Archived 2015 topics: Chatham Petrel (Pterodroma axillaris): Downlist to Vulnerable?

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.

References

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.

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4 Responses to Archived 2015 topics: Chatham Petrel (Pterodroma axillaris): Downlist to Vulnerable?

  1. W.R.P. Bourne says:

    It seems possible that before the arrival of man the Chatham Petrel may have had a very large population dispersing to a large part of the Pacific. There is therefore a neede for continuing conservaqtion to restore this situation.

  2. Graeme Taylor says:

    I agree with the decision to downlist this species to vulnerable. Since burrow management intensified from 1997, the colony on Rangatira has produced a large of number of chicks and there has been steady recruitment of these birds into the breeding population. Using spotlighting techniques at the main aerial courtship area, we have found that the majority of birds caught are now banded and are returning chicks from our managed burrows. But more importantly the numbers seen and caught in similar weather conditions has increased over time. In the early to mid-1990s catching 1-2 birds on a good night was typical and catching 8 birds was exceptional. In recent trips (2008-2012), 10-16 birds can be caught on good nights. Most of these banded birds are not found later in the known burrows so it is assumed these are recruiting elsewhere on the island. Currently the cost of managing a increasing pool of new breeding pairs is too expensive with current resources available to NZ Conservation Dept. So the project goal is to continue to maximise productivity from the pool of about 150 mapped and managed burrows. Ongoing population expansion will be dependent on these managed breeding burrows producing chicks plus a limited number of chicks being reared from unmanaged sites. The numbers breeding on the two newly established sites on Pitt Island and Chatham Island are still low. To delist from vulnerable I think there will need to be evidence of sustained population growth at these new sites and perhaps as many as 50 pairs established at both sites before this step is made.

    In reply to Bill Bourne, Alan Tennyson at Te Papa Museum examined sub-fossil bone deposits on Pitt Island and has found that P. axillaris was one of the most abundant species on that island in the past. Recent tracking studies using archival tags (geolocaters) published by Rayner et al. 2012 (in Emu) has shown that the Chatham petrel population migrates to the eastern Pacific in the austral winter and spring. They utilise an area of deep oceanic water over the Nazca sea ridge and up the Humboldt current to the seas near the Galapagos Islands.

  3. Andy Symes (BirdLife) says:

    Preliminary proposals

    Based on available information, our preliminary proposal for the 2015 Red List would be to list:

    Chatham Petrel as Vulnerable under criterion A2be+4be; D1+2.

    There is now a period for further comments until the final deadline of 31 August, after which the recommended categorisation will be put forward to IUCN.

    The final Red List categories will be published on the BirdLife website in late October and on the IUCN website in November, following further checking of information relevant to the assessments by both BirdLife and IUCN.

  4. Andy Symes (BirdLife) says:

    Recommended categorisation to be put forward to IUCN

    Following further review, there have been no changes to our preliminary proposal for the 2015 Red List status of this species.

    The final categorisation will be published on the BirdLife website in late October and on the IUCN website in November, following further checking of information relevant to the assessment by BirdLife and IUCN.

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