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. https://acap.aq/en/acap-species/316-westland-petrel/file
Best, H. A.; Owen, K. L. 1976. Distribution of breeding sites of the Westland Black Petrel Procellaria westlandica. Notornis 23: 233-242.
BirdLife International. 2017. Species factsheet: Procellaria westlandica. Downloaded from http://www.birdlife.org 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 http://www.iucnredlist.org/documents/RedListGuidelines.pdf
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.