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).

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).

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).

Conservation Actions Proposed
Census all burrows every 10 years, continue annual monitoring of study burrows, and band chicks and adults. Identify and minimise hazards to birds flying to and from the colony. Carry out predator control and monitoring of nests to identify predation events, and respond accordingly, and carry out sustained control of browsing mammals, particularly goats and possums. Exclude stock and dogs from colonies (Taylor 2000), e.g. with fencing, bait stations or management of buffer land (Waugh and Wilson 2017). Ensure that local people are aware of the risk posed by dogs (Wilson 2016). Minimise the impact of tourist infrastructure through planning control (K.-J. Wilson in litt. 2008). Maintain vigilance in assessing seabird-fisheries interaction data in New Zealand and other areas to ensure that changes in fisheries operations, gear types and areas of activity do not lead to concomitant changes in bycatch (B. Baker in litt. 2012). Enforce standards around lighting and structures (Waugh and Wilson 2017). Research impact of light pollution on the population (Wilson 2016). Monitor whether human harvest is taking place (Waugh and Wilson 2017).