Archived 2017 topics: Westland Petrel (Procellaria westlandica): request for information.

Westland Petrel, Procellaria westlandica, is known only to breed in the densely forested coastal foothills of Punakaiki, South Island, New Zealand (Best and Owen 1976, ACAP 2012). The most recent estimate of population size is 2,954-5,137 annual breeding pairs (Wood and Otley 2013), but given that not all individuals breed each year this is likely to be an underestimate for the number of mature individuals. Assuming that 25% of breeding age birds may skip breeding in any one year (as derived from long-term data sets on similar species) (B. Baker in litt. 2012), there could be 7,877-13,698 mature individuals. This is likely to be an increase since the 1970s, and the population continues to grow slowly (Waugh et al. 2015a).

The species is currently listed as Vulnerable under criterion D2 on the basis of it being restricted to only one very small area when breeding, which may make it susceptible to threats (see BirdLife International 2017). Following Tropical Storm Ita in 2014, there was considerable damage to the breeding area, with the loss or damage of up to 50% of the major colonies, which contain up to 75% of the breeding population (Waugh et al. 2015b). Fortunately, the storm occurred before the laying period and so adults may not have been killed in their nests, unless they were visiting prior to breeding (which some birds have been reported to do) (S. Waugh in litt. 2016), and some birds have moved between impacted colonies (S. Waugh in litt. 2016). Therefore, the level of destruction may not equate to any decline in population, and no population data subsequent to the storm are yet available, though surveys are currently underway (S. Waugh in litt. 2016).

It has been suggested that because of the impact of this Tropical Storm the species would warrant uplisting under criteria B1+B2. However, this does not appear to fit with IUCN guidelines (IUCN Standards and Petitions Subcommittee 2016). For a species to be listed under these criteria there must be evidence for a continuing decline in any of the following: i) the extent of occurrence, ii) area of occupancy, iii) area, extent and/or quality of habitat, iv) number of locations/subpopulations, or v) population size. While there has been a reduction in the area, extent and/or quality of habitat this has not been part of a continuing decline, instead being a one-off reduction. Therefore on current evidence this species does not meet the conditions required for uplisting under this criterion, following IUCN guidelines.

We acknowledge that the damage caused by this Topical Storm is concerning, and we request any more up to date information regarding the impact on the population following this event which could lead to a reassessment of its status.



ACAP. 2012. Westland Petrel Procellaria westlandica factsheet.

Best, H. A.; Owen, K. L. 1976. Distribution of breeding sites of the Westland Black Petrel Procellaria westlandicaNotornis 23: 233-242.

BirdLife International. 2017. Species factsheet: Procellaria westlandica. Downloaded from on 12/04/2017.

IUCN Standards and Petitions Subcommittee. 2016. Guidelines for Using the IUCN Red List Categories and Criteria. Version 12. Prepared by the Standards and Petitions Subcommittee. Downloadable from

Waugh, S. M.; Barbraud, C.; Adams, L.; Freeman, A. N. D.; Wilson, K.-J.; Wood, G.; Landers, T. J.; Baker, G. B. 2015a. Modelling the demography and population dynamics of a subtropical seabird, and the influence of environmental factors. Condor 117: 147-164.

Waugh, S. M.; Poupart, T.; Wilson, K-J. 2015b. Storm damage to Westland petrel colonies in 2014 from cyclone Ita. Notornis 62: 165-168.

Wood, G.; Otley, H. 2013. An assessment of the breeding range, colony sizes and population of the Westland petrel (Procellaria westlandica). New Zealand Journal of Zoology 40: 186-195.

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3 Responses to Archived 2017 topics: Westland Petrel (Procellaria westlandica): request for information.

  1. Susan Waugh says:

    Hi we have a ms that sets out some detailed information to add to the assessment review. We can send you that by email, please let me know the address.

    This is the relevant paragraph from the ms.
    “Based on our assessment of a revised area of occupancy (0.16 km2) and significant degradation to the habitat which is ongoing, we submit that a revision of the threat status from Vulnerable to Endangered is warranted (IUCN 2012). This assessment is on the basis of criterion B (less than 500 km2 of occupied area); with two criteria met: B2a (fragmented occupancy, with 20 or more colonies totalling 0.16 km2 within the single site), and 2biii (ongoing decline of habitat quality due to erosion at the slips and windfall sites documented following the 2014 storm).

    Regarding your comments about the size of the adult population; “Assuming that 25% of breeding age birds may skip breeding in any one year (as derived from long-term data sets on similar species) (B. Baker in litt. 2012), there could be 7,877-13,698 mature individuals. This is likely to be an increase since the 1970s, and the population continues to grow slowly (Waugh et al. 2015a).”
    There are no reliable counts of Westland petrels from before the Baker surveys (2006 – 2011), and these are the only quantitative, repeatable surveys to draw any information from. So there is an ‘n’ of 1 from which to make population trend assessments. Until there is a 2nd set of similar, quantitative surveys, you cannot state that the population has increased.

    Further, it’s not viable to extrapolate the findings of our one study colony across the entire population, and we make this point at various times in the 2015 demographic paper. This is because all the other colonies are small (eg <200 burrows) while the study colony is much larger (around 1000 burrows). They are subject to different pressures, and don’t respond the same to threats. We have been trying for the last few years to get good quality demographic data from a smaller colony nearby, but sadly 2/3 of its nests disappeared down the hill in a mudslide in 2014. So that no longer has a viable number of nests that exist from which to estimate survivorship, or even breeding success.
    Conclusion – there is no basis for stating there has been an increase since the 1970s, and the study colony we use for demographic analysis is not representative of the whole population.

    I don't believe that there is any information to state that the population has not suffered from the massive reduction in habitat it experienced in 2014, and while we hope that birds may redig burrows in new areas or remaining colonies, we haven't yet seen evidence of this. We recaptured one bird banded at a storm impacted colony at a nearby colony since the 2014 storm, but that's probably not a sound basis for stating that the population recover is underway. I would rather wait for evidence to make that claim.

    We submit that the reduction in habitat quality is ongoing, as the slips and windfall removed a lot of land, but there is continuing erosion of burrowed areas at the edges of these slips, which is still eating into colony area. The land is very steep, the canopy tree cover has largely been removed from the colony areas we are able to visit, exposing the remaining colony space to erosion from wind and rain. Its still very much an active situation.

  2. James Westrip (BirdLife) says:

    The New Zealand national status of this species has recently been re-assessed in the Conservation Status of New Zealand birds, 2016 (Robertson et al. 2017). There are differences in the Categories, Criteria and Thresholds for listing between Robertson et al. (2017) and those used when conducting IUCN Red List assessments, but in Robertson et al. (2017) Westland Petrel was listed as Naturally Uncommon. This means the species was assessed to be confined to a small geographic area, or small scattered populations, where this distribution is not a result of anthropogenic factors; it was also noted as being stable.

    Robertson, H. A.; Baird, K.; Dowding, J. E.; Elliott, G. P.; Hitchmough, R. A.; Miskelly, C. M.; McArthur, N.; O’Donnell, C. F. J.; Sagar, P. M.; Scofield, R. P.; Taylor, G. A. 2017. Conservation status of New Zealand birds, 2016. New Zealand Threat Classification Series 19. Department of Conservation, Wellington.

  3. Hannah Wheatley (BirdLife) says:

    Preliminary proposals

    Based on available information, our preliminary proposal for the 2017 Red List would be to list Procellaria westlandica as EN under criterion B2ab.

    There is now a period for further comments until the final deadline of 4 August, after which the recommended categorisations will be put forward to IUCN.

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

Comments are closed.