The Department of Conservation has warned that in many parts of New Zealand beech forests flowered heavily in spring.
This mast flowering is the result of particularly warm temperatures in early autumn last year.
A beech flower produces a small seed that drops to the forest floor. After a mast season the number of rats and mice soars because of all the extra food.
Numbers of stoats, which feed on rodents, climb proportionately. Stoats are fast breeders and the number of young they produce varies according to conditions. As the rats and mice run out of seeds and are eaten by the stoats, their numbers fall.
The stoats go in search of other food and often go to the nearest tree hole, where they will find a möhua (yellowhead), käkäriki (parakeet) or käkä.
DOC says this summer’s masting will probably be even bigger than the masting of 2000.
That led to the disappearance of a population of möhua in the Marlborough Sounds and reduced the number of möhua in another group in Fiordland from a few hundred to about a dozen.
DOC says it is looking at target areas for extra predator control to protect birds that could suffer as a result of stoat predation following the beech masting.
Forest & Bird Advocacy Manager Kevin Hackwell says DOC has no choice but to increase the amount of landscape-scale pest control, including aerially applied 1080, particularly in the areas where endangered species like the möhua live. But he says DOC will struggle to adequately respond because of ongoing funding cuts. Forest & Bird will continue to advocate for those cuts to be reversed.