"We probably have deer every year, one or two, walking through the potatoes, which is not a worry," Mr Koenig said. "They are fallow deer. They are beautiful.

"This year, all of a sudden about six weeks ago before the rain, there was no green feed about. They must have got desperate."

At first he was mystified as to what had flattened his 40-metre long, heaped rows, until a neighbour watched the crop one night, and counted 30 deer from nearby bushland, digging out potatoes.

"I'm not too happy, I can tell you. I am prepared to share some of my stuff with the wildlife, but this is a significant part of our income," he said.

A solar-powered red flashing light is enough in summer to scare off wildlife. In winter, the deer ignore it. A neighbour shot at one deer, which is usually enough for these flighty animals to bound for cover in the timbered hills and Great Dividing Range that surround his crops.

But an hour after the shot was fired, they returned like brazen raiders.

Of the 12 potato varieties Mr Koenig sowed in November, the deer ate every one, except purple sapphire potatoes. Something released in their roots caused horehound, a noxious weed in southern Australia, to grow on top of them. Deer won't touch horehound.

Mr Koenig begins harvesting in February, mechanically raising 10 metres of earth a time. He leaves the remaining potatoes in the ground and continues to harvest through until August. Soil is ideal cold storage, as deer have discovered.

Mr Koenig and his wife Beatrice are resourceful on their 231-hectare farm. He carts away large quantities of dead carp from fishing competitions in Canberra to fertilise his crops. Mrs Koenig, a teacher, hosts classes from Merici College and Orana schools in Canberra.

The children connect quickly to the land, as have the wildlife. Not far from a sparkling lake, Mrs Koenig washes dirt from harvested potatoes, and the moment she turns her back, purple swamphen arrive. "They hop into the crate and start picking at the potatoes," she said.

Mr Koenig said: "Monaro wildlife are very grateful for our activities. They are not shy at all. It has been a tough winter and everyone is looking for a feed."

He said a neighbour years ago raised deer as part of a farming enterprise. "When the farm was sold, the new guys cut the fence and let them go."

An ACT Parks and Conservation spokesman said anecdotal reports from NSW landholders and government staff in the Michelago region indicated a large and growing feral deer population, predominantly fallow deer, although red deer were present in smaller numbers.

Under NSW legislation deer are classified as a "game animal", which put restrictions on deer control activities.

Invasive Animals Cooperative Research Centre says deer have increased 30 per cent across NSW from 2005 to 2009. Without a change in management approach, feral deer populations have the potential to occupy almost all of NSW.