The feral deer population caused huge headaches on the region's roads last season, in one case causing a 16-year-old motorbike rider to crash into a tree.

Three deer led police and a shooter on a chase through the streets of Fairy Meadow in August, with one of the animals being destroyed after being hit by a car on the Princes Hwy.

Homeowners living close to the escarpment also reported damage to their gardens.

In response to frustration expressed by the region's police and NRMA Insurance, who said the number of call outs was increasing annually, Wollongong City Council installed deer warning signs on several roads to alert unsuspecting motorists.

But without a concerted control program, the problems are expected to increase.

At the height of last year's season, the number of deer along the escarpment was estimated at 5000 by the NSW Game Council.

That number was expected to increase by 20 per cent by the end of the eight month gestation period, which ended last month.

This week, in line with the start of the mating season, the National Parks and Wildlife Service launched a 12-month culling campaign to reduce both the ecological and social impact.

For the next year, sections of the Illawarra Escarpment State Conservation Area will be closed from 8.30pm to 5.30am, Sunday night to Friday morning.

National Parks and Wildlife Service Illawarra area manager Joanne Edney said the main aim was to halt the damage caused by the deer through their grazing habits.

She said the deer had been introduced to the Royal National Park decades ago, and the long-term damage had resulted in changes to the vegetation, with plants being replaced by grass and other plant species being threatened.

"There are now places in the Illawarra where you go into rainforests and there is no longer an understorey," Ms Edney said.

"(The deer) also disturb the ground, they dig it up, particularly in rutting season.

"Because they are hard-hoofed animals, they cause more erosion just from the impact of their feet on the ground.

"Native animals have soft pads on their feet and don't do so much damage."

Ms Edney said the service began its deer control program in the Royal National Park but extended it to the Illawarra last year. "It has been recognised the deer have been moving south to become a big problem down here," she said.

Ms Edney assured the deer were culled in a humane fashion, the work carried out by marksmen from the Rural Lands Protection Board.

"They're the recognised experts," she said. "We want it to be humane so they have to be able to do it with one shot pretty much every time."