BirdLife species factsheet for Newell’s Shearwater: http://datazone.birdlife.org/species/factsheet/newells-shearwater-puffinus-newelli
Follow a taxonomic reassessment, Newell’s Shearwater (Puffinus newelli), has been split into Newell’s Shearwater (P. newelli) and Rapa Shearwater (P. myrtae). The newly defined Newell’s Shearwater breeds on Hawaiian Islands, predominantly on Kaua`i, while Rapa Shearwater is only known to breed on four tiny islets around Rapa, French Polynesia, and also potentially in the interior of the main island too (see Thibault and Varney 1991, Shirihai et al. 2017, del Hoyo et al. 2018).
Both of the newly recognised taxa are under threat from introduced predators, with rats, cats and the mongoose Herpestes javanicus all potentially impacting P. newelli (NSWG 2005), while cats and Polynesian Rats (Rattus exulans) may be impacting P. myrtae (see Thibault and Varney 1991). Introduced species may also be impacting habitat quality for both species too, with habitat alteration by pigs, goats and strawberry guava on Hawaiian islands (Mitchell et al. 2005, NSWG 2005); while goat grazing may be having an impact on habitat quality for P. myrtae too, in addition to anthropogenic land clearance and cultivation (see Thibault and Varney 1991). It is also not only introduced species that have impacted P. newelli. Hurricanes Iwa and Iniki both had a devastating impact on forests of Kaua`i in 1982 and 1992 (e.g. Ainley et al. 1997); and the species is heavily impacted by collisions with man-made structures as well as being attracted by artificially lighting (see Podolsky et al. 1998, Mitchell et al. 2005, Anon. 2007).
The taxonomic concept of P. myrtae was recently assessed by UICN France et al. (2015), in the Red List of French Polynesia, to be Endangered (although in there it is treated as a subspecies of P. auricularis), yet this document does not provide supporting evidence for the criteria string used.
The pre-split species was listed as Endangered due to declines placed in the range 50-79% over three generations (BirdLife International 2018) as a result of the known threats to individuals from Hawaii (as the majority of the pre-split species was of subspecies P. n. newelli), but recent information from Raine et al. (2017) suggests that declines in the newly defined P. newelli could be occurring at an even greater rate.
Therefore, it appears that both species warrant a thorough assessment as it is likely that they both warrant listing under a threatened category. The assessments for both taxa are provided below.
P. newelli – Radar survey data has shown that, since Hurricane Iniki, the Kaua`i number of individuals may have declined by as much as 93.5% between 1993 and 2013, driven by key threats such as introduced predators, light attraction, collisions with powerlines and habitat alteration (Raine et al. 2017). It is considered that potentially 90% of the global population is from Kaua`i (see Griesemer and Holmes 2011), and so using the minimum population estimates from Joyce (2016), and assuming that trends for individuals breeding on other islands are stable, would give an ongoing population decline of >99% over three generations (46.5 years). It is uncertain whether the rate of decline has been consistently that high over the past three generations, though. Without targeted conservation work against the key threats to the species, it is plausible though that such declines may continue into the future. Therefore, it is proposed that the species would warrant listing as Critically Endangered under criteria A3bce+4bce.
P. myrtae – While the threats this species faces may be considered to be causing population declines, there is no clear evidence of the rate of decline. Therefore, the species cannot be accurately assessed against this criterion.
The Extent of Occurrence (EOO) for both of these species has not been calculated per IUCN guidelines yet (IUCN 2001, 2012). However, it is thought highly unlikely that either species would approach the threshold for Vulnerable under criterion B1.
P. newelli – While the Area of Occupancy (AOO) for this species has not been calculated per IUCN guidelines (IUCN 2001, 2012) after its split, the removal of the Rapa AOO from the pre-split AOO (710km2) is unlikely to push the AOO of the newly-defined P. newelli below the threshold for Endangered (500km2). The species is restricted to only a limited number of locations* (<10), and the population size and the area/quality of habitat are thought to be in continuing decline. Therefore, this species would warrant listing as Vulnerable under criterion B2ab(iii,v).
P. myrtae – The AOO of this species has not been calculated yet per IUCN guidelines (IUCN 2001, 2012), yet it is highly likely to be very small (at least <500km2). Thibault and Varney (1991) suggest that the species may be found on only 4 islets, as well as potentially on the main island of Rapa; and the key threat being from invasive predators, each of these localities may be considered a location*. As the threats the species faces are thought to be causing a decline in the population and area/quality of habitat for the species, then P. myrtae would warrant listing as Endangered under criterion B2ab(iii,v), as per UICN France et al. (2015).
P. newelli – The species is estimated to be in continuing decline. There have been several population size estimates for this species (see Griesemer and Holmes 2011), but the most recent gives a minimum population estimate of 27,011 individuals (Joyce 2016). This suggests that the population size would not meet the threshold for Vulnerable under this criterion (10,000 mature individuals). The species could, though, be precautionarily listed as Near Threatened under criterion C2a(ii), as the ranging movements of seabirds mean that the species should be considered to occur all in one subpopulation.
P. myrtae – In 1974 the population size was estimated at 265-380 pairs (excluding any potential birds breeding on the main Rapa Island), but no individuals were located during surveys in 1989 (Thibault and Varney 1991). A survey of Morotiri found no individuals of this taxon (Gaskin et al. 2006), and a visit to Rapa in 2017 found only a very small number of individuals (though this was likely not during the breeding season) (S. Cranwell per M. O’Brien in litt. 2018). At sea surveys find the occasional individual, but it appears highly unlikely that there 500-800 mature individuals remaining (M. O’Brien in litt. 2018). Further survey work during the breeding season is required to better quantify the population size, but it is tentatively proposed that it be placed in range 50-249 mature individuals, although it potentially could be lower than this.
Contra UICN France et al. (2015), the ranging behaviour of seabirds makes it unlikely that the species should be considered to be in more than one subpopulation (see IUCN 2001, 2012), and so, with the species considered to be undergoing a continuing decline, it would warrant listing as Critically Endangered under criterion C2a(ii).
P. newelli – The population size is too large to warrant listing under criterion D1. It does breed on only a limited number of islands in Hawaii, but the number of locations* where it is found is potentially still >5, and so it would warrant listing as Near Threatened under criterion D2.
P. myrtae – Its very small population size (suspected to be at least <250 mature individuals), means that the species would warrant listing as at least Endangered under criterion D.
The fact it is found at only a very limited number of locations, with sufficient threat to potentially drive the species to Critically Endangered or Extinct within a short period of time, means it would trigger a listing as Vulnerable under criterion D2.
Criterion E – To the best of our knowledge there have been no quantitative analyses of extinction risk carried out for either of these species. Therefore, they cannot be assessed against this criterion.
Thus, overall it is proposed that P. newelli be listed as Critically Endangered under criteria A3bce+4bce and P. myrtae as Critically Endangered under criterion C2a(ii). Comments are welcome on these proposed listings, but 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’ Red List status. Therefore, please make sure your comments are about the proposed listings.
*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).
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del Hoyo, J.. Collar, N.; Kirwan, G. M. 2018. Newell’s Shearwater (Puffinus newelli). In: del Hoyo, J., Elliott, A., Sargatal, J., Christie, D.A. & de Juana, E. (eds.). Handbook of the Birds of the World Alive. Lynx Edicions, Barcelona. (retrieved from https://www.hbw.com/node/467278 on 12 April 2018).
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