South Georgia Diving-petrel (Pelecanoides georgicus) is being split: assessment of newly recognised taxa.

BirdLife species factsheet for South Georgia Diving-petrel

Following a taxonomic reassessment, South Georgia Diving-petrel (Pelecanoides georgicus) is being split into South Georgia Diving-petrel (P. georgicus) and Whenua Hou Diving-petrel (P. whenuahouensis).

The newly-defined South Georgia Diving-petrel occurs in the southern Atlantic, Indian and Pacific Oceans, with remaining colonies in South Georgia (Georgias del Sur) in the south Atlantic, on the Prince Edward Islands (South Africa), Crozet and Kerguelen Islands (French Overseas Territories) and Heard Island (Australia) in the southern Indian Ocean and on Macquarie Island (Australia) and nearby Bishop Islet (Australia; Fischer et al. 2018a). The pre-split species was listed as Least Concern, with a global population estimated to number around 15,000,000 individuals (Brooke 2004) and suspected to be in decline owing to predation by invasive species (de Hoyo et al. 1992), and other ongoing threats. Following the split of the Whenua Hou Diving-petrel, the newly-defined South Georgia Diving-petrel is still likely to number in the millions (Fischer et al. 2018a), has a large range and is unlikely to be declining at a rate approaching the threshold for listing as threatened under Criterion A. Therefore, unless new information becomes available, South Georgia Diving-petrel will be retained as Least Concern.

The newly-split Whenua Hou Diving-petrel breeds only in the dunes of one bay of Codfish Island/Whenua Hou (New Zealand), where it has a very small population and may be declining (Fischer et al. 2018a). We are therefore undertaking a full assessment of the species’s Red List Category. Our current information on the species’s conservation status will now be compared to all Red List Criteria.

Criterion A – P. whenuahouensis underwent a historic decline, likely due to invasive species. Introduced predators were subsequently removed from Codfish Island and the population of P. whenuahouensis underwent an increase from 30-40 pairs in 1978-1991 (West and Imber 1989) to 100-200 individuals in 2000 (Taylor 2000). In 2013 however, the population size was considered to be lower than 150 individuals (Taylor 2013). Overall, the species has not been undergoing an overall reduction in population size over the past three generations (34.2 years).

The species breeds in dunes and the area and quality of its habitat are thought to be declining due to encroachment of forest and the spread of invasive plant species (Taylor 2013). The species’s habitat is also at risk from storm damage: In 2003, a storm extirpated at least 15% of the population, destroyed 40% of the nests, and removed the first 10m of the dunes (Cole 2004). The intensity of storms may increase due to climate change, leading to further future habitat damage and associated population declines (Fischer et al. 2018b). Although the species’s population is suspected to undergo a decline over the next three generations due to a reduction in the area and quality of habitat, we do not currently have information to suggest that the rate of reduction will approach 30% over three generations. The species is therefore assessed as Least Concern under Criterion A.

Criterion B – The species’s offshore distribution is not well-known, but the species has a highly restricted breeding colony, estimated to occupy just 0.018 km2 (Fischer et al. 2018b). To assess a species under Criterion B2, the Area of Occupancy (AOO) should be calculated at the scale of 2 km by 2 km grid squares. By overlaying 2 km by 2 km grid squares over the species’s mapped breeding colony, the AOO is estimated at 4-8 km2, thereby meeting the threshold for Critically Endangered under Criterion B2. However, to list the species as threatened under Criterion B, two of conditions a-c must also be met.

The species is not severely fragmented since it breeds at just one site. The number of locations* is determined by the area of impact of the most serious plausible threat. If the most serious plausible threat is considered to be storms, the species may be considered to have 2-5 locations (based on the area of impact of the storm in 2003), which would meet condition a at the level of Endangered. If the most serious plausible threat is considered to be the introduction of invasive predators, then the species may be considered to have a single location, meeting condition a at the level of Critically Endangered. It is unclear whether the species’ population size is currently declining, but the species’s area and quality of habitat is considered to be declining as a result of encroachment of forest and invasive plant species (Taylor 2013). Condition b is therefore likely to be met. There is no evidence that the species’s population or range size are undergoing extreme fluctuations. Condition c is not met.

The species’s AOO falls beneath the thresholds for listing the species as Critically Endangered and condition c is met. Condition b is also met at the level of Endangered or Critically Endangered, depending on the number of locations. The species may therefore qualify for listing as Endangered or Critically Endangered under Criterion B2ab.

Criterion C – The species’s population size has been estimated at fewer than 150 individuals (Taylor 2013), which roughly equates to 100 mature individuals. The population size meets the threshold for listing as Critically Endangered under Criterion C.

We do not currently have information to indicate an ongoing decline in mature individuals. However, the species’s habitat is considered to be shrinking as a result of encroachment of forest and invasive plants (Taylor 2013) and the species may be at increasing threat from storms as a result of climate change (Fischer et al. 2018b). The species may therefore be inferred to be undergoing a continuing decline. We do not have direct data from which to estimate a project the rate of continuing decline, so the species does not qualify as threatened under Criteria C1. The species has a single subpopulation with fewer than 150 mature individuals, and thus meets Criterion C2a(i) at the level of Endangered, but not at the level of Critically Endangered. All individuals are thought to be in one subpopulation, meeting Criterion C2a(ii). The species therefore qualifies for listing as Critically Endangered under Criterion C2a(ii).

Criterion D – The species’s population size has been estimated at fewer than 150 individuals (Taylor 2013), which roughly equates to 100 mature individuals. This meets the threshold for Endangered under Criterion D.

Criterion E – To the best of our knowledge no quantitative assessment of the probability of extinction has been conducted for this species, and so it cannot be assessed against this criterion.

Based on the above assessment, it is proposed to list Whenua Hou Diving-petrel (Pelecanoides whenuahouensis) as Critically Endangered under Criterion C2a(ii), and possibly also under Criterion B2ab. To allow us to achieve a clearer assessment of the species’s status, information is requested on the species’ population trends and the threats impacting on the species, both currently and in the near future.

Please note that this topic is not designed to be a general discussion about the ecology of the species, rather a discussion of the species’s Red List status. Therefore, please make sure your comments are about the proposed listing.

*The term ‘location’ refers to a distinct area in which a single threatening event can rapidly affect all individuals of the taxon present, with the size of the location depending on the area covered by the threatening event. Where a taxon is affected by more than one threatening event, location should be defined by considering the most serious plausible threat (IUCN 2001, 2012).

An information booklet on the Red List Categories and Criteria can be downloaded here and the Red List Criteria Summary Sheet can be downloaded here. Detailed guidance on IUCN Red List terms and definitions and the application of the Red List Categories and Criteria can be downloaded here.

References

Brooke, M. (2004) Albatrosses and petrels across the world. Oxford University Press.

Cole, R. (2004) Summary of South Georgian Diving Petrel field observations for 2003/04, Codfish Island/Whenua Hou. Invercargill, New Zealand: Department of Conservation, Southland Conservancy.

del Hoyo, J., Elliot, A. and Sargatal, J. (1992) Handbook of the Birds of the World, Vol. 1: Ostrich to Ducks. Lynx Edicions, Barcelona, Spain.

Fischer, J. H., Debski, I., Miskelly, C. M., Bost, C. A., Fromant, A., Tennyson, A. J., Tessler, J., Cole, R., Hiscock, J. H., Taylor, G. A. and Wittmer, H. U. (2018) Analyses of phenotypic differentiations among South Georgian Diving Petrel (Pelecanoides georgicus) populations reveal an undescribed and highly endangered species from New Zealand. PloS One: 13(6), p.e0197766.

Fischer, J. H., Debski, I., Taylor, G. A. and Wittmer, H. U. (2018) Nest site selection of South Georgia Diving-petrels Pelecanoides georgicus on Codfish Island, New Zealand: implications for conservation management. Bird Conservation International 28(2): 216-227.

Taylor, G.A. 2013. South Georgian diving petrel. In Miskelly, C.M. (ed.) New Zealand Birds Online. www.nzbirdsonline.org.nz West, J. & Imber, M. J. 1989. Surveys of South Georgian diving petrels (Pelecanoides georgicus) on Codfish Island. Notornis 36: 157-158.

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6 Responses to South Georgia Diving-petrel (Pelecanoides georgicus) is being split: assessment of newly recognised taxa.

  1. Johannes Fischer says:

    Criterion A
    Recent analyses of burrow counts at Codfish Island/Whenua Hou provided estimates of P. whenuahouensis population size and trend (Fischer et al. in press.). Specifically, the population size of P. whenuahouensis was estimated at 80 (95% credible interval = 72-92) mature individuals in 1978 and at 200 (95% credible intervals = 194-208) mature individuals in 2018. The population trend of P. whenuahouensis was estimated at λ = 1.023 (0.959-1.088) before the eradication of invasive predators (1978-1985). The population trend of P. whenuahouensis was estimated at λ = 1.017 (1.006-1.029) after the eradication of invasive predators (2002-2018). While P. whenuahouensis is likely to suffer from future declines under the increasing pressure of storms and storm surges, the species is not currently in decline. The species should therefore be assessed as Least Concern under Criterion A.

    Criterion B.
    On a 2 km by 2 km grid, the AOO of P. whenuahouensis is estimated at 4-8 km2, thereby meeting the threshold for Critically Endangered under Criterion B2. However, the most serious threat is perceived to be storms and storm surges, and thus the species may be considered to have 2-3 locations (not 2-5, as the storm in 2003 seriously degraded the breeding habitat rendering P. whenuahouensis considerably more vulnerable than pre-2003). Consequently, the species qualifies for listing as Endangered under Criterion B2ab.

    Criterion C.
    Recent analyses of burrow counts at Codfish Island/Whenua Hou estimated the population size of P. whenuahouensis at 200 (95% credible intervals = 194-208) adults in 2018. While the population is not currently declining, all mature individuals are restricted to a single population. As such, P. whenuahouensis qualifies for listing as Critically Endangered under Criterion C2a(ii).

    Criterion D.
    The population size of P. whenuahouensis has been assessed at 200 (95% credible intervals = 194-208) adults in 2018 (Fischer et al. in press.). This meets the threshold for Endangered under Criterion D.

    Criterion E.
    No quantitative assessments of probability of extinction of P. whenuahouensis have been conducted to date.

    Consequently, the Whenua Hou Diving-petrel (Pelecanoides whenuahouensis) should be listed as Critically Endangered under Criterion C2a(ii)

    References
    Fischer JH, Taylor GA, Cole R, Debski I, Armstrong DP & Wittmer HU. (in press.). Population growth estimates of a threatened seabird indicate necessity for additional management following invasive predator eradications. Animal Conservation XX: XXX-XXX.

  2. Paul Scofield says:

    Unfortunately the analysis and description of P. whenuahouensis by Fischer et al 2019 appears to have misinterpreted some important information that makes recognition of this taxon as a species untenable. Specifically:

    1) Genetic data published in Tizard et al 2019 and available here https://www.researchgate.net/publication/331029502_DNA_barcoding_a_unique_avifauna_An_important_tool_for_evolution_systematics_and_conservation and on Genbank make it clear that indeed the birds present on Codfish Island are not P. georgicus but that they are very closely related to P. exsul from Heard Island.

    2) The author’s incorrectly ascribe the heavy billed Diving-petrels with a white scapula on Heard Island and Kerguelen to P. georgicus. The syntypes of P. exsul were collected from the Kerguelen Islands by the Challenger and have the exact morphology interpreted (incorrectly) by Fischer et al 2019 as representing P. georgicus.

    3) Murphy & Harper 1921 discussed this issue comprehensively and recognised (correctly in my opinion) P. exsul as a full species based on both a morphometric and plumage characters and on the fact that they breed in sympatry on several island groups (including on the Auckland Islands).

    4) Fischer et al. 2017 misinterpreted the extinct populations on Enderby Island in the Auckland Islands as being (presumably) their new taxon when they were actually recognised as P. exsul as early at 1921.

    5) Representative of true South Georgian Diving-petrels P. georgicus are as range restricted as P. exsul being restricted to a very specific habitat (soft substrates at high altitude on high-latitude sub-Antarctic islands). South Georgian Diving-petrel occurs, for certain, only on South Georgia and the Prince Edward Islands. With data to hand I am unable to determine the species status of populations on Crozet and Bishop Islet off Macquarie Island.

    6) P. exsul occurs for certain currently on Heard Island, islands off Kerguelen Island, and Codfish Island (as confirmed by DNA). It would appear it was formerly on Enderby Island in the Auckland Islands and on Stewart Island. It may also be the taxon on Crozet and Bishop Islet off Macquarie Island. From the literature I was unable to determine if there are any Diving-petrels breeding on the alpine plateau of Macquarie Island but their species status would warrant further study.

    Thus the question for the Birdlife Committee in my opinion is firstly not what is the status of the dune nesting Pelecanoides on Codfish Island but on which islands does P. exsul occur and on which islands does P. georgicus. A corollary to this maybe does the New Zealand taxa warrant recognition as a subspecies.

    Fischer, J. H., Hjorsvarsdottir, F. O., Hiscock, J. A., Debski, I. G. O. R., Taylor, G. A., & Wittmer, H. U. (2017). Confirmation of the extinction of the South Georgian diving petrels (Pelecanoides georgicus) on Enderby Island. Notornis, 64, 48-51.

    Murphy, R.C.; Harper, F. 1921. A review of the Diving Petrels. Bull. Amer. Mus. Nat. Hist. 44: 495-554.

  3. Johannes Fischer says:

    I appreciate Paul’s concerns on the validity of P. whenuahouensis. However, there are several issues with Paul’s comments, including misinterpretation of various published articles on diving petrel identification and distribution. Consequently, Paul’s conclusions on distribution and status of P. georgicus, P. urinatrix exsul, and therefore P. whenuahouensis, appear inaccurate and non-parsimonious. Yet, I would like to point out that this forum is intended to discuss the threat status of P. whenuahouensis only, as stated above. As such I suggest that we leave the decision on the validity of this taxon to the BirdLife International taxonomic committee.

  4. Hannah Wheatley (BirdLife) says:

    Thank you very much for the helpful comments.

    Given that the data for P. whenuahouensis shows a positive population trend, we would now assess the species as not having a continuing decline, meaning that it would not be assessed as threatened under Criteria B or C. However, the population size estimate of 200 mature individuals qualifies the species for listing as Endangered under Criterion D.

    Therefore, our preliminary proposal for the 2019 Red List is to list Whenua Hou Diving-petrel (Pelecanoides georgicus) as Endangered under Criterion D.

    Please note that we will then only post final recommended categorisations on forum discussions where these differ from the initial proposal.

    The final 2019 Red List categories will be published on the BirdLife and IUCN websites in December, following further checking of information relevant to the assessments by both BirdLife and IUCN.

  5. Graeme Taylor says:

    The proposal to list this species as Endangered rather than Critically Endangered does not take in account the extremely narrow habitat range occupied by this species. Criteria B above lists the area of occupancy as 4-8 km2 (=400-800 ha) on an island (Whenua Hou or Codfish Island) that is 1400 ha in total size. It is immediately apparent to anyone who looks at a satellite view of the island (Google Earth for example) that the sand dune habitat used exclusively by this species for breeding does not cover a third to half of the island area. The beach at Sealers Bay is just 1km long(1000 m). The birds breed exclusively in the front dune system behind the mean spring high water tide zone, an area extending no more than 20m back from the beach tide line. Therefore the area they occupy is 20,000 m2 or just 2 ha (about 4 football fields). Behind the dunes is a shrubland community that this species has never been observed in and is regenerating into a taller forest habitat. The storm surges observed since 2003 (almost annually now) have carved off a strip of dunes at least 10m wide along the Sealers Bay dune removing breeding habitat and killing birds (corpses found on the beach after some storms). The species is being squeezed by climate change with forest growth accelerating in the back dunes as air temperatures warm and storms cutting away the front dunes as sea levels expand.

    On top of this issue is the serious and proven risk of pest mammal incursions. Fishing boats regularly anchor just offshore and on at least two occasions Norway rats (R.norvegicus) have been trapped in the dune systems as single island invaders. On two separate islands further north in NZ (Mana and Portland), a single incursion of a Norway rat halved the resident NZ shore plover population within 6 months until the pest was identified and removed by trapping and poisoning. On another small island that I monitor seabird populations, common diving petrel adults and chicks were almost entirely wiped out in several seasons by single incursions of Norway rats in one year and ship rats in another. A stoat incursion resulted in 70 dead diving petrels being found in one stoat den. Therefore in an area of occupancy of just 2 ha, there is a serious risk that a single rat coming off a boat could reduce the Whenua Hou diving petrel population substantially within a few months of arriving undetected. If this type of risky situation for a single island endemic does not meet Critically Endangered status I can’t see the point of having a red list.

  6. Hannah Wheatley (BirdLife) says:

    Recommended categorisation to be put forward to IUCN

    Thank you very much for the helpful comments in response to this proposal. Following further review, the recommended categorisation for this species has been changed.

    It should be noted that IUCN require us to calculate Area of Occupancy (AOO) as the total area of 2km x 2km grid cells that intersect a species’s occupied range (or for colonial breeders, breeding colonies). This is to standardise measurements of occupied range made at different levels of resolution and allow them to be compared against the same thresholds under Criterion B2. According to the IUCN Red List Guidelines (link at the end of the topic), ‘The need to scale estimates of AOO consistently follows logically from the adoption of fixed AOO thresholds in the Red List criteria and the sensitivity of AOO estimates to measurement scale. “The finer the scale at which the distributions or habitats of taxa are mapped, the smaller the area will be that they are found to occupy, and the less likely it will be that range estimates … exceed the thresholds specified in the criteria.”(IUCN 2001, 2012b).’ Thus, although we have calculated this species’s AOO as 4-8 km2, this does not imply that the area of the species’s breeding colony covers 4-8 km2; merely that it overlaps 1-2 4km2 squares placed over the map. Regardless, the AOO meets the threshold for Critically Endangered under Criterion B2.

    Although burrow counts have indicated that the population size is not currently declining, based on the additional information received, we can take a precautionary approach and assume that the quality of habitat is declining, and that this may negatively impact the species’s population size in the future. Thus, we can say that there is a continuing decline in ‘area, extent and/or quality of habitat’ and condition b under Criterion B is met.

    Taking into account the additional information provided about the risk of mammal introductions and their severe impacts on other species, it appears plausible that the introduction of rats onto Whenua Hou could destroy the whole colony within a short period of time, and hence we can state that the species has only a single location. Therefore, condition a would also be met at the level of Critically Endangered.

    Whenua Hou Diving-petrel (Pelecanoides whenuahouensis) is now recommended to be listed as Critically Endangered under Criterion B2ab(iii).

    The final 2019 Red List categories will be published on the BirdLife and IUCN websites in December, following further checking of information relevant to the assessments by both BirdLife and IUCN.

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