Australia's army has started shooting 6,000 kangaroos to thin their population on an army training ground near the capital, an official said Friday, outraging conservationists who have vowed to protest.

The killings are intended to protect endangered plants and insects that share the grassy habitat with the kangaroos. A much smaller slaughter of 400 kangaroos on another Defense Department site in Canberra last year was disrupted by protesters.

Civilian marksmen contracted by the department began shooting the kangaroos on Tuesday night at Defense's Majura Training Area, where an estimated 9,000 of the wild marsupials roam, Army Brig. Brian Dawson told reporters.

"The culling is intended to reduce the kangaroo population to sustainable levels," Dawson said, describing the action as that of a "responsible landowner."

The nighttime shooting is expected to continue intermittently until August. The training ground covers more than 7,400 acres and includes grenade and artillery firing ranges.

Bernard Brennan, president of Canberra's Animal Liberation conservation group, said protesters planned to descend on the area starting Friday night and many more would flock from around Australia next week. He could not predict how many.

"We're not going to sit back and let it happen," he said.

The kangaroo slaughter follows a recent government environmental report that the common eastern gray kangaroos are too numerous in Canberra's parkland and grassland, eating scarce native grass which is the habitat of endangered insects such as golden gun moths and perunga grasshoppers.

The kangaroo overpopulation is also threatening endangered reptiles, the grassland earless dragon and the striped legless lizard, the report said.

Kangaroos are slaughtered to control population throughout Australia, but government agencies have been reluctant to kill the beloved national symbol around Canberra in the past 20 years because of public outcry.