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
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.
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.
Figure 1. The weka population on Rakitu has
increased exponentially since 19514,5,6.
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.
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
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
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
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.
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.
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.
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
Timeline - a study of lost opportunity?
Report on birds of Great Barrier by Hutton & Kirk. Weka not
1883 Ngati Rehua sell Rakitu to Europeans.
Thirteen weka introduced to Rakitu from Gisborne by the
Department of Internal Affairs5.
Estimated 20-40 weka on Rakitu5.
Offshore Islands Research Group recorded ‘at least’ 60 weka6.
1992 At least 109 and possibly up to 135 weka11.
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
for rat eradication.
Publication of Weka Recovery Plan2.
Weka Recovery Group stated that rodent eradication should not occur
until another North Island weka population was established.
to 240 weka8 on
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.
Former Minister of Conservation, Nick Smith, announced “...a
commitment of $190,000 from the Nature Heritage Fund to rid Rakitu
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.
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.
Slow progress with Rakitu rat eradication reviewed by Brookes14.
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.
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.
to Great Barrier often think banded rails are weka - the two species
are related, but weka are bigger.
A. J. et al. 1999. Weka (Gallirallus
Recovery Plan 1999-2009. Threatened Species Recovery Plan 29.
Department of Conservation. Wellington.
C. M. & Powlesland, R. 2013. Conservation translocations of New
Zealand birds. 1863-2012. Notornis 60: 3-28.
A. J., Blick, A. J. & Chambers R. C. 2002. Report. Dept. of
Conservation. Great Barrier Field Office Archives.
B. D. & Braithwaite, D. H. 1964. The birds of Great Barrier and Arid
Islands. Notornis 10: 363-383.
P. J., Hay, J. R., Hitchmough, R. A. & McCallum, J. 1982. Birds of
Rakitu (Arid) Island. Tane 28: 141-147.
F. J., McCallum, J. & Cameron, E.K. 1982. A note on the occurrence
Grey (Mollusca: Paraphantidae) at Rakitu Island, northern New
Zealand. Tane 28: 137-139.
K. 2012. Rakitu. Where the light meets the sky. GBIET. Environmental
News 29: 8-14.
F. W. 1868. Notes on the birds of Great Barrier Island. Transactions
and Proceedings of the New Zealand Institute. Vol. 1. 1869.
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.
A. J., Chambers, R. & Kendrick, J. L. 1993. North Island weka on
Rakitu Island. Notornis 40: 309-312.
W. 1993. Ministerial Request Memorandum (93/3294: Rakitu Island).
than ‘fostered’ the bellbird has become locally extinct since this
J. 2016. Rakitu/Arid Island rat eradication. GBIET. Environmental
News 35: 9-10.