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.
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.