Rakitu, Rats and Weka - moving ahead in 2017
by John Ogden & June Brookes
Four years since the Government allocated funding for rat eradication on Rakitu, no discernible progress has been made. Will there be any real action in 2017?
North Island weka1 were introduced to Rakitu in 1951 and have increased in number since then. Elsewhere in the North Island, weka populations have suffered dramatic declines2. The species was regarded as ‘threatened’ in 1991, and classified as ‘Category B’ (second priority for conservation action) in 1994, although some recommended an upgrade to ‘Category A’. More recently, weka have been classified as ‘Nationally Vulnerable B’3.
Weka population trends
Figure 1. The weka population on Rakitu has increased exponentially since 19514,5,6.
The slow exponential increase in weka numbers on Rakitu (Figure 1), is consistent with low reproductive rates of one or two chicks per pair2. A healthy weka population probably survives on Rakitu and there is good reason to be concerned that it will be put at risk if rats are eradicated by an aerial toxin drop. Drastic reductions in weka numbers have occurred elsewhere following such actions, as weka eat the rat baits.
The Weka Recovery Group provides advice to the Operations Group within the Department of Conservation. This latter group makes decisions which presumably then influence the local allocation of resources. With reduced capacity generally within DOC, and notably on Great Barrier Island, a discussion of the wider picture of ecosystem recovery on Rakitu is required with community involvement encouraged as much as possible.
Prime location on the seabird super highway
Weka mainly feed on forest-floor invertebrates, including rare native snails7. Some tree berries are also eaten on the ground, potentially reducing forest recovery in areas opened up by cattle grazing. Weka also feed on the young of ground-nesting birds, so re-establishment by many species of petrels and shearwaters is likely to be inhibited if weka are present.
A rat-free Rakitu offers exciting potential to link...sea-bird nesting colonies on offshore islands...
As stressed by Waterhouse (2012)8, the absence of nesting seabirds from the forests of New Zealand – and especially Aotea/Great Barrier – is one of our least appreciated or understood losses of biodiversity. A rat-free Rakitu offers exciting potential as a link in a chain of sea-bird nesting colonies on offshore islands stretching from the rat-free Poor Knights to rat-free Cuvier Island.
Grey-faced petrel, Cook’s petrel and diving petrel on Rakitu were once an abundant source of food for Maori—now no seabirds are known to nest on the island. Experience from elsewhere indicates that these species and others, such as the fluttering shearwater, would surely return if predators, including weka, are removed.
Forest regeneration, and forest ecosystem diversity, would also be improved. Since weka were introduced, whitehead, bellbird and red-crowned parakeet have become extinct on Rakitu. The cause(s) of these extinctions are not known. Ship rats are implicated, although birds survived with rats present for a century from 18689 to 19575. Habitat loss could also be a factor, as much forest cover has been lost as a result of grazing cattle. Rat eradication and weka removal must be accompanied by ecosystem restoration, particularly given the rampant growth of kikuyu grass, which inhibits natural forest regeneration.
Little progress since 1993
The matter of rat eradication on Rakitu has been simmering since 1993. Initially, it appeared to be local Aotea/Great Barrier concerns about the lessees grazing cattle. Since 1999, the important role that Rakitu plays in the security of the North Island weka population has been recognised, complicating planning towards rat eradication.
The north-west side of Rakitu Island—the Acquisition Proposal to the Forest Heritage Fund stated that ‘Rakitu has the advantage of relatively few introduced mammalian predators......Eradication of ship rats...would allow many remaining native fauna species to recover and increase in numbers12. Photo: E. Waterhouse
Where there are clearly conflicting conservation values, surely some leadership is needed from the Department of Conservation’s Head Office? And for all relevant parties to meet and map out a way forward. Such an approach is ‘far more likely to succeed in achieving on-the-ground benefits than relying on managers and academics working independently’10.
There are options
If the problem is simply finding a new location for 50 weka, then here are some suggestions:
· Find, or create, a predator proof area, preferably on the mainland (Gisborne)
· Move the weka to Kawau Island to diversify the gene-pool there.
· Approach trustees of Motu Kaikoura — to establish a weka population. By setting up fenced controls, this option could be planned to measure the role of weka in island restoration.
Rakitu Timeline - a study of lost opportunity?
1867 Report on birds of Great Barrier by Hutton & Kirk. Weka not recorded9.
1883 Ngati Rehua sell Rakitu to Europeans.
1951 Thirteen weka introduced to Rakitu from Gisborne by the Department of Internal Affairs5.
1957 Estimated 20-40 weka on Rakitu5.
1981 Offshore Islands Research Group recorded ‘at least’ 60 weka6.
1992 At least 109 and possibly up to 135 weka11.
1993 The Acquisition Proposal to the Forest (later Nature) Heritage Fund drawn up.
Rakitu acquired into public ownership (Department of Conservation) at a cost of $1.8 million. Purchase
described as an ’exceptional opportunity’12 for rat eradication.
1999 Publication of Weka Recovery Plan2. Weka Recovery Group stated that rodent eradication should not occur
until another North Island weka population was established.
2002 Up to 240 weka8 on Rakitu.
2011 Great Barrier Island Charitable (now Environmental) Trust Strategic Plan 2011-13 gave a top priority to an
early start on tree planting and pest management on Rakitu.
2013 Former Minister of Conservation, Nick Smith, announced “...a commitment of $190,000 from the Nature Heritage Fund to rid Rakitu of rats”.
2014 Planned eradication of rats from Rakitu confirmed by the Department of Conservation. Major storms/floods severely damaged island infrastructure, with Department staff and funds diverted elsewhere.
2015 Weka Recovery Group opposed to rat eradication (using aerial toxins) until such time as a suitable site for translocation of 50 weka from Rakitu can be identified.
2016 Slow progress with Rakitu rat eradication reviewed by Brookes14.
2017 Paul McArthur (Department of Conservation) reports planning for rat eradication has recommenced - but is unlikely to occur until winter 2018—and weka may not be removed.
Acknowledgments: Thanks to Paul McArthur, Area Manager Great Barrier Island, for discussion of an earlier draft of this article. Thanks also to Councillor Mike Lee for persistently raising the issue of rat eradication on Rakitu.
Notes:
1Visitors to Great Barrier often think banded rails are weka - the two species are related, but weka are bigger.
2Beauchamp, A. J. et al. 1999. Weka (Gallirallus australis) Recovery Plan 1999-2009. Threatened Species Recovery Plan 29. Department of Conservation. Wellington.
3MisKelly, C. M. & Powlesland, R. 2013. Conservation translocations of New Zealand birds. 1863-2012. Notornis 60: 3-28.
4Beauchamp, A. J., Blick, A. J. & Chambers R. C. 2002. Report. Dept. of Conservation. Great Barrier Field Office Archives.
5Bell, B. D. & Braithwaite, D. H. 1964. The birds of Great Barrier and Arid Islands. Notornis 10: 363-383.
6Bellingham, P. J., Hay, J. R., Hitchmough, R. A. & McCallum, J. 1982. Birds of Rakitu (Arid) Island. Tane 28: 141-147.
7Brook, F. J., McCallum, J. & Cameron, E.K. 1982. A note on the occurrence of Rhytida greenwoodii Grey (Mollusca: Paraphantidae) at Rakitu Island, northern New Zealand. Tane 28: 137-139.
8Waterhouse, K. 2012. Rakitu. Where the light meets the sky. GBIET. Environmental News 29: 8-14.
9Hutton, F. W. 1868. Notes on the birds of Great Barrier Island. Transactions and Proceedings of the New Zealand Institute. Vol. 1. 1869.
10Ewen, J, G., Adams, L. & Renwick R. 2013. New Zealand species recovery groups and their role in evidence-based conservation. Journal of Applied Ecology 50: 281-285.
11Beauchamp, A. J., Chambers, R. & Kendrick, J. L. 1993. North Island weka on Rakitu Island. Notornis 40: 309-312.
12Murray, W. 1993. Ministerial Request Memorandum (93/3294: Rakitu Island).
13Rather than ‘fostered’ the bellbird has become locally extinct since this was written.
14Brookes, J. 2016. Rakitu/Arid Island rat eradication. GBIET. Environmental News 35: 9-10.
Environmental News Issue 37 Autumn 2017