Quiet Forests due to Predators and Pests
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Possum and rat eating baby birds. Photo courtesy of Nga Manu , Waikanae
2 July 2008
Quiet Forests due to Predators and Pests
Introduced mammalian predators and pests such as possums, rats and stoats present huge threats to our native forests and
wildlife, many which are being eaten into extinction.
Today’s “silent forests” which have lost their bird song, are due to the destruction of introduced animal predators not
1080 says Colin Giddy, DOC Kapiti Area Office. “It is the killers of the night, such as possums, rats and stoats, that
are responsible for the loss of native forest canopy and decline in bird species,” comments Mr. Giddy.
New Zealand’s flora and fauna evolved for 80 million years with no browsing or predatory mammals, so they have not
developed any natural defence against these animals. Thus, our native plants and animals are particularly vulnerable.
The tens of millions of brush tailed possums, which eat millions of tonnes of vegetation each year, cause major damage
to forest canopies. Possums also eat birds, eggs, chicks, berries and other native bird food sources. In addition, agile
rats easily climb up trees to dine on unsuspecting native birds sitting on nests.
1080 is currently the safest, most cost efficient and effective way to reduce possum numbers. Research has shown forest
canopy and nesting success of native birds such as kereru, tomtits and robins improves noticeably following aerial 1080
operations. The recovery of forest vegetation after possums are killed also means nectar, berries and other food sources
increase which benefits bird life.
Aerial application of 1080 is currently the most cost-effective method for controlling possums over large areas of
rugged terrain that is extremely difficult to access on foot. Aerial drops of 1080 from helicopters are done with GPS
navigational tools which ensure the correct areas are targeted. Accurate dispersal systems and improved bait design have
resulted in far better knock down of possum and rat populations and a 90% reduction in the amount of 1080 applied per
hectare since the 1970’s.
“We are not indiscriminate in the way we use 1080. It is highly controlled and precise,” says Mr Giddy. The sowing rate
of cereal bait is about 3kg a ha; this equates to about a teaspoon of the pesticide 1080 per ha. 1080 is biodegradable
which means it quickly breaks down into non-toxic substances and does not accumulate in food webs or water.
“There have been 83 water samples taken after aerial application of 1080 bait in the Tararua Forest Park. None of these
samples showed any traces of 1080. This is because the level of 1080 applied is so low and the fact that 1080 breaks
down to natural occurring substances in rivers and streams,” comments Mr Giddy.
“There may be a minor risk to the odd individual bird because of the aerial possum control operation but the increase in
breeding success and lack of predation, allows bird populations to increase to much higher numbers,” commented Mr.
Giddy. 1080 baits are now designed not to break down into small particles that birds are likely to eat; they are also
flavoured with cinnamon and coloured green which makes them less attractive to birds.
DOC – Kapiti Area, plans to reduce possum numbers in 10,585 ha of Tararua Forest Park, which includes the Ohau and
Mangahao catchments, in the first favourable period of fine weather from 21 July 2008. The operation outcome is to
protect the canopy structure, particularly species such as fuchsia, kamahi, totara, and northern rata. Rat control is a
secondary benefit that assists the operation in decreasing native bird and invertebrate predation.
DOC has six canopy protection areas ranging from 5,000 to 11,000 ha. One of these areas will receive possum control each
year. In addition, a biodiversity zone of 4,000 ha within the Otaki catchment will be treated once every three years.
This will be done in spring to target rats as well as possums, providing greater protection to native birds during the
nesting period.
DOC has contacted adjoining neighbours will place warning signs around the boundary prior to the start of the operation.
There is no risk to people visiting the treated area as long as they do not eat the bait.
“Protecting our unique native forest and birds is a never-ending battle. Without the continued use of 1080, the dawn
chorus in many of our forests would become silent due to the ongoing pressures of introduced pests,” says Mr Giddy.
ENDS