Birdlife explosion as possum numbers slashed

A dramatic drop in the estimated possum population is good news for native birds.

New research shows possum numbers have plummeted from between 60 and 70 million during the 1980s, to about 30 million.

The Wellington region recorded the biggest drop, of 87 per cent.

The region has about 200,000 possums, but without possum control the number would have been between 1.3 and 1.5 million.

Forest and Bird spokeswoman Helen Bain said the drop was a factor in exploding numbers of tui in the Wellington area. "We're getting a lot of anecdotal reports that numbers are up. I was in town the other day and I would have seen about 20 of them."

Possums would raid the nests of native birds, such as tui, taking eggs, chicks and sometimes even adult birds, she said. "If we get possum numbers down, native birds and plants come back big time."

The study, by Landcare Research wildlife biologist Bruce Warburton, used satellite-imaging technology to analyse 52 vegetation types, which helped show how many possums each area could accommodate.

The Conservation Department and regional councils also provided information.

The study found the forests could host 48 million possums, with no pest control. But when efforts to beat possums were included, that figure dropped to 30 million. "New Zealanders have been fascinated by how many possums there are, ever since the estimates of 60 to 70 million were generated in the 1980s."

Australian brush-tailed possums, introduced in 1837 to establish a fur trade, have become New Zealand's main pest in both ecological and economic terms.

Among their favourite foods are the leaves of natives trees such as pohutukawa and totara.

Possum control is carried out on about 13.3 million hectares – about half all vegetated land – for conservation and to stop the spread of bovine tuberculosis. The Conservation Department spent $14.9 million on it last year, mainly using 1080 poison.

The results of the study did not mean the war against possums was over, DOC spokesman Rory Newsman said. "We are getting some good results in places, but there is constant re-invasion by possums."

- © Fairfax NZ News