High levels of seed production (mast) in our beech forests is causing a rodent and stoat explosion that is a serious threat to our endangered native wildlife.

High levels of seed production (mast) in our beech forests is causing a rodent and stoat explosion that is a serious threat to our endangered native wildlife.

New Zealand beech forest. Photo: Jimmy Johnson.
New Zealand beech forest

What is a beech mast?

When beech trees flower they produce large quantities of seed (masts). This happens only once every 2 to 6 years. Masts are triggered by a summer that is warmer than the previous one and by tracking temperatures we can predict when this will occur. 2014 is a mast year.

Beech seed provides good food for rats and mice, which are in turn good food for stoats. During mast years rats, mice and stoats breed prolifically with this abundance of food. The increased number of rats and stoats prey on native birds such as mohua, kākā, kea, whio and kiwi along with other species at risk like bats and land snails.

View the predator plague cycle to see how the beech mast increases predator numbers and how predators turn to birds for food.

Find out more about beech forest in New Zealand.

The need for pest control

When there is no mast, many native birds can tolerate the low levels of rats and stoats present and little or no pest control is necessary.

When mast occurs at just a few sites, only localised pest control is required.

When there is a large beech mast with heavy seed fall, as in 2014, it tends to be widespread, so that rats and stoats have to be controlled over very large areas.

Watch a video about the impact of beech mast on predators and native species.

Why the birds need our help

A widespread beech mast is happening now and without help many native species will suffer dramatic declines over the next year.

Rock wren. Photo: © Sabine Bernert.
Small birds like rock wren are vulnerable to rat predation

Rat sensitive birds

Rapid expansion of the rat population is disastrous for small forest birds, like mōhua.

In the years when stoats and rats are abundant, mōhua breeding is very unsuccessful, and probably 80–90% of birds are killed.

Stoat sensitive birds

Hole- or ground-nesting larger birds like kiwi, kākā and whio, are highly susceptible to stoat predation.

In an exceptional mast year when rats and stoats are at plague proportions, these birds are often caught on the nest by stoats and if the adults are not killed, the eggs or chicks are easy prey.

Larger birds that are too big for rats are killed by stoats. These include: kiwi, kaka and blue duck/whio.

Kea. Photo: © Sabine Bernert.
Larger birds like kea are at risk from stoats

After a stoat plague, the birds recover relatively quickly until the next one, but over a longer period of time there is a steady decline.

Rat and stoat sensitive birds

These are all the smaller birds that both rats and stoats can eat. There are many of these species, including mōhua, titipounamu/rifleman, toutouwai/robin, orange-fronted kākāriki and korimako/bellbird.

Stoats and rats are a catastrophic combination. There is a much larger impact on smaller birds when both rat and stoat plagues happen at the same time. The populations decline more quickly.

More about the effects of introduced predators in New Zealand.

What we're doing

Well timed and planned operations of aerial 1080 is DOC’s best chance of protecting our birds from this fate. 

Get information on 1080 in New Zealand.

DOC has confirmed the prediction of a beech mast by shooting beech tree branches and counting seeds.

  • Very heavy seed falls will occur in The Catlins and Northern South Island.
  • Moderate seed falls will occur in Eastern Fiordland and West Otago.

Confirming the beech mast diagram.

Measuring predator numbers and taking action

By late May, rotent and stoat abudances were measured through our extensive tracking lines.

DOC has since planned 22 predator control operations to knock down rising predator numbers. We will be using aerially applied 1080 over about 600,000 hectares of conservation land.

Read more about what DOC's doing to protect species at risk.

Beech mast impact on predators and native species

In this short video DOC Scientist Graeme Elliot talks about beech mast and predator cycles and the serious threat it poses to our endangered native wildlife.

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