by John Ogden
Great Barrier's Mission Impossible - or is it?
In this issue we feature an article by
James Frankham, editor of the New Zealand Geographic, in which he
outlines the deliberations of a group of scientists and conservationists
meeting to consider the possibilities of eradication of all mammalian
pests from the whole of New Zealand. Apparently independently, Rebecca
Priestley (Science, The Listener, April 14, 2012) reports on the vision
of Sir Paul Callaghan to capitalise on our real point of difference in
the world by ridding New Zealand of all its mustelids, rats, rabbits,
possums and other mammalian pests. Sir Paul was one of New Zealand’s
leading thinkers, and his views, while “crazy and ambitious” were backed
up by an outlined plan to achieve the goal. The theme is taken up again,
by the editor of The Listener (April 21, 2012), under the heading: “The
duty to dream – New Zealand’s unique habitats and species are our
John Innes, an ecologist with a lifetime
of solid published research in this field, reports that every year 26
million native birds are killed by mammalian predators. This is a
staggering figure, but it is probably conservative. In an Email to our
local politician and conservationist, councillor Mike Lee, Innes gives
the maths, based on a published review of 24 research projects involving
13 native forest bird species – see box.
If we do the same estimates for Great
Barrier, assuming the area of scrub and forest is 24,294 ha and that
(conservatively) there are only four nesting attempts per ha, we
conclude that we are loosing 86,500 native birds to rat and cat
predation on Great Barrier every year.
Scientifically, the precise figures mean
diddley-squat, but they surely give us, the public, cause for concern –
they are based on conservative estimates and are certainly of the
correct order of magnitude – they explain why so many species have gone
extinct and why bird populations explode so quickly when predators are
The forests of Great Barrier Island may
still look beautiful to visitors, but: “Basically our forests are dead.
Yes, there are still trees in them, but they’re quiet. The birds are
gone, they’re totally changed because of introduced mammals” (Charles
Daugherty, professor of ecology at Victoria University.) Our recent
submission to the Local Board Long Term Plan emphasised the need to
address the on-going nature of bird extinctions on Great Barrier with
urgency. Since Hutton’s list was made in 1868, Great Barrier has lost 12
bird species, three of these within living memory (whitehead, 1950s;
rifleman, 1970s; kokako 1996). A further three bird species are just
hanging on here, with populations so small that they could be gone next
year (tomtit, kakariki and bittern). The Island has a further 18 birds
in the nationally endangered, vulnerable or declining categories, and an
additional 12 ‘rare’ birds. We are not turning the tide – we’ve been
loosing species continuously since 1868, and there is every indication
that we’re likely to loose more very soon unless a serious, and
successful, effort is made to reduce predators. Our birds could be one
of our great tourist attractions, creating local employment, attracting
visitors and stimulating the economy, but a long-term plan with a vision
of cooperation between all stakeholders is needed to achieve this.
1. Area of native forest in NZ =
2. Average 5 native bird nests per
ha per annum = 29,900,000 nesting attempts per annum
3. Mean failure rate (Table 3 in
Innes et al. 2010) = 73% = 21,827,999 failures
4. If average 2 eggs or chicks per
nest = 42,654,000 dead eggs or chicks
Photo by D Mudge, DOC
5. On average 61% of failures were
due to mammalian predators, therefore:
26,628,940 eggs or chicks of
native birds lost each year due to mammalian predators.
From: Innes, J., Kelly, D., Overton, J. M. & Gillies, C.
2010. Predation and other factors currently limiting New Zealand
forest birds. New Zealand Journal of Ecology 34 (1):86-114.
See also: www.newzealandecology.org.nz/nzje/.