Rats rampage in the Ruahines
The rat population in a piece of pristine bush has exploded thanks to a plethora of beech tree seeds, forcing the Department of Conservation to make a 1080 drop.
But the glut of food means it can be difficult to get rats to eat the poison.
A department spokeswoman said monitoring showed massive rat population growth in the northern areas of the Ruahine Forest Park, running up the centre of the North Island from Palmerston North to just north of Taihape. Monitoring was done by placing equipment in rat tunnels.
The threshhold for planning a 1080 drop was getting rats in 20 per cent of tunnels laid to measure the rat population, but testing showed rats in 61 per cent of tunnels in the Ruahines in May, the spokeswoman said.
That was not as bad as some parts of the country, with areas of Nelson hitting 80 or 90 per cent.
The last 1080 drop in the Ruahines took place in November 2017, which saw the rat tracking go from 11 per cent in June 2017 to 1 per cent in May 2018.
Numbers stayed relatively low until August 2018, but climbed to 27 per cent in February before the big May jump, she said.
A rat population that large in a higher altitude area such as the northern Ruahine Forest Park was unusual.
The problem was not isolated to the Ruahines, though, with various New Zealand forests experiencing the same issue due to beech trees experiencing a heavy seeding, known as a mast.
The spokeswoman said a mast happened when there was a cool summer followed by a hot summer, encouraging beech flowering and subsequent seed production. That seed was great for some native birds such as ka¯ka¯riki, but rats also ate the seed.
Stoats were also a problem, because females could raise their embryo count if they knew there was more food around, the spokeswoman said.
‘‘It’s a double whammy of hungry rats and more stoats.’’
Getting 1080 in before then, along with other pest eradication methods such as trapping, would give native animals a better chance of survival, she said.
It was not guaranteed to work, though, because some parts of New Zealand had so much beech seed the rats were ignoring 1080, she said.
‘‘It is a really beautiful remote area with lots of species we want to look after,’’ the spokeswoman said.