing conservation needs in New Zealand. The little penguin is perhaps more plastic in its ecology than other penguin species. Demography, breeding biology, timing of the annual cycle, fledgling success, foods and foraging ecology; all aspects of a species’ biology that are important when it comes to conservation management, vary region to region and even year to year. Further research at multiple sites is required into all these aspects of their ecology.
During the breeding season little penguins generally feed within about 20 km of their colony although tracking studies show that at some sites penguins may fed much further offshore. It is assumed they travel further between breeding seasons, although there is no New Zealand data to confirm this. The penguins from Australian research sites forage in very different marine environments from those utilised by New Zealand penguins, and ashore are exposed to different predators and climates. Furthermore, the Australian birds perhaps belong to a different taxon than those inhabiting most of New Zealand.
Little penguins are subject to numerous threats both on land and at sea. Ashore the main threats include dogs (Canis familiaris), road-kill, introduced predators, coastal development and disturbance from people. Marine threats include entanglement in fishing nets, changes in food availability due to fishing, climate change and ocean warming. Threats vary from region to region, although most information available is anecdotal and there have been few attempts to quantify threats.
Conservation needs may differ region to region necessitating regional or population level management. Only a comprehensive, investigative approach will allow us to understand factors driving declines and identify and enact the management actions required to reverse declines of Little penguins in different parts of New Zealand.
Here we review the current knowledge of this species in New Zealand, identify gaps in our knowledge and research priorities required to allow evidence-based conservation of the species. We use the name little penguin to refer to all members of the genus Eudyptula and present here information on all New Zealand Eudyptula populations. As the location of each study cited is given, it should be simple to assign information to a species/sub-species once the taxonomy is finally resolved and the geographical limits of the proposed Australian/Otago taxa determined.
There are numerous books on penguins catering for both the scientific and popular markets and most have sections devoted to little penguins (among the best are Davis & Renner1 and the three chapters on little penguins in De Roy, Jones & Cornthwaite2); most use information from Australian studies with the implicit assumption that things will be similar in New Zealand. The account in Marchant & Higgins3 is the most encyclopaedic including snippets of information from all parts of their range. A concise summary of the status of the species and the basis for this appears in BirdLife International4. The best recent review of current knowledge is by Peter Dann5, based mostly on his many years working with little penguins at Phillip Island in Australia. His account is Australian focused and, while an excellent overview, lacks the detail on New Zealand populations required here. In this review we focus on information obtained from New Zealand.
Forest and Bird reviewed the status of all New Zealand penguins and that document presents an overview of the status, research priorities and conservation of the little penguin6. Other descriptions of New Zealand little penguin populations such as Flemming[[7 were written primarily for the lay person and provide rather brief introductions to the species.
The most detailed list of research and management priorities is that by Graeme Taylor8,9 who considered each of the five then recognised sub-species of little penguin that bred in New Zealand separately. Eighteen years later few of those priorities listed by Taylor have been addressed. Peter Dann5 lists some research priorities, but, this is primarily Australian focused. BirdLife International4 includes a short list of conservation actions required for little penguins relevant to both New Zealand and Australia.
The Department of Conservation lists the little penguin as ‘at risk -declining’10 and the IUCN Red List as ‘least concern’ 4. Both organisations recognise a single species with no sub-species. The status of the New Zealand taxon is likely to change if two species/sub-species were recognised.
The taxonomy of the genus Eudyptula urgently needs to be resolved. Kinsky & Falla11 recognised six sub-species all within a single species. These were the northern blue penguin (Eudyptula minor iredalei) (North Island, north of Kawhia in the west and East Cape on the east coast); Cook Strait blue penguin (E. m. variabilis) (North Island; south of Cape Egmont and Hawke Bay, South Island; Nelson and Marlborough); southern blue penguin (E. m. minor) (South Island, West Coast, Southland , Stewart Island and Otago); white-flippered penguin (E. m. albosignata), (Banks peninsula and Motunau Island); Chatham Island blue penguin (E. m. chathamensis) (Chatham Islands) and the Australian blue penguin (E. m. novaehollandiae) (New South Wales to Perth across southern Australia). These six subspecies were recognised by Davis & Renner1 and Taylor8,9 despite the official checklist of New Zealand birds12 and Marchant & Higgins3 recognising just a single taxon. The current Ornithological Society checklist recognises a single species Eudyptula minor with no subspecies13.
A study comparing mitochondrial DNA from all six putative sub-species found an unexpected pattern of molecular divergence14. The molecular data showed the Australian and Otago birds to belong to a single clade (Australian little penguin), distinct from all other New Zealand birds (New Zealand little penguin). The separation of New Zealand and Australian little penguins was further supported by Peucker, Dann & Burridge15 and Waugh16 using DNA barcodes, although Waugh did not include Otago birds. Variation within the New Zealand clade gave some support for the Kinsky & Falla11 classification, although this was equivocal14 and not supported by Waugh16.
To test this unexpected divergence, vocalisations and morphological traits from four of the Kinsky & Falla sub-species were compared14. Measurements showed that the Australian and Otago birds were similar to one another, and that while Southland, Stewart Island and West Coast birds were similar to one another, they differed from Otago penguins. Comparison of vocalisations provided some evidence to support the separation between Australian/Otago and New Zealand birds but it was not conclusive14. A subsequent study found little variation in little penguins across southern Australia and in Otago, with further evidence to support this clade as distinct from those in the rest of New Zealand17 with little gene flow18 between the two taxa.
More recently, Grosser et al.19–21 used morphological, behavioural and genetic data to provide further support for the distinction between the two taxa, albeit with low levels of interbreeding. They used mitochondrial control region, mitochondrial cytochrome oxidase 1 (COI) and microsatellite markers22, which are genetic markers commonly used to assess species-level distinctions and population structure in birds23,24. Grosser et al.19 genotyped little penguins from numerous sites across New Zealand and Australia. In Australia, only Australian genotypes were detected. Concordant with Banks et al.14, this Australian lineage was also detected on the Otago Peninsula and at Oamaru where a few New Zealand clade birds were also found. Elsewhere in New Zealand, including the Chatham Islands, the vast majority of individuals were the New Zealand clade, with just a few Australian-clade birds present, except in the Bay of Plenty and Auckland regions, where only the New Zealand clade was detected19. The divergence within the control region (10–14%) between the New Zealand and Australian lineages is similar to the divergence between Spheniscus penguins (8–10%), and for the COI gene is 3.8%, much higher than 0.8% between African (Spheniscus demersus) and Magellanic penguins (S. magellanicus), and 1.5% between southern (Eudyptes chrysocome) and northern (E. moseleyi) rockhopper penguins19. Cole et al. 25 constructed a phylogenetic tree of all penguins using COI which also supported two distinct Eudyptula species. Grosser et al.19 cite further evidence for recognising two species, including plumage, vocalisation and behaviour. For example, only Australian and Otago penguins ‘raft up’ offshore and come ashore in groups, whereas New Zealand birds usually land singly. Moreover, only Australian and Otago birds relay after fledging young from their first clutch.
Grosser, Scofield & Waters21 made a total of 65 measurements of bones from little penguin skeletons collected from numerous sites around New Zealand and southern Australia. Little penguins from southern New Zealand were larger than those from northern New Zealand, and the authors suggest that body and bill sizes could be inversely correlated with sea surface temperature. However, little penguins in Australia inhabit warmer seas, yet have a larger body size than those in New Zealand5, even if it is only slight21. Despite this minor variation they detected consistent differences in the osteology between the New Zealand and Australian/Otago clades21. For most measurements Australian birds were slightly larger than New Zealand birds but very similar to those from Otago. Although they did not find any single element that was noticeably different between the two putative species, the sum of subtle differences between the Australian/Otago and New Zealand regions supported recognition of two species of Eudyptula penguins.
Grosser et al.19,20 suggested that the little penguins originally in Otago, which were of the New Zealand genotype, became locally extinct following Maori settlement, to be replaced by Australian little penguins sometime between AD 1500 and 1900, not during the late Pleistocene as suggested previously. Holocene fossil Eudyptula bones and those found in prehistoric middens were carbon dated and genotyped by Grosser et al.20 who found that all ancient bones thus sampled from Otago were of the New Zealand taxa, whereas almost all living and post AD1900 penguins sampled from Otago belonged to the Australian/Otago taxa. Little penguin bones occur in pre-historic middens dated between AD1280 and 1650, but are absent from midden sites accumulated since AD1650, indicative of local extinction about 165020.
The methods applied by Banks et al.14, Overeem et al.18, Peucker, Dann & Burridge15, Grosser et al.19,20, Waugh16 and Cole et al.25 provide critical evidence for two clades of little penguins, yet these clades have not yet been formally recognised as distinct taxa. Grosser et al.19 recommended that the New Zealand and Australian/Otago little penguin clades be elevated to separate species, the New Zealand taxa as Eudyptula minor and the Australian/Otago clade as E. novaehollandiae.
The white-flippered penguin which is restricted to Banks Peninsula and Motunau Island is no longer recognised as a distinct taxon13,19. However, it is morphologically distinct from other little penguins and may warrant separate conservation management.
Tobias et al.26 use phenotypic and ecological differences for their definition of species, omitting molecular data arguing that there is no consistent correlation between genetics and phenotype, and it is the Tobias score that is favoured by Birdlife International and the IUCN in determining species status. To ultimately address the taxonomic status of the Eudyptula taxa a comprehensive study of the phenotypic characteristics differentiating the various little penguin populations is required to assess whether molecular differences described above reflect ecological differences.
Little penguins occur around most of New Zealand27 but systematic surveys of their distribution and abundance have been carried out for few parts of this country. A comprehensive list of all known Little penguin colonies in New Zealand has been compiled by Kerry-Jayne Wilson in 201928. Unless otherwise cited, the information in this section and the following section comes from the resulting colony list.
Little penguin colonies occur around much of Stewart Island but there have been no comprehensive surveys in the Stewart/Foveaux Region. There may be up to 1,000 Little penguins on Codfish Island/Whenua Hou (T. Mattern, own observation). Little penguins occur in southern Fiordland but colonies there have not been mapped or counted.
In Otago, the coast from the Waitaki River south to Nugget Point was searched on foot between October 1991 and February 1992 and counts made at all the little penguin colonies located29. In all, a total of 2073 breeding pairs were counted from 20 different colonies; most colonies were small, only four, Oamaru (218 pairs), Taiaroa Head (128 pairs), Green Island (223 pairs) and Taieri Island (1,338 pairs) supported more than 100 pairs. Between them these four colonies accounted for 97% of the total number of pairs found29. The survey has not been repeated although those colonies in and near Oamaru and those on Otago Peninsula have been revisited.
A survey of Little penguin colonies on Banks Peninsula between 2000 and 2002 located 68 colonies of which 51 contained 5-20 active nests and just five had >50 active nests; the largest at Pohatu/Flea Bay with 717 nests30. Forty other sites had fewer than five nests. Penguin colonies were found around the entire Peninsula with 72% of colonies located along the Peninsula’s eastern coast. Challies & Burleigh30 estimated the total Banks Peninsula population to be 2,112 active nests, four times that of a previous estimate, although the difference is almost certain to reflect survey effort rather than any increase in numbers. Coupled with the estimated 1,650 nests on Motunau Island this makes a total of about 10,460 birds of the white-flippered form of the little penguin30. Only Pohatu/Flea Bay and Stony Bay have been resurveyed since, both these colonies have increased (F. Helps unpublished) although this is unlikely to be typical of other Banks Peninsula colonies.
The West Coast Penguin Trust has surveyed Little penguin colonies along much of the South Island West Coast31,32. The initial survey consisted of observers walking along about 400 km of coast between the Heaphy River and Jackson Head noting any sign of penguin presence. This was followed up by intensive searches of those areas where penguins appeared most common. The initial walk through survey proved more accurate than might be expected; some colonies were missed but the overview of penguin distribution it gave has proven useful. The West Coast Penguin Trust continues to survey or revisit sections of the coast as land development, new threats, coastal erosion or other circumstances require. Data accumulated since 2008 are on file but not published. On the West Coast, penguin presence is discontinuous with large areas of suitable habitat apparently not used31. Most colonies are small, the largest only 30-40 pairs. The main concentrations appear to be in the Buller Region (Buller River to Punakaiki) and near Okarito with colonies on the urban fringes of both Hokitika and Greymouth (Blyth et al. 2008, Braidwood, Kunz & Wilson, 2011, WCPT unpublished). Little penguins appear to be scarce south of the Waiho River (Franz Josef).
Little penguins breed on islands and in some mainland localities in Nelson and Marlborough but there has been no systematic mapping of their distribution and few colonies have been censused.
There appear to have been few systematic surveys of little penguin distribution on the North Island, although many colonies are known and at a few numbers have been estimated. Most known colonies are in the Northland, Hauraki Gulf and Coromandel areas with fewer recorded colonies in the Bay of Plenty, Hawkes Bay and Wellington. On the West Coast of the North Island there are small colonies in Taranaki but few elsewhere. Little penguin colonies in the Mount Maunganui area have been surveyed by Winter34.
On the Chatham Islands Little penguins are known to nest on Chatham, Pitt, Rangatira, Mangere, Star Keys, Houruakopara and Kokope Islands but there are no estimates of numbers for any of these islands.
The total number of little penguins including both New Zealand and Australian birds is estimated to be around 470,000 mature individuals with perhaps about 64,700 of those in New Zealand; previous estimates based on anecdotal information had suggested about 1 million individuals35. Based on a comparison of colony counts made prior to and since 2000, an increase in numbers was suggested35. However, for New Zealand this apparent increase is more likely to reflect increased survey effort rather than an increase in penguin numbers. For instance, on the West Coast, the Birdlife assessment includes 2,420 penguins counted since 2000 whereas only 1530 were counted prior to that date, yet colony monitoring in that region indicates a slow decline with some small colonies lost in the last decade31 (also R. Lane and K-J. Wilson, unpublished data). Some regional estimates used in the Birdlife estimate are simply wrong, for instance, at the Chatham Islands, the pre-2000 number was just 350, whereas the post-2000 estimate used was 20,350. In reality there were more than 350 but far fewer than 20,350; Aikman & Miskelly36 estimate there to be 5,000-10,000 pairs, with the lower end of this range perhaps being most likely (D. Houston pers. comm.).
In New Zealand Little penguins are thought to be in decline but there is little robust data on population trends. A survey of Little penguin distribution in 1991-92 failed to find penguins at seven sites in Otago where Little penguins had bred prior to 1990 and found far fewer little penguins on Otago Peninsula than comments by Lance Richdale suggested were present in the 1930s29. Numbers on Green Island had declined from an estimated 1,500 pairs in 1983-84 to an actual count of 223 pairs in 1991-92, noting though that the earlier estimate was less accurate than the later count29. On Otago peninsula 11 of the 29 breeding sites found in the 1970s had been extirpated by 1994, although the total number of penguins breeding on the Peninsula increased; numbers rebounding in those colonies with predator control, with the greatest increases in colonies where nest boxes were also provided37.
In those Oamaru colonies protected from dogs and other predators, penguin numbers have increased. At the Oamaru Blue Penguin Colony numbers of breeding pairs increased from 33 in 199338 to 160 in 2010, dropping back to 145 in 201139.
Little penguins were very common on Banks Peninsula in the late 19th and early 20th centuries but since then numbers have declined markedly30,40. Penguins disappeared from the heads of most bays, particularly those with human habitation, by the 1950s or early 1960s, and from most other colonies accessible to predators during the 1980s and 1990s40. Numbers in monitored colonies on Banks Peninsula declined by 83% between 1981 and 2000, except in areas where feral cats (Felis catus) were the dominant predators30,40. The declines in the 1980s coincided with an increase in ferret (Mustela furo) and rabbit (Oryctolagus cuniculus) numbers following changes in rabbit control during the 1970’s. Ferret numbers on Banks Peninsula declined after 2000 allowing some recovery in the penguin population40.
Population demographic modelling may provide important insights into the effective population sizes, and provide a window to understand past, present and future population trends of little penguins under different scenarios. Population genomic information may also be important for identifying which management units41 within little penguin populations, may require particular conservation management.
Two papers42,43 provide information on how to sex Little penguins from external measurements.
Little penguins first breed when 2-3 years old5. On Otago Peninsula four of 42 known-age birds first attempted to breed when only one year old and 25 when two years old37. They do not tell if those first attempts were successful.
Annual survival can only be calculated during long-term studies with marked birds. Over 19 years adult little penguins in Oamaru had an annual survival of 0.86 (SE = 0.02), first year birds 0.42 (SE = 0.03) and second years 0.82 (SE=0.03, Agnew et al., 2016). Annual survival of breeding penguins was not affected by age although breeding birds had a higher survival rate than pre-breeders of the same age44. A study following banded birds month by month found that the eight-week survival during moult, post-moult and midwinter was significantly lower than that during the breeding season, with the lowest survival rate occurring during the post-moult period (eight-week survival probability 0.88)45.
In the only systematic study of mortality factors for little penguins in New Zealand Hocken46 necropsied 213 Little penguins found dead in Otago between 1994-1998 (Table 1). In that paper he describes in detail the diagnostic features used when attributing the cause of death and any one undertaking a similar study should consult that paper.
|Cause of death||Otago46||West Coast|
|Unknown||32 (15%)||62 (20%)|
|Starvation/beach stranding||34 (15.9%)||31 (10%)|
|Road kill||22 (10.3%)||168 (54%)|
|Railway kill||8 (3.75%)|
|Unspecified trauma||20 (9.4%)|
|Predation by dog||30 (14%)||41 (13%)|
|Predation by cat||1 (0.3%)|
|Predation by mustelid||20 (9.4%)||3 (1%)|
|Predation by shark/other fish||8 (3.75%)|
|Unspecified predation||5 (2.3%)|
|Killed by human||10 (4.7%)||1 (0.3%)|
|Killed in predator traps||3 (1.4%)|
|Killed by fur seal||3 (1%)|
|Coastal development||1 (0.3%)|
In Hocken’s46 study the only species of mustelid known to prey on penguins was the ferret; stoats (Mustela erminea) were present though rare in his study area. Mustelids posed a greater threat to penguins in Otago than on the West Coast where ferrets were absent. He assumed those birds that drowned were caught in fishing nets, then thrown overboard before washing up in Oamaru.
The West Coast Penguin Trust in collaboration with DOC maintains a penguin mortality data base on which is recorded the date, location and if possible the cause of death of all little penguins reported dead on the West Coast. Between August 2000 and April 2018, 311lLittle penguins were found dead and the likely cause of death is shown in Table 3. Road kill was the major cause of penguin deaths on the West Coast with most kills on just a few kilometres of coastal highway. Penguin-proof fences were built along the 3.3 km of highway where most deaths occurred. There have been no road kills in areas thus protected, although road kill remains an issue elsewhere. Dogs are the other major cause of little penguin deaths on the West Coast and Otago as they are in other urban and rural locations around New Zealand.
These studies of mortality factors are highly biased. The probability of a road-killed penguin being reported is much higher than one drowned in a fishing net; one killed by a dog more likely to be reported than a penguin killed by a shark or ferret, and those in urban areas more likely to be reported than any killed in rural areas let alone those from remote colonies.
There are periodic wrecks when large numbers of little penguins are found washed up on beaches but there have been few attempts to assign a cause of death to beach-cast birds. Wrecks may occur anywhere around New Zealand but seem to be particularly frequent with larger numbers killed in Auckland/Northland than elsewhere47. The cause of death of some of the 1,648 penguins found on Northland Beaches in July, August and December 1973, and 3,649 found between January and July 1974 was reported by Crockett & Kearns48. All birds examined were young with more females than males being found. All showed wasted musculature, deplenished fat reserves, empty intestines and high parasite loads48. The cause of death appeared to be exhaustion and starvation, accentuated by high parasite loads and rough seas48. Those birds tested had insignificant levels of heavy metals, organochlorines or polychlorinated biphenols.
Little penguins generally return to breed at their natal colony. There are few estimates of the percentage that breed in colonies other than those in which they were born, or for those birds the distance between natal and breeding colonies. Of 3,970 fledglings banded in the Oamaru Blue Penguin Colony, 19 subsequently bred at the Oamaru Creek Colony 1 km away49. Thirty-one penguins (19 females, 12 males) had been banded elsewhere in Otago but bred at the Oamaru Blue Penguin Colony; 28 of which were banded at other Oamaru colonies and three at Taiaroa Head 80 km distant49.
Little penguins tend to retain their pair bond and nest in the same burrow year after year. There is good data spanning multiple years from Phillip Island in Australia where 76% of female penguins and 79% of males returned to the nest they used the previous year50. In Australia divorce rates varied from 0-40% each year with pair bonds lasting 1-13 years with little penguins having on average 1.8 mates during their life time50. Those that bred successfully had a higher probability of nest and mate fidelity than those that failed to raise chicks.
The data from New Zealand are less robust. At Taiaroa Head, Otago Peninsula, little penguins were monitored for five consecutive years in two colonies either side of the headland (1 km apart as the penguin swims)51. None of the 187 penguins in their analysis moved from one colony to the other. Nest fidelity from one year to the next was 72% (69-79%) and pair fidelity 82%, differing between the two colonies and between nest boxes and natural burrows51. Nest fidelity was higher for pairs that bred successfully the previous year and for those that retained the same partner. The probability of moving from one nest to another was higher than that of changing partners, with females just as likely as males to return to the same nest51.
During a two-year study on Matiu/Somes Island, Wellington, of 29 pairs banded in 1995, the pair bond is known to have remained intact for 12 pairs, but only eight pairs used the same nest a year later52. In only two of those 29 burrows was one bird known to breed with a different partner in 1996 than in 1995, for the remaining burrows the 1996 partner was not identified, or the pairs not located52. Of the 74 nests located in that study only 15 were used both seasons52.
Little penguins usually breed in colonies with the distance between nests determined by terrain and substrate. A few pairs nest solitarily which may be the last survivors of once larger colonies. Colony size varies from less than 10 pairs to over 1000 pairs.
Terrain and substrate include sand dunes, talus slopes, coastal forest and rocky coasts, the only requirement appearing to be substrate which allows burrows to be dug, or the presence of natural crevices, tree roots or caves which allow the penguins to find a dark place to nest. The penguins will nest on breakwaters, under buildings, in culverts, or beneath other structures. Little penguins breed in some urban areas including harbour-side suburbs in Wellington city and Oamaru.
Figure 1. Little penguins breeding sympatrically with Yellow-eyed penguins on Green Island, Dunedin (Composite of photos by Thomas Mattern).
Little penguins will breed in artificial nest boxes particularly where natural sites are limiting. The standard nest box (http://www.doc.govt.nz/Documents/conservation/native-animals/birds/nest-box-design.pdf) needs to have an entrance tunnel at least 50 cm long in areas where weka (Gallirallus australis) are present. Concrete nest boxes have been used in public areas to prevent interference by people.
Nests are a collection of sticks, twigs, leaves and other material including plastic and other debris found close to the burrow entrance.
Nest density and nest type has seldom been quantified in New Zealand and probably reflects substrate and terrain more so than penguin preference. On the West Coast, nest density of both available and occupied nest sites was higher in the Buller Region (0.25-0.45/100m2 and 0.13-0.21 /100m2 respectively) than in South Westland (0.003-0.01 /100m2, 0.002-0.006/100m2) with density tending to be greater <25 m from the shore than >25 m from it53. In South Westland the penguins nested in scrub and low forest spread along the length of sandy beaches, whereas in the Buller penguins nested on rocky coasts where colonies were bounded by cliffs, rivers and roads53.
As with all seabirds bi-parental care is required to incubate eggs and raise chicks. A good concise account of the breeding cycle appears in Dann5 and an introduction to the challenges facing little penguins while breeding by Chiaradia54. Breeding biology has been studied in greater detail in Australia than in New Zealand, here we only review those studies carried out in New Zealand. The most detailed account of the little penguin breeding cycle and chick development in New Zealand is by Kinsky55 which contains details from very frequent inspections at all stages of the annual cycle. Both parents spend about five days together in the nest about a month before egg laying. For the next month both are at sea, the male returning a day or two before, or on the same day as the female, and they remain together at the nest until the first egg is laid. The mean interval between laying first and second eggs is 2.8 days1. During incubation the parents alternate with stints of 1-10 days where one is ashore incubating the eggs while the other is feeding at sea.
The date ﬁrst eggs were laid at Oamaru during 19 breeding seasons ranged from 2 May in 1996 to 30 September in 1999, with a median date of 17 July, the first pair to lay often laying a month before any others39. One or other parent remains with the chicks for the first two to three weeks after hatching1; the length of this guard stage being variable, reflecting foraging success. After that chicks are left alone in the nest, both parents returning to feed them every 1-2 days, less often when food is scarce. Breeding success varies year to year; in good years some pairs can fledge both chicks, whereas in poor years few pairs manage to raise even a single chick to independence.
Little penguins usually lay two eggs per clutch, about a quarter of clutches comprised a single egg and of 167 clutches observed, three contained three eggs55. The three egg clutches probably a result of two females laying in the same nest. Australian little penguins and at least some of the Otago population can lay two clutches per year and successfully rear chicks from both (double brooding)5,39. On Otago Peninsula 48% of pairs laid a second clutch after successfully fledging at least one chick in 1993, whereas none did in 1998 when breeding began much later in the year56. In Oamaru double brooding occurred in >10% of pairs during 12 of the 19 study years, double brooding being more likely in seasons when breeding began early in the year, and only by those pairs that laid their first clutch prior to mid-September39. Experienced breeders were more likely to lay early thus, lay second clutches.
Double brooding regularly occurs only with Australian and Otago penguins, suggesting double clutching is characteristic of the Australian/Otago clade. Rare instances of double brooding have been reported from New Zealand clade birds in Oamaru, (P. Agnew pers. comm.), at Kaikoura (L. Rowe pers. comm) and at Pohatu/Flea Bay, Banks Peninsula (F. Helps pers. comm.).
Elsewhere in New Zealand Little penguins lay a single clutch53,57–59. On Matiu/Somes Island, Wellington, about 10-11% of failed breeders re-nested after their first clutch was lost, but never after chicks had fledged successfully52,55,60. In those Wellington studies the date of laying had no effect on breeding success59.
The incubation period is 35-39 days (Table 2) but can be as long as 43 days if the eggs were left unincubated for several days55.
|Location||Incubation period [days]||Chick rearing period [days]||Reference|
|Otago||36 (33-39)||54 (48-59)||Marchant & Higgins[[3|
|Charleston, West Coast||34 (30-38)||58 (48-64)||Heber[[57|
During incubation feeding trips, thus incubation spells, were about twice as long at Motuara Island (outer Marlborough Sounds) than Oamaru61, although most feeding trips during the guard stage were one day, seldom two days, at both places62. The guard stage lasted longer at Oamaru than at Motuara Island and was longer for single chick broods than for pairs with two chicks to feed. Parents with two chicks lost more body condition than those with a single chick62.
Breeding success at Taiaroa Head varied greatly year to year and from one part of the Headland to another (Table 3), the lowest recorded breeding success (23%) was in one small sub-colony where one season some nests were flooded56.
|Location||Year(s)||Hatching success*||Fledging success*||Breeding success*||Chicks fledged / pair||No. seasons||Reference|
|Taiaroa Head, Otago Peninsula||1992-1998||40-81%||58-95%||23-78%||7||Perriman[[56|
|1993-1997||Colony A, 1.64 (1.09-1.87)
colony C, 1.12 (0.94-1.18)**
|Charleston, West Coast||2006||78.9%||83.9%||66.2%||1.8||1||Heber[[57|
|Pohatu/Flea Bay, Banks Peninsula||1996-2009||75% (58-83%)||85% (68-97%)||64% (53-80%)||1.29±0.84||13||Allen[[66|
|*Hatching success was defined as the proportion of eggs that hatched relative to the number of eggs laid. Fledging success is the proportion of chicks that fledged relative to the number of chicks that hatched. Breeding success was defined as the number of chicks that fledged relative to the number of eggs laid.
**Some pairs in these populations laid two clutches per year.
The ways environmental factors affect breeding success in Little penguins and how the birds cope with environmental variability has been studied in much greater detail in Australia than in New Zealand; see Chiaradia54 and Saraux et al.67 for introductions into the Australian research. In New Zealand a study of factors affecting breeding success was conducted over 13 years at Pohatu/Flea Bay where breeding success was measured relative to 21 variables spanning biological, climatic, predator abundance and nest factors66. They found that breeding success was significantly greater when the guard period was longest, average pair bond length shorter, and lay date later66, the effect of the latter two variables being counter to some other studies. The length of the guard period was the strongest predictor of breeding success, both presumably influenced by food availability. Lay date was the only variable that was significantly related to hatching success and none of the variables examined predicted fledgling success66.
There have been few attempts in New Zealand to relate breeding success to climatic factors. Over a five-year study in Otago, Perriman et al.38 found that when La Niña conditions prevailed (warmer than average ocean temperatures), penguins started breeding later, leaving insufficient time for most pairs to lay a second clutch, than in El Niño (cooler waters) and normal years. The probability of a newly hatched chick fledging was influenced by these large-scale climatic conditions, whereas hatching success was not correlated with climate perturbations38.
The timing of the breeding season of little penguins is highly variable both year to year and within New Zealand region to region. At Oamaru the breeding season can range from May to January but in most parts of the country laying generally occurs in August and September39,55,57,59.
Gales68 studied the growth of chicks on Otago Peninsula and compared Otago chicks with chicks elsewhere. That paper includes growth curves that allow chicks to be aged. Other sources of information on chick growth are Mattern64 and Numata et al.62.
Figure 2. Little penguins moulting (Photo: Brent Tandy, Department of Conservation).
The annual moult is the most stressful and energy demanding time in a penguins’ year, yet there is little data on the timing and duration of moult in New Zealand little penguins. The most detailed description of moult is by Kinsky55.
In New Zealand little penguins moult between December and March55. In Wellington the duration of moult was on average 15.5 days (12-18) with the loss of 40-50% of their pre-moult weight60. In Otago moult lasted on average 16.2 days (15-18)3.
Non-breeders and failed breeders usually moult before penguins that bred successfully, many birds moulting in the colony in which they bred. On Matiu/Somes Island 20% of banded birds moulted in the burrow in which they bred, several birds moulted in the same burrow, sometimes even simultaneously, and that the sites best suited for breeding were not always those preferred for moult55.
Little penguins have a generalist diet mostly taking small nearshore pelagic, schooling fish with lesser reliance on cephalopods and krill (Australian data reviewed by Dann5, for New Zealand see Fraser & Lalas69, Flemming et al.70). Their diet varies regionally and seasonally presumably reflecting prey availability.
|Codfish Island/Whenua Hou||1984||97%||98%||3%||1%||-||-||van Heezik[[71|
The most detailed study of little penguin diet in New Zealand is a year-long study at Oamaru which identified a total of 22 prey species (Table 5)69. Fish dominated, occurring in 89 of the 90 penguins sampled, accounting for 90% of the estimated prey mass (Table 4).69. Cephalopods occurred in only 21 samples and made up about 10% of the prey mass; the few crustaceans found included fish ectoparasites, presumably ingested along with their hosts69. The most commonly taken prey species was slender sprat which was recorded in all 10 months when samples were obtained, and over the course of the study comprised 75% of prey biomass. Of the 22 prey species (Table 5), just four others were commonly eaten, these being; Graham's Gudgeon, arrow squid, southern pigfish and common smelt69. Most prey were estimated to be 15-100 mm in length.
|Prey type/species||Stewart Is./Rakiura (2010)||Codfish Is./Whenua Hou||Oamaru (1994-95)||Oamaru (2010)||Banks Peninsula (2010)|
|unidentified Mysid krill||<1%|
|Unidentified planktonic amphipod||<1%|
Van Heezik71 studied the diet of little penguins at Codfish Island/Whenua Hou in October 1984 and compared their diet with that of tawaki (Eudyptes pachyrhynchus) and yellow-eyed penguins (Megadyptes antipodes) on the same Island. Arrow squid made up 58% of little penguin diet by weight but comprised only 2% of the individuals caught. Ahuru was the most commonly recorded prey (88% of prey items) but comprised only 37% by weight of food taken. The other species recorded (Table 5) were rare constituents of the diet71. Fish taken by little penguins were generally post-larval and juveniles, <50mm long, the squid being <10 gm. Most of the food taken in this study were pelagic macro-zooplankton71.
In November-December 2010 little penguins were sampled at Banks Peninsula, Oamaru and Stewart Island70. They identified 12 prey species (Table 5). Arrow squid were present in about 90% of samples at all three sites; being the most important prey at Stewart Island where they made up 73.1% of the food by mass, compared with 14.6% on Banks Peninsula and just 4.8% at Oamaru (Table 4). Of the 10 fish species found (Table 5), Graham’s Gudgeon was the most important at Oamaru (present in all samples and over 91% of diet by both number taken and prey mass) and ahuru the most important at Banks Peninsula (in 75% of samples, 59.3% by number and 37.4% by mass). At Stewart Island, red cod and slender sprat occurred in over half of the samples but made up just 8.8% and 10.4% respectively of prey mass70. The other fish species were uncommon prey (Table 5). Tiny stomatopod larvae were only found in Stewart Island samples; although they were found in over half of the 22 samples obtained there, they made up just 5.5% by mass but 85% of the prey items recorded from Stewart Island70. Excluding the stomatopod larvae, mean prey length varied from 62 mm for red cod at Stewart Island to 169 mm for slender sprat at Oamaru, and mean prey mass 3 g for red cod at Stewart Island to about 60 g for slender sprat at Oamaru and Banks Peninsula70.
Stomach flushing, the method used in all of the above studies provides a biased snapshot of diet, reflecting the food taken in the previous days. Furthermore, some foods are digested faster than others. For example, cephalopod beaks are likely to be retained in the stomach longer than many fish otoliths. Stable isotope ratio analysis (SIA) of carbon and nitrogen in feathers and blood provide information on diet over longer periods. SIA can provide information on the trophic level targeted and whether fish, cephalopods or crustaceans, were eaten, but do not generally distinguish between actual species. SIA is based on the predictable and quantiﬁable ways that tissue nitrogen (δ15N) and carbon (δ13C) isotopes change at different trophic levels in the food chain. Isotope levels in blood reflect the food taken during the last 28 days, whereas those of feathers indicate food obtained prior to the moult.
Flemming & van Heezik72compared the diet of little penguins as determined using SIA with that estimated by stomach flushing[[70 (see above) using the same penguins at the same sites. Feathers from little penguins on Stewart Island had lower δ15N than those at either Oamaru or Banks Peninsula. Feathers from Oamaru penguins had lower δ13C than those from either Banks Peninsula or Stewart Island, with no significant differences found between feathers from Stewart Island and Banks Peninsula penguins72. Isotopic mixing models for feathers, indicated that ﬁsh made up the major part of the diet for birds that later bred at Oamaru (46.4%) and Stewart Island (62.3%), but to a lesser extent those that subsequently bred at Banks Peninsula (35.4%). Cephalopods comprised a third to a half of the pre-moult diet of penguins from all three sites72.
Isotopic mixing models for blood estimated that cephalopods and ﬁsh made up 49.9% and 33.8% respectively of diet at Oamaru, at Banks Peninsula fish (46.3%) and cephalopods (46.8%) were taken in approximately equal amounts, whereas at Stewart Island, crustaceans (77.2%) dominated the diet72.
SIA when compared with stomach flushing indicated that stomach content analysis under-estimated the importance of squid and crustaceans and overestimated the proportion of ﬁsh in the diet72. SIA of blood suggested that little penguins from Oamaru and Banks Peninsula fed at higher trophic levels than penguins at Stewart Island, where field observations show little penguins feeding very close inshore (T. Mattern, unpublished data). SIA of feathers indicated that Stewart Island penguins were feeding at a lower trophic level during the pre-moult period than penguins further north, and those from Oamaru feeding further offshore than little penguins at Stewart Island or Banks Peninsula72.
Stable isotope ratios of little penguins breeding on Motuara Island, outer Marlborough Sounds, indicated that during incubation penguins fed on a broader range of offshore-dominated prey compared with birds rearing chicks which took a narrower range of prey from higher trophic levels; reflecting the longer duration feeding trips made during incubation than during chick rearing73.
Genetic information derived from scat samples can provide information of the diets of penguins74, that may be overlooked by more conventional approaches. This is non-invasive, and a single sample can provide information about the individual, including genotype, sex, bacterial communities, pathogens and parasites. Any study wishing to use 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.
There have been extensive studies of the foraging ecology of little penguins in Australia with fewer studies in New Zealand. The most thorough study of foraging ecology in New Zealand was conducted in Oamaru by Agnew75 who during 2010, 2011 and 2012 deployed GPS units a total of 241 times on 22 different individuals and conducted 135 successful deployments of time depth recorders (TDR) on 26 individual penguins. Deployments occurred during all stages of the breeding cycle for birds with both first and second clutches. Dive depth tended to decrease with each subsequent stage in the breeding season, whereas the number of dives per day tended to increase75. Mean dive depth was greatest (12.67 m, SE: 0.45 m) while feeding their first brood of chicks in 2010, and least (5.06 m, SE: 0.28 m) while rearing their second brood in 201275. The number of dives per day peaked at 1,264 (SE: 151) when rearing the second brood of chicks in 2010. Dive depths were shallowest, averaging just 5-7 m, in December and January64,75.
Oamaru little penguins generally fed in waters <50 m deep and <20 km from shore, and on single day trips usually remained within 20 km of their colony75,76. Penguins travelled further during incubation than during chick rearing; all two-day trips occurred during incubation and mostly to places north of the Waitaki River75. While breeding the furthest point from the colony reached by an Oamaru penguin on a single day trip was 35.2 km north of the colony by a penguin rearing a second brood. Penguins tended to travel further and stay at sea longer during stormy weather75.
A multi season, multi-site study using GPS in central New Zealand73 bought together tracks made during the breeding season in Wellington Harbour (2011, 2012, 2014), Motuara Island, outer Marlborough Sounds, (2014, 2015) and the Buller Region, (2013, 2015, 2016). All three sites are within a single latitudinal band with contrasting offshore marine environments. There was considerable variation between sites. Wellington penguins mostly remained within the harbour feeding within 12 km of their colony; only two of the 22 birds tracked left the harbour reaching a maximum distance of 36 km from their colony. For Wellington penguins there was no difference in range, distance travelled or trip duration between incubation and chick rearing periods73. Of the three sites, those from Motuara Island showed the greatest variation between breeding stages and between individual birds. During incubation Motuara penguins foraged within 102±69 km of their colony (1 - 214 km) and their trips lasted 7±4 days (1-16 days). Three birds remained within 10 km of the colony; three undertook medium-distance trips 40–75 km from the colony into Cook Strait or the Marlborough Sounds, while eight crossed Cook Strait to feed 93–214 km north of the Island, some reaching the Taranaki Bight73. During chick rearing, Motuara penguins either made 1-day trips remaining 6-10 km of the Island or 2-day trips into Cook Strait reaching 36–43 km from the colony73. Buller birds also travelled further on longer duration trips during incubation (up to 5 days) than chick rearing (1 day), feeding west or north-west of their colonies. Wellington and Buller birds showed little year to year variation in areas used, unlike the Motuara penguins where there was marked variation between years73. This study suggested that penguins breeding far from a major river mouth travelled further to find food than those nesting close to a river mouth.
Previous studies at Motuara Island also showed this to be a poor site for little penguins, the birds there diving more often than little penguins from Oamaru (mean number of dives per trip: 1,165 versus 809), deeper (mean depth: 10.1 versus 6.0 m) and longer (mean dive duration: 29.5 versus 22.4 seconds)77, with lower body condition, and poorer breeding success (0.71 chicks/pair) than those at Oamaru (1.44 chicks/pair)61,62,64. Incubation spells, thus foraging trips, were about twice as long at Motuara than Oamaru61. On predator-free Motuara Island breeding failure was generally due to chick starvation or adult desertion, whereas at Oamaru, predation was the main mortality factor62,64. The guard stage was shorter at Motuara Island than at Oamaru, and chicks fledged at a lower body mass, again indicative of less favourable foraging conditions62.
A study comparing foraging ecology across the entire range of the little penguin showed that at sites with high fledgling success such as Oamaru and Penguin Island (Western Australia) the penguins made shallower dives with lower diving effort than at sites with lower fledgling success such as Motuara Island and Phillip Island (Victoria)76. They conclude that availability of seas <50 m deep close to the colony is one important factor influencing breeding success.
There is only fragmentary information on the movements of adult little penguins between breeding seasons in New Zealand with no information on dispersal of juveniles. Wellington little penguins appear to remain in the harbour year-round returning to their colony frequently, with only three of the 435 adult penguins banded on Matiu-Somes Island between 1954 and 1958 seen outside Wellington Harbour55,60.
Of 168 banded little penguins captured at Pilots Beach, Otago Peninsula between September 1999 and December 2000, nine were banded at Oamaru 80 km away, one at Penguin Beach 2 km away, the rest from Pilots Beach or adjacent Taiaroa Head51.
In both studies penguins were far more likely to be resighted at the point of banding where regular searches were made than elsewhere, thus movements away from their breeding colony will occur more often than suggested by these results.
Sharks are reputed to prey on little penguins and barracouta (Thyrsites atun) reputed to attack penguins but the numbers taken, if indeed sharks or barracouta are even implicated are unknown. Thousands of sharks caught in Australia whose stomach contents were inspected did not contain penguin remains (A. Chiaradia, pers. comm.)
There are two published records of New Zealand fur seals (Arctocephalus forsteri) attacking little penguins at sea78,79 with three records of predation by seals on the West Coast (Table 3). Penguin feathers have occasionally been found in fur seal scats.
On land, Weka are probably capable of taking penguin eggs and chicks but we know of no verified account of this happening.
In New Zealand the major land-based threats to little penguins appear to be loss or modification of breeding habitat through land-development or erosion, deaths due to dogs, road kill, introduced predators and disturbance by people. The relative intensity of these threats varies regionally.
Road kill poses a significant threat to little penguins wherever they nest near roads. This was the major land-based cause of death in the Buller Region until penguin-proof fences were built in those areas where most road- kills occurred to prevent the penguins straying onto the highway (http://www.bluepenguin.org.nz/pahautane-penguin-fence/). At the Oamaru Blue Penguin Colony, tunnels were installed under the access road to avoid road kills by tourist traffic.
Little penguins are long-lived and strongly philopatric thus, loss or modification of breeding habitat, even if no birds are killed, can have long-lasting effects on breeding productivity and inbreeding may be of concern in the small colonies that are now typical of some parts of New Zealand.
Changes in the density and composition of vegetation have been found to influence the breeding success of little penguins59. Fire is a risk in drier parts of their range such as Banks Peninsula and Chatham Islands8,9.
Trampling of burrows by cattle and sheep can occur where birds nest on farmland, or by feral goats or even deer elsewhere8,9, but trampling of burrows is probably rare. Possums and rabbits could potentially compete with penguins for burrows but there appear to be no verified records of this happening.
Disturbance by people is likely to be problematic at some well-known unprotected sites such as the Oamaru Creek colony and those in Wellington city.
Uncontrolled dogs are one of the major threats to little penguins9,78, the penguins being particularly vulnerable at night when moving between the sea and their burrows. Dogs are capable of digging penguins out from their burrows although we do not know of any verified reports of that. In February 2001, 116 penguins from the Oamaru Creek Colony were killed by two dogs over the course of just two nights (Mattern, pers. obs.). At Cape Foulwind on the West Coast, 15 adult little penguins were killed, probably by a single dog on a single night, and several small colonies at Punakaiki have been extirpated probably by dogs (West Coast Penguin Trust unpublished).
Predation by mustelids requires further research although the information available suggests that ferrets pose more of a threat than stoats. The most conclusive study of mustelid predation is that by Challies79 at Harris Bay, Banks Peninsula. Those colonies that were accessible to predators, remained stable during the 1970’s, but declined suddenly after 1981; two colonies were extirpated and 42 of the 47 penguins found dead had wounds typical of those inflicted by mustelids79. Of the 47 mustelids trapped between 1981 and 1995, 43 were ferrets, three were stoats and one a weasel (Mustela nivalis). Sixteen of the penguin kills could be attributed to ferrets but both ferrets and stoats were present when three other penguins were killed79. Predation affected the surviving birds indirectly by breaking pair bonds and skewing the sex ratio as females were killed more often than males79.
Penguins disappeared from most Banks Peninsula colonies accessible to predators during the 1980s and 1990s except in areas where feral cats were the dominant predators79,80. The declines in the 1980s coincided with an increase in ferret and rabbit numbers following changes in rabbit control during the 1970’s. No penguins were preyed upon between September and January when rabbits were most numerous; most penguins being taken in Autumn and Winter when mammal prey was scarce79. Ferret numbers on Banks Peninsula declined after 2000 following the introduction of rabbit haemorrhagic disease, allowing some recovery in the penguin population79.
Ferrets were the only species of mustelid known to prey on little penguins in the Oamaru area81 where in December 1999 they killed about a third of eggs and chicks but did not kill any adult penguins39.
On the West Coast breeding success and survival of eggs, chicks and adults were not significantly different in penguin colonies with, or with no predator control and mustelids appeared to constitute a very minor threat to little penguins (R. Lane and K-J. Wilson unpublished). At those West Coast colonies stoats were common, weasels rare but ferrets absent.
In Otago, most extant colonies are on islands or sites where predators were absent or were protected from predators by physical barriers or trapping56,78. Mustelids were the main predators recorded at Taiaroa Head, Otago Peninsula, although Norway rats (Rattus norvegicus) preyed on little penguin eggs during one season, even then in just one of the three sub-colonies studied56.
The impact of feral cats (Felis catus) on little penguins is uncertain. Taylor8 lists cats as predators of little penguins on Banks Peninsula citing an early report by Chris Challies, although in a recent paper Challies79 states that while penguin numbers declined in most colonies accessible to ferrets ‘the main exceptions being those in areas where feral cats remained the dominant predator’. Penguin feathers have been found in cat scats on the Chatham Islands9 and one probable instance of predation by a cat has been recorded on the West Coast (Table 3). Cats were a significant threat to little penguins in Tasmania5.
Feral pigs (Sus scrofa) can root out and kill little penguins9.
A review of the information available on parasites and diseases in New Zealand penguins is given by Duignan82. Pulmonary infection due to Aspergillosis has been recorded in emaciated beach-cast, juvenile little penguins. Fleas, ticks, mites and lice occur on most penguin species with three species of ticks Ixodes kohlsi, I. auritulus and I. eudyptidus recorded from little penguins. Endoparasitic cestodes, nematodes, trematodes, and acanthocephalans have been found in little penguins but neither these nor the ectoparasites appear to have much effect on the health of well-fed birds but can accentuate the impact of starvation82. High seroprevalence of avian malaria has been found in little penguins from Codfish Island/Whenua Hou; deaths due to avian malaria have not been reported from New Zealand but have occurred in Australia82.
With their wide latitudinal span from warm temperate Northland to cool Stewart Island, little penguins may at first glance appear sufficiently adaptable to cope with climate change, but such a complacent view is ill advised. A recent assessment of the impact climate change is likely to have on Australian birds showed seabirds to be particularly vulnerable83. While climate warming may directly contribute to the death of penguins through overheating, as has happened in Australia, it is the, associated changes such as ocean warming and increased storm frequency and intensity that are more likely to affect seabirds. Research on other species suggests that extreme climatic events are more likely to impact penguins than long-term averages84.
The seas surrounding New Zealand, the Tasman Sea and southern and eastern Australia comprise one of the world’s major marine biodiversity hotspots which, through climate change, is likely to experience reductions in primary productivity and trophic shifts85 that will affect seabirds including little penguins. A major concern is that an increase in intensity and frequency of sea surface temperature (SST) anomalies will affect breeding onset and trigger a mismatch between marine productivity and peak breeding85.
The ways in which various marine parameters affect little penguins and the responses of the birds to these have been subject to intensive research in Australia (for example see86–89. Research on how variations in marine parameters affect little penguins in New Zealand is much more limited.
At Oamaru, high marine productivity (estimated by chlorophyll-a) correlated positively with early breeding, higher breeding success and better survival of breeding penguins, the effect being most marked when chlorophyll-a was high in the months preceding the breeding season90. Breeding was delayed in years when seas were warmer38, so on that basis we might expect ocean warming to negatively affect breeding success. During prolonged periods of rough weather Oamaru penguin parents returned less frequently, increasing the likelihood of egg desertion when the foraging bird failed to return before the incubating bird’s reserves become exhausted, or chicks that were fed less frequently died or fledged at lower weights90. Wrecks, when large numbers of little penguins wash up dead on beaches, occur more often following prolonged bouts of stormy weather47,48, but may also be a result of low prey abundance or harmful algal blooms9. Wrecks appear to be a particular issue in Northland48.
Fisheries bycatch is a major threat to penguins worldwide with 14 of the 18 species recorded as bycatch, with set-nets and trawls posing the greatest threat to penguins with rare captures on longlines91.
In New Zealand, little penguins are caught and drowned in inshore set-nets, drag-nets and possibly also in trawl, purse-seine and long-line fisheries but the numbers killed and locations where kills occur are very poorly documented91. In 2016 eight Little penguins were caught in a single net set for butterfish (Odax pullus) in the Stewart−Snares area91. Little penguins are known to be caught in set nets around Motunau Island and drag-nets at Timaru6. The commercial fisheries most likely to cause penguin by-kill are small inshore vessels which are not required to carry observers and we suspect few penguins killed are reported. Penguins are less likely to be caught by larger vessels that use trawls or long-lines, the commercial fisheries where observer coverage is best. The extent of bycatch from recreational fishers is unknown.
There is little if any evidence to suggest over fishing has reduced prey abundance for penguins5,8. Little penguins have died on mass after a viral disease decimated their pilchard prey in both Australia and the North Island92,93.
Penguins are especially vulnerable to oil pollution with particular risk around major ports such as Whangerei, Auckland, Tauranga, Wellington and Lyttelton; all busy ports with little penguin colonies close by. Eighty-nine Little penguins were found dead and 383 live birds found contaminated with oil following the wreck of the container ship ‘Rena’ on Astrolabe Reef near Tauranga on 5 October 2011. An oil spill of this magnitude would have had an even greater impact on seabirds had it not been for the proximity of the wreck to a major city with all the infrastructure required to find, rescue and rehabilitate seabirds.
Little penguins breeding on Motuara Island foraged as far away as the Taranaki Bight during incubation73, the very place where Trans-Tasman Resources Limited (TTR) have a permit that allows them to extract iron ore from up to 50 million tonnes of sea-bottom sand each year (https://www.ttrl.co.nz/projects/south-taranaki-bight/). Ninety percent of the sand will be returned to the sea bed. Such at-sea sand mining is likely to increase turbidity and disrupt the food chain, but the impact of this and the continuous presence of a large 335 m long ore processing ship working in the area will have on penguins is unknown but potentially severe. Australian little penguins avoided turbid water when foraging even when those turbid waters had higher productivity than the preferred less turbid waters nearby94. They suggest that the visual hunting penguins are less successful in catching prey in turbid water. TTR have a prospecting permit for the South Island West Coast extending from Ross in the south, to north of Karamea, from one kilometre offshore out to the 12 nautical mile territorial limit (https://www.ttrl.co.nz/projects/westland-sands/), coinciding with areas where Buller little penguins forage73.
Plastic ingestion is a growing threat to most seabirds95 although penguins are perhaps less vulnerable that many other species. Chemical contaminants pose an ongoing but up to now minor threat to penguins in New Zealand. Organochlorines and heavy metals are found in Australian little penguins but whether these occur at detrimental levels was not determined5.
There are anecdotal reports of little penguins killed or injured by boat strike in the Hauraki Gulf and as the number of recreational boats is increasing this threat is likely to grow.
Much of the best research published on little penguins in New Zealand has been undertaken at Oamaru or Otago Peninsula where the penguins are potentially a different taxon than penguins elsewhere in New Zealand. This bias toward Otago based research is particularly marked for population trends, breeding biology, mate, nest site and colony fidelity, foods, foraging ecology, and weather/climate impacts on breeding; all aspects of biology critical to an understanding of conservation requirements. Regardless of taxonomy, due to regional differences in ecology and environment, New Zealand little penguins need to be managed at the population (or regional) level.
Clarify species status
In order to clarify the taxonomic standing of the two putative taxa use the Tobias criteria26 to compare the behavioural, biological and ecological differences between the New Zealand and the Australian/Otago taxa.
Determine when the taxa diverged from one another.
Gene flow analysis
Analyse large genomic datasets to test historical and/or contemporary gene flow between the two taxa.
In order to understand the population trends of New Zealand little penguins which, due to differing marine environments, food availability and threats, are likely to vary region to region it is necessary to monitor changes in population size and breeding success at different parts of New Zealand. With scientific guidance much of this could be done by community groups or volunteers.
While we know the overall distribution around New Zealand moderately well, there is robust data on little penguin distribution and abundance for just a few parts of the country. A colony database listing all known little penguin colonies together with estimates of numbers (where available) have been compiled by by K-J. Wilson in 201928
Conservation management requires an understanding of demography (in human terms births deaths and marriages) which in turn affects breeding success and population trends. Demography of little penguins has not been well researched in New Zealand, although analysis of Chris Challies long-term studies may provide much of the required data.
Distribution & abundace
Distribution and abundance of little penguins in selected areas throughout New Zealand, of particular concern is Northland where major wrecks have occurred and pressure from people and development is greatest.
Population trends on Chathaml Islands
To determine population trends and breeding success, annual monitoring at selected colonies at the Chatham Islands and for mainland and offshore island sites throughout New Zealand.
Demography & population dynamics
Population dynamics including data on age of first breeding, annual productivity, first year survival, and annual survival of adults; a comprehensive analysis of Chris Challies’ data set could provide much of the required data.
Development of monitoring protocols
Develop monitoring protocols suitable for use by researchers, community groups and individuals.
Stock-take of monitoring efforts
Compile a list of all little penguin colonies where annual monitoring is undertaken or where annual monitoring has occurred in the past.
Standardise monitoring pracices
Select those colonies in R.2.M5 where annual monitoring should be continued or resurrected and provide the support required to ensure annual monitoring in those selected colonies continues, preferably using standardised methodology.
Continue long-term monitoring programmes
Colonies where we know annual monitoring has/does occur are; Otago Peninsula, Oamaru, Flea Bay and Harris Bay (30 years) (Banks Peninsula), Motunau Island (30 years), Charleston (12 years) and Okarito (West Coast), Wellington city, Matiu/Somes Island (7 years) (Wellington), Mt Maunganui (Bay of Plenty). We recommend monitoring be continued at these sites.
Fill monitoring gaps
Identify and attempt to fill major geographical gaps in monitoring coverage. Gaps include; Chatham Islands, Stewart/Foveaux, Nelson/Marlborough, Hawkes Bay, Taranaki, Hauraki Gulf and Northland.
Estimate current population size in those areas, or for those colonies where population estimates were made >10 years ago using comparable methodology.
Facilitate data analysis & publication
Analyse and publish Chris Challies's long-term demographic study on Motunau Island and Harris Bay, Banks Peninsula. Similarly, analyse data from transponder trials on Somes Island (Mike Rumble).
Determine emigration rates and distance between natal and breeding colonies.
Little penguins obtain all their food at sea and spend most of their lives at sea, circumstantial evidence suggests that some of the declines in their numbers observed are the result of marine rather than terrestrial threats. Conservation management requires much more robust knowledge of their marine ecology than we have at present.
Little penguins experience regional differences in the marine environments thus the foods available to them. Further knowledge of regional and seasonal variation in diet could help explain differences in foraging effort, breeding success and the timing of egg laying.
Foraging ecology during breeding
Foraging range using GPS dive loggers during the breeding season at representative colonies throughout their New Zealand range. Ideally multi-year studies during all stages of the breeding cycle, but most crucial are those during chick rearing.
Satellite/GLS tracking of breeding penguins from representative colonies throughout their New Zealand range during the pre-moult period. If feasible fledglings, to find out where they go between moult and breeding.
Model climate effects
Climate change and sea surface warming will impact on Little penguins. Modelling may help predict and manage impacts.
Diet studies throughout their New Zealand range.
Collect blood and feathers for stable isotope studies.
Faecal prey DNA
Use non-invasive molecular methods to directly obtain data on diet using faecal samples
Breeding biology has been studied in detail in Australia and in moderate detail in New Zealand. The main gaps in our knowledge are around the timing of breeding and breeding success which appear to vary regionally. The influence of offshore marine conditions and climate on breeding success could provide useful insights into ways in which climate change is likely to affect the penguins in future.
Timing of breeding & reproductive success
Timing of the breeding cycle and breeding success of Little penguins at the Chatham Islands and at selected locations on mainland New Zealand in regions where no previous studies have been undertaken.
Climate effects on breeding success
For colonies experiencing different offshore marine conditions and climates, determine the way annual variation in prevailing environmental conditions affect timing of the breeding season and breeding success.
Obtain further data on nest site, mate and colony fidelity.
The research priorities above all contribute to our understanding of the ways different aspects of their ecology influence the threat status of little penguins in New Zealand. In this final section we list research topics that directly concern threats to the birds.
Introduced predator impacts
Determine the impact introduced predators have on little penguins. The impact appears to vary region by region.
Record the cause of death for penguins at monitored sites.
Study the cause of periodic die-offs of little penguins, the northern North Island being of particular concern.
Investigate boat impacts
Determine what role, if any, recreational and commercial vessels play in little penguin mortality in the Hauraki Gulf and other penguin foraging areas with high marine traffic.
Thanks to Dr Andre Chiaradia, Tess Cole, Dr Phillipa Agnew, Graeme Taylor and Dave Houston for their helpful comments on drafts of this report. They and Bruce McKinlay provided additional information and/or sent copies of reports and papers that contributed to this report. This review was funded by the T-Gear Charitable Trust and the Birds-New Zealand Research Fund. Thanks so much for supporting our work. We are especially grateful to Peter Gaze for his support and interest throughout.