Sneaky peep at sex lives of forest pests

By ANNE BESTON

A new device has uncovered another undesirable trait to add to the long list of possum peccadilloes - they're promiscuous.

Auckland University researchers carrying out the first in-depth study of the creatures' mating habits have discovered one female can mate with as many as three males in an hour.

"We're getting a real picture of who has been doing what to whom and when," said Associate Professor of Ecology at Auckland University Mick Clout, who is leading the study. Research fellow Dr Ji Weihong is doing field work and co-ordinating the project.

The researchers have invented a "Mate ID" device, which records how many males female possums mate with during the breeding season.

About 10 females have been fitted with the device, which hangs around their necks like a collar and logs visits from male possums.

The males are fitted with electronic radio transmitters and when they move within 40cm of a female wearing the mating recorder possum privacy ends.

The female's device is then plugged into a computer and the data downloaded and interpreted.

If it shows that male number four visited for five minutes on a certain night at a certain time, there can be no doubt about what's been going on - except during the breeding season, female possums are solitary and have nothing to do with males.

"It's a world first. No one has developed anything like it before," said Professor Clout, who has applied to patent the device.

If biological control of possums became a reality, the data gathered during this project could give scientists a better understanding of how effective it might be, he said.

"We need to know how long they are in contact with each other if we use some sort of biological control in the future such as sexually transmitted disease.

"Over 1000 papers have been published on possums but we are still only really starting to find out the details of their mating behaviour."

The device could also be used to study mating behaviour in some of New Zealand's most endangered birds, such as the kakapo.

"For an endangered population like that, you want to know who has mated with who," Professor Clout said.

DoC has helped design and manufacture the Mate ID. The Foundation of Research Science and Technology contributed $100,000 over two years.

The trial is in its third season and Dr Weihong is in the field getting ready for the possum mating season which begins next month. Fortunately, it lasts only until April. On average, the female possum is thought to produce one offspring a year.

In the early 1990s the possum population was put between 60 million and 70 million, and it was estimated they chewed through 20,000 tonnes of native bush every three nights.

They attack the eggs and young of some of New Zealand's most endangered birds and are carriers of bovine TB.

Efforts to control their spread through poisoning and trapping is estimated to cost between $60 million and $80 million a year.

nzherald.co.nz/environment