Possums, stoats and rats stripping New Zealand’s forests – Poisoning debate
09/07/2008 11:50:17 July 2008. Introduced mammalian predators and pests, such as possums, rats and stoats, present a huge threat to native forests and wildlife in New Zealand, many of which are being eaten into extinction.The "silent forests" have lost their bird song due to the destruction of introduced animal predators, and not 1080 says Colin Giddy, of the New Zealand Department of Conservation (DOC). "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.
80 million years with no predators
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, 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 poison
1080 is currently considered to be 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 1080 drops
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 per hectare; 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.
Water samples
"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.
