Justification of Red List category
This species qualifies as Endangered because it is restricted to one very small area when breeding, and its habitat is declining in quality due to erosion and landslips.
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), the population size is estimated at 7,877-13,698 mature individuals, rounded here to 7,900-13,700 mature individuals.
Following the 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).
The population was estimated to slowly increase at a rate of 1.8% per year between 1970 and 2012 (Waugh et al. 2015a). However, earlier counts are considered unreliable (S. Waugh in litt. 2017) so the population trend is uncertain.
Procellaria westlandica breeds in the densely forested coastal foothills near Punakaiki, South Island, New Zealand (Best and Owen 1976). It migrates in summer to central Pacific and eastern New Zealand waters, the east coast of Australia and off South America (Marchant and Higgins 1990, Brinkley et al. 2000), and is regularly recorded off the coast of Chile extending into the South Atlantic to the east of Tierra del Fuego (Spear et al. 2005). A large number were recorded in the area of the Golfo de Penas (400 individuals) and Canal Messier (850 individuals), Aisen (Chile), and all in heavy primary moult (Fraser 2009), potentially representing 10% of the world population of this species (Fraser 2009).
Behaviour The species is a colonial, winter breeder. Most eggs are laid in late May, and hatch mostly in mid to late July. Chicks fledge from November to December (ACAP 2012). In any given year, a large proportion of the population skip breeding; however, there is no discernible pattern to this behaviour, although it maybe linked to El Niño events (Waugh et al. 2006). Skipped breeders have lower survival rates, possibly owing to differences in the 'fitness' of individuals. Juveniles return to the colony as young as three years, but the age of first breeding is 7.5 years (Waugh et al. 2015a). During incubation and chick-rearing, satellite-tracking data indicate foraging principally on the continental slope off the West Coast of South Island, but birds regularly visit Cook Strait, the Chatham Rise and Fiordland, and frequently forage in the mid-Tasman sea (Freeman et al. 1997, 2001). Habitat Breeding They nest on densely forested hills at 20-250 m. Burrows are usually concentrated in areas where the ground is relatively open, and where take-off areas are close by. This is one of the few remaining petrels still nesting on mainland New Zealand, possibly due to more aggressively resisting attacks from land-based predators (Brooks 2011). Diet Fisheries waste is an important dietary component, perhaps forming more than half of solid food fed to chicks during the hoki fishing season (Freeman 1998). Subsequent satellite tracking studies have suggested that dietary analysis over-estimates the amount of food scavenged from trawlers and that the species continues to forage over wider areas than those occupied by the hoki fishery. Even individuals known to forage at fishing fleets acquire a large proportion of their food elsewhere (Freeman et al. 2001, Freeman and Wilson 2002).
The Westland Petrel is at risk from introduced species. A population of feral pigs has established within 20km of the breeding colonies, leading to concerns that, if the pigs discover the colonies, they will predate adults and cause habitat degradation, an issue that is exacerbated by their difficulty of eradication (Waugh and Wilson 2017). Feral dogs are present at locations very close to the breeding colonies, and vagrant dogs have killed petrels at the colonies previously (Waugh and Wilson 2017). Other predatory introduced mammals sighted in and around the colonies during 2010-2016 include Brushtail Possums, stoats Mustela ermine and rats Rattus spp. Nevertheless, productivity is relatively high, with around 65% of eggs laid fledging chicks (Waugh et al. 2015, Waugh and Wilson 2017), suggesting that their presence may not hinder breeding success. Cats Felis catus are considered a more significant threat and most chick deaths recorded in the 1990s were attributed to cat predation (Wilson 2016), however the levels of predation appear low and do appear to be causing a population decline.
Habitat loss and degradation is also a threat. In the past, farming may have destroyed some habitat, but presently the colonies are situated on land that is too steep and difficult to access for agriculture. In 2014 tropical storm Ita destroyed or damaged up to half of the area of assessed colonies, which contained up to 75% of the breeding population (Waugh et al. 2015). Severe erosion following the storm continues to cause the loss of burrows (Waugh and Wilson 2017).
At sea these petrels overlap considerably with fisheries (Waugh et al. 2018) and their ecological niche widens in El Niño years, indicating that food type is affected by climatic variation (Waugh et al. 2018). Non-breeders, which spend considerable time off South America, demonstrated reduced survivorship compared to breeding individuals. This is thought to be due to the effects of bycatch, both commercial and subsistence. The behaviourally (and visually) similar Black Petrel is killed as bycatch in artisanal fisheries off Ecuador and Peru (Mangel 2012) indicating that small-scale fisheries may be a significant source of mortality. Bycatch also occurs within the foraging range of breeding birds, and the species is considered at high risk of adverse population effects here also (Richard and Abraham 2015).Human exploitation is likely to occur, with equipment used to extract chicks from burrows found in 2011, but any take is considered likely to be very limited (Waugh and Wilson 2017). The 'fallout', attraction of petrels (especially fledglings) to lights at night, may be an important threat for the species, as it causes mortality through direct collisions and grounding, although the level of mortality is unknown (Waugh and Wilson 2017).
Conservation Actions Underway
CMS Appendix II and ACAP Annex 1. The breeding site is within the Paparoa National Park. The breeding colonies were designated as Westland Petrel Special Area in 1999, which restricts public access. A long-term study has been in place since 1969, covering social organisation, behaviour, breeding biology and aspects of population dynamics. A demographic study was undertaken between 1995 and 2003 (Waugh et al. 2006). Monitoring is being undertaken to check for the presence of pigs and dogs in the petrel habitat (S. Freeman pers. comm. per Waugh and Wilson 2017). Work is ongoing to raise awareness of the risks of lights and power line strikes among local residents so that downed petrels may be recovered and released (Waugh and Wilson 2017).
50 cm. Large, black petrel. Undersides of primaries may appear silvery. Yellowish bill, whiter in juveniles, has black tip. Black legs, feet. Similar spp. Larger than southern hemisphere shearwaters. Black Petrel P. parkinsoni becomes browner as ages, is smaller, especially bill. Differs from White-chinned Petrel P. aequinoctialis in black-tipped bill, absence of white chin (sometimes almost absent in P. aequinoctialis). Voice Staccato, wheezy, moaning notes at colony.
Text account compilers
Stuart, A., Sullivan, B., Taylor, J., Wheatley, H., Calvert, R., Black, A., Fjagesund, T., Hermes, C., Anderson, O., Martin, R., McClellan, R., Stattersfield, A.
Tennyson, A., Wilson, K., Baker, B.
BirdLife International (2023) Species factsheet: Procellaria westlandica. Downloaded from http://datazone.birdlife.org/species/factsheet/westland-petrel-procellaria-westlandica on 07/12/2023.
Recommended citation for factsheets for more than one species: BirdLife International (2023) IUCN Red List for birds. Downloaded from http://datazone.birdlife.org on 07/12/2023.