The mystery of the Montague Island 'mouse'

Pic: On the hunt ... Department of Environment officer Nicholas Carlile looks through a device which, it is hoped, will record identifying footprints of the mystery marsupial. Inset: Chief suspect ... sketches of a dusky antechinus. Photo: Rick Stevens

The mystery of the Montague Island 'mouse'

James Woodford
June 20, 2009

IT IS the mystery of the Montague Island "mouse" that shouldn't be there.

The 80-hectare nature reserve, nine kilometres off the NSW South Coast town of Narooma, has suffered a feral mouse plague that has lasted for about 130 years, since the lighthouse station was established.

Goats, rabbits and an impenetrable infestation of introduced kikuyu grass have also cursed the island's ecology. The last goat was shot in the late 1980s and for the past decade scientists and park managers have been determined to declare the island feral-free.

Two years ago a massive baiting program using poison-laced cereals distributed by helicopter simultaneously wiped out the entire rabbit and exotic mouse population.

The equivalent of thousands of nights worth of trapping and track analysis, without any sign of the pests, has made researchers confident the island is indeed free of mice.

But in recent months three staff have sighted at least three examples of a small, rat-sized mammal "shaped like a black tube, that doesn't hop, with a nondescript tail".

On one occasion two people saw the odd little beast while they were walking together.

Because of the scale of the baiting and the huge follow-up surveys for mice it cannot be a rodent, says seabird project officer with the Department of Environment and Climate Change, Nicholas Carlile. Yet not one single NSW offshore island has a native terrestrial mammal population, Mr Carlile says. That is, possibly, until now.

A search has begun this week to solve the mystery. According to Mr Carlile, the most likely theory, based on the descriptions of those who have seen it, is that the recently spotted mammal is a dusky antechinus.

"What I don't understand is how a native mammal has been out here since the constant human presence following 1881 and hasn't been seen," Mr Carlile says.

Unlike mice, rats and other species of antechinus, dusky antechinus would not readily stow away in gear brought onto the island. This means that it is possible the population has survived as an isolated colony for up to 10,000 years since sea level rise separated Montague from the mainland.

Dusky antechinus are also not cereal eaters and would not have taken the baits laid to kill mice and rabbits.

A trapping program began this week in an attempt to capture a live specimen so the creature can be identified. But because it is thought to be in such low numbers success may take many months.

Whatever it turns out to be, Mr Carlile is confident that Montague will have more surprises. A new population of storm petrels established itself on Brush Island off Ulladulla last year following a rat eradication in 2005.

Other spectacular ecological recoveries are under way following the removal of rabbits from Cabbage Tree Island off Port Stephens and the same is hoped for nearby Broughton Island with the removal of rats and rabbits later this year.

All of these feral pest eradications, though, are dress rehearsals for the most ambitious plan of all - the total eradication of rodents from Lord Howe Island in 2011. It is not just the environment that benefits, says Mr Carlile.

"One of the big things is the improvement of the amenity both for people who operate and work in these places and the tourists who pay to visit these sanctuaries," he says.

"They are no longer exposed to the diseases that mice carry or leave in their droppings and the historic fabric of buildings [like the lighthouse quarters on Montague] are more easily protected."

http://www.brisbanetimes.com.au/national/the-mystery-of-the-montague-island-mouse-20090619-cr8b.html