Chatham Petrel (Pterodroma axillaris) breeds only in the Chatham Islands, New Zealand, where it is restricted to South East Island (= Rangatira), Pitt Island and main Chatham Island, having been reintroduced to both of the latter two.
P. axillaris is currently listed as Endangered under Criteria A2bde+4bde as the result of a rapid decline. Significant declines occurred during the 20th century and continued into the 1990s, precipitated by competition with Broad-billed Prions Pachyptila vittata for burrow space (Was et al. 2000). The decline was crudely estimated in 2009 to have occurred at a level of 1% per annum, suggesting a gross decline of approximately 50% over three generations (47 years, based on a generation length of 15.6 years) (G. Taylor in litt. 2009).
Since 1997, control of prions at known petrel burrows, a practice replaced by use of burrow flaps since 2001, has greatly improved nesting success. Productivity on South East Island has improved from 10% to 30% in the early 1990s to a mean of 80% in 2000-2010 (Gummer et al 2014). Additionally, between 2002 and 2006 the species was reintroduced to the 40ha Ellen Elizabeth Preece Conservation Covenant on Pitt Island and from 2008–2011 to the 7.5ha Sweetwater Conservation Covenant on main Chatham Island. Breeding at Pitt Island was first recorded in 2005/6, with 13 pairs breeding on the island by 2009/10 (Gummer et al. 2014). Breeding on the main Chatham Island commenced in 2011/12 (P. Scofield in litt. 2012; G.Taylor in litt. 2007, 2012).
Following these conservation interventions, the total population of P. axillaris has now recovered from 600-800 birds in 1995 to 1,000-1,100 individuals in 2004 and about 1,400 birds in 2010 (based on mark-recapture and burrow survey analysis; G. Taylor in litt. 2009, 2012). The population continues to increase and birds have been colonising formerly occupied parts of South East Island (K.J. Wilson in litt. 2012; G. Taylor in litt. 2012). 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 (G. Taylor in litt. 2012).
The continued increase in P. axillaris population numbers is dependent on the continuation of conservation action (K.J. Wilson in litt. 2009; Robertson et al. 2013). The South East Island population will require continued management through exclusion of Broad-billed Prions from nest burrows. The populations on main Chatham Island and Pitt Island are both protected by predator-proof fencing which requires ongoing management (K.J. Wilson in litt. 2009). Alien invasive mammals will remain a constant potential threat to these sites.
Although dependent on conservation action, the continued population increase of P. axillaris 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). The species therefore no longer qualifies for Endangered status under Criteria A2 or A4. The reduction is still likely to be greater than 30%, so the species is eligible to be listed as Vulnerable under Criteria A2 and A4. Additionally, even taking into account the new breeding areas at main Chatham Island and Pitt Island, the species occupies less than 20km2 and breeds at only three locations (South East Island, main Chatham Island and Pitt Island). The species thus also qualifies for Vulnerable status under Criterion D2. It is therefore proposed to downlist P. axillaris to Vulnerable under Criteria A2+4 and D2.
Additional information and comments on this proposal are welcomed.
Gummer, H., Taylor, G., Wilson, K. J., & Rayner, M. J. 2014. Recovery of the endangered Chatham petrel (Pterodroma axillaris): A review of conservation management techniques from 1990 to 2010. Global Ecology and Conservation, http://dx.doi.org/10.1016/j.gecco.2014.12.006
Robertson, H.A., Dowding, J.E., Elliott, G.P., Hitchmough, R.A., Miskelly, C.M., O’Donnell, C.F.J., Powlesland, R.G., Sagar, P.M., Scofield, R.P. & Taylor, G.A. 2013. Conservation status of New Zealand birds, 2012. NZ Threat Classification Series 4.
Was, N., Sullivan, W. & Wilson, K.-J. 2000. Burrow competition between broad-billed prions (Pachyptila vittata) and the endangered Chatham petrel (Pterodroma axillaris). Department of Conservation, Wellington.