Justification of Red List category
This species qualifies as Vulnerable because the population is restricted to a very small area when breeding, and remains at risk from the accidental introduction of predators and other catastrophes. If it succeeds in expanding its range, it may be downlisted to Near Threatened.
The total population is estimated at 2.5 million birds (Marchant and Higgins 1990), although this estimate is likely too high (G. Taylor in litt. 2012, Waugh et al. 2013).
Pigs were exterminated on Aorangi in 1936 and the population has increased since then, although it is now suspected to be stable or even decreasing (G. Taylor in litt. 2012, Waugh et al. 2013).
Ardenna bulleri breeds only at the Poor Knights Islands, New Zealand. The species is restricted to two main islands, Aorangi and Tawhiti Rahi, and five other islets and stacks (Marchant and Higgins 1990). In the 1980s, one pair was found breeding on the Simmonds Islands, in the far north of New Zealand (Taylor 2000). Between 1938 and 1981, the population on Aorangi increased from c.200 to c.200,000 pairs (Harper 1983, Heather and Robertson 1997). However, surveys in 2011-13 suggested that there are around 100,000 burrows, similar to estimates from Bartle in 1960s (Waugh et al. 2013). In 2011, breeding success on Aorangi Island was noted to be very low, with only 16 chicks found in the 150 burrows sampled (G. Taylor in litt. 2012). The total population has been estimated at 2.5 million birds (Marchant and Higgins 1990), although this now regarded as too high (G. Taylor in litt. 2012, Waugh et al. 2013). The species migrates to the northern Pacific Ocean, from Japan to North America and east to California, and is occasionally found off South America (Heather and Robertson 1997, Taylor 2000). The main non-breeding moult zone appears to be the Emperor Seamounts, a chain of underwater volcanos northwest of Hawaii (G.Taylor in litt. 2016).
It nests in burrows or on rock-crevices and ledges, often under dense vegetation. It feeds on krill, small fish, salps and jellyfish (Marchant and Higgins 1990, Heather and Robertson 1997).
This species is at risk from bycatch throughout its range. It was previously caught in north Pacific drift-nets (Gould et al. 1998), and is still potentially at risk from set-nets. It may be caught on longlines, in trawling operations and on hand and reel lines, but bycatch levels have not been quantified and documented evidence is scarce (Taylor 2000, Tennyson et al. 2012). In recent decades, the Hauraki Gulf has been subject to intensive purse-seine fishing of pelagic fish which has interfered with an important foraging area and may have impacted the species through food resource depletion. Perhaps as a linked effect of this fishery, populations of Red-billed Gulls Larus scopulinus on the Mokohinau Islands have crashed from c.20,000 birds in the 1960s to fewer than 500 birds in 2011 (G. Taylor in litt. 2011). Further investigation is required. In addition, climate change is anticipated to have a significant effect on this species due to its limited range (the population is restricted to an islands with a maximum altitude of 218 m [BirdLife International unpubl. data]), and its observed sensitivity to climatic fluctuations and apparent lower productivity during La Niña years. The poor breeding success recorded on Aorangi Island in 2011 may have been related to a strong La Niña event in 2010-2011, but data from some birds fitted with geolocators indicated that incubation shifts were around twice the length of those published in the 1980s (G. Taylor in litt. 2012). Domestic Pigs Sus domesticus were previously present on Aorangi Island, but eradicated in the 1930s, when the island was declared a reserve. Vegetation and soil conditions has subsequently greatly improved (Heather and Robertson 1997).
Conservation Actions Underway
The eradication of pigs from Aorangi in 1936 caused a massive increase in the population, with the recolonisation probably coming from the nearby predator-free island, Tawhiti Rahi (Heather and Robertson 1997). Fishing has been banned at the Poor Knights Islands Marine Reserve since 1996 and entry onto the island reserve is prohibited (M. Szabo in litt. 2004). The International Maritime Organisation (IMO) established the world's first mandatory area to be avoided for large shipping vessels, including oil tankers, around the islands in 2004 (M. Szabo in litt. 2004). Breeding islands have permanent poisoned bait stations and each island is checked every year for any evidence that rodents have arrived (G. Taylor in litt. 2012). The species has been the subject of tracking studies utilising geolocators (2011-2013). These data show the birds are a pelagic species, making extensive use of oceanic seas well east of the North Island (including the Louisville Ridge), and also the Chatham Rise and Bounty Trough (east of the South Island) during the breeding season and migrate to the Emperor Seamounts in the NW Pacific Ocean during the austral winter (G. Taylor in litt. 2016).
Conservation Actions Proposed
Complete an accurate population census (including on Aorangi Island), to better assess breeding numbers (Waugh et al. 2013), assess the current status of breeding on Simmonds Islands and identify any signs of prospecting on other island groups. Establish monitoring plots on Poor Knights to determine the rate and pattern of colony expansion (Taylor 2000). Quantify the impact of bycatch during fishing activities and also assess whether competition with commercial fisheries for surface shoaling fish may be affecting the breeding population. If judged necessary, work with fisheries to develop bycatch reduction measures.
46 cm. Large, grey, black-and-white shearwater with broad wings, buoyant flight and wedge-shaped tail (normally folded). Blackish-brown head, neck. Grey wings, back with large dark M across wings. Grey uppertail with black tip. White underparts, underwing. Slim, grey bill with dark tip. Similar spp. Unlike any other Pacific shearwater. Juan Fernández Petrel Pterodroma externa has dark leading edge to underwing. Voice Generally quiet at sea. Assorted howlings, wailings at colony. Calls are very similar to those of Sooty Shearwater P. griseus (G. Taylor in litt. 2012).
Text account compilers
Stuart, A., Taylor, J., Benstead, P., Hermes, C., Calvert, R., Mahood, S., Fjagesund, T., Martin, R., McClellan, R., Moreno, R.
Taylor, G.A., Tennyson, A., Szabo, M.
BirdLife International (2023) Species factsheet: Ardenna bulleri. Downloaded from http://datazone.birdlife.org/species/factsheet/bullers-shearwater-ardenna-bulleri on 30/09/2023. Recommended citation for factsheets for more than one species: BirdLife International (2023) IUCN Red List for birds. Downloaded from http://datazone.birdlife.org on 30/09/2023.