Justification of Red List Category
This species has been downlisted to Vulnerable because although its population has undergone a rapid decline over the past three generations and it is restricted to just three locations, the population has been increasing since 2000 owing to intensive conservation action including two translocations, such that the decline over the past three generations has no longer been very rapid.
Based on an age at first breeding of three years, and an estimate that at least 75% of birds will be over three years old, the latest total population estimate from 2010 of c. 1,400 individuals probably includes c. 1,100 mature individuals (Gummer et al. 2015).
Occupied burrows and the number of surface birds declined at areas in common usage in the 1930s, into the 1990s. Intense, sometimes lethal, competition with Broad-billed Prions Pachyptila vittata for burrow space precipitated recent declines, crudely estimated at 1% per annum equating to approximately 50% over the past three generations. Since 1997, however, control of prions at known petrel burrows, a practice replaced by use of burrow flaps since 2001, has greatly improved nesting success and the population is now increasing; a trend boosted by two recent and successful translocations to predator free conservation covenants on Pitt Island and Chatham Island. The total population has now recovered from 600-800 birds in 1995 to about 1,400 birds in 2010 (based on mark-recapture and burrow survey analysis) (Gummer et al. 2015). The population continues to increase and birds have been colonising formerly occupied parts of South East Island (G. Taylor in litt. 2012, K.J. Wilson in litt. 2012). Although dependent on conservation action, the continued population increase makes it likely that the population size reduction over the past three generations (47 years) is now less than 50% (G. Taylor in litt. 2012). However the reduction is still likely to be greater than 30%.
This species is restricted to South East Island (= Rangatira) and two predator protected sites on Pitt Island and Main Chatham Island in the Chatham Islands, New Zealand, having been reintroduced to both of the latter two (Gummer et al. 2015). Subfossils indicate that it was once more widespread, being present on Mangere Islands (A. J. D. Tennyson per P. Scofield in litt. 2012). The earliest estimate of 50 birds was later revised to 200-400 (Marchant and Higgins 1990). A mark-recapture census in 2004 estimated that the global population stood at 1,000-1,100 individuals comprising 250 breeding pairs, a floater population of adults unable to breed each year owing to loss of partners or nesting sites, and juveniles aged up to five years (Taylor 2000, G. Taylor in litt. 2009). The total population was estimated at 1400 birds in 2010 (Gummer et al. 2015). The increase reflects an improvement in knowledge and since 2000, a marked response to successful management with over 100 chicks now fledging annually and many recruiting back to the island.
Significant declines occurred during the 20th century and continued into the 1990s; an annual decline of 1% per annum has been crudely estimated and cautious interpretation suggests a gross decline of 40-50% or more may have occurred over the past three generations (G. Taylor in litt. 2009). Trends appear to have stabilised since 2000, prompted by successful conservation measures. Between 2002 and 2006, 200 chicks were moved to a newly created predator-free site on Pitt Island; successful breeding first occurred in 2006 (Anon 2006), and 17 pairs were present in 2012 (G. Taylor in litt. 2012). Numbers halved at this site after a predator incursion event in 2013 (G. Taylor pers. comm.). About 200 chicks were transferred to the 2.4-ha Sweetwater Conservation Covenant on the main Chatham Island between 2008 and 2011. The first breeding attempt at this site occurred in 2012 (G. Taylor in litt. 2012, Bell et al. 2013). Tracking research conducted in 2009/2010 using geolocators has shown that birds feed mainly south and east of the Chatham Islands during the breeding season, with the Bollons Seamount being important during chick rearing (Rayner et al. 2012). The species migrates to the eastern Pacific in winter to an area over and north of the Nazca sea ridge, about 1,000-1,500 km west of Chile and Peru (Rayner et al. 2012).
It nests in burrows in very friable densely burrowed soils in lowland temperate forest and scrub, on flat to moderate sloping ground (Marchant and Higgins 1990). Its diet is not well known but includes squid and small fish. Some young have returned to the island at two years old (Heather and Robertson 1997), and breeding has been recorded at the age of three, although most individuals do not breed until five years of age (G. Taylor in litt. 2009). Much of the life cycle is spent at sea; birds return to land only to breed. Visits to the colony occur after dark.
On South East Island, intense competition for burrows with the abundant Broad-billed Prion Pachyptila vittata (including lethal attacks on chicks and eggs, and occasionally adults) is the primary threat (Was et al. 2000). Such competition may be the cause of the observed low breeding success and high rate of pair-bond disruption. On the other islands in the group, exploitation by humans for food and introduced predators were the probable causes of extirpation (Taylor 2000). Predator-proof fencing has facilitated translocations to two Conservation Covenants on Pitt Island and Chatham Island; alien invasive mammals will remain a constant potential threat to these sites and on-going management will be required.
Conservation and Research Actions Underway
South East Island has been managed as a reserve since 1954, and cattle, sheep and goats were removed in 1961 (Marchant and Higgins 1990, Taylor 2000). Intensive research, on-going since 1991, helped to identify the impact of Pachyptila vittata. As a consequence, artificial nest-sites have been provided and burrows have been blocked to prevent occupation by P. vittata during the absence of Pterodroma axillaris. P. vittata found occupying P. axillaris burrows are culled (Taylor 2000). Since 2001, neoprene burrow flaps installed at burrow entrances have greatly reduced prion impacts during the period February to April (Sullivan and Wilson 2001). These measures have greatly improved breeding success (Taylor 2000), from 10-30% in early 1990s to a mean of 80% in 2000-2010 (Gummer et al. 2015). Intensive burrow searches have now located over 160 active breeding sites of the estimated 250 pairs using the island. All newly located burrows are converted to artificial nest sites and are safe-guarded from prion interference. The project aims to maintain and maximise productivity from approximately 150 mapped and managed burrows per annum (G. Taylor in litt. 2015).
In 2002, a second population was created in a predator free enclosure on the 40-ha Ellen Elizabeth Preece Conservation Covenant (EEPCC). Over a period of four years, 200 chicks were transferred to this site, and by 2006 four birds had returned with a pair successfully rearing a single chick for the first time (Gummer et al. 2015). In 2006-2007, four pairs nested and four chicks were reared. This included one pair of unbanded birds that have been lured presumably to the site by the sound attraction system. In 2008, seven chicks fledged from the EEPCC. Damage to the predator fence after a storm in 2013 resulted in a feral cat incursion and loss of some Chatham petrel breeding pairs before the damage was detected. Numbers are now rebuilding. About 200 chicks were transferred to the 2.4-ha Sweetwater Conservation Covenant on the main Chatham Island between 2008 and 2011. In 2015-1016, 9 new burrows were found using trained seabird dog. The breeding population is composed of 6 breeding pairs, with 4 further pairs breeding just outside the fence.
In 2009-2010, 22 geolocation tags were applied to breeding Chatham petrels and 18 were recovered. This species migrates to the eastern Pacific Ocean off Peru between May and Oct (Rayner et al. 2012).
Conservation and Research actions
Proposed Monitor breeding burrows annually ateach of the three sites and mark all chicks. Continue to protect nesting birds from prion interference. Ensure pairs nesting at the transfer sites are secure from predator incursions by maintaining fences and protect any pairs nesting outside the fences. Survey needed of population trends on Ranagtira Island.
30 cm. Small, grey-and-white gadfly petrel with unique underwing pattern. Dark grey crown, sides of face and neck. Black mark behind eye. Grey upperparts. Grey tail with dark tip. Grey upperwing with dark, moderately distinct M. Pale grey half-collar at sides of breast. Rest of underparts white. White underwing with dark tip, broad, black bar extending from axillaries (where broadest) to carpal joint, then less prominently towards tip. Similar spp. Black underwing bar of Black-winged Petrel P. nigripennis does not reach body and axillaries. Larger Mottled Petrel P. inexpectata has bold bar, but has dark centre to belly. Voice Flight call whis-whis-whis, oi, purring call given on ground.
Text account compilers
Anderson, O., Ashpole, J, Benstead, P., Bird, J., Calvert, R., Lascelles, B., McClellan, R., Moreno, R., Taylor, J., Temple, H.
Wilson, K., Tennyson, A., Scofield, P., Taylor, G.A., Bourne, W., Hitchmough, R., Bell, M.
BirdLife International (2018) Species factsheet: Pterodroma axillaris. Downloaded from http://www.birdlife.org on 23/07/2018. Recommended citation for factsheets for more than one species: BirdLife International (2018) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 23/07/2018.