The ACT Government closed off eight parks on Saturday night to allow a small number of marksmen to begin shooting the roos.

But the Department of Territory and Municipal Services will not reveal precisely when or where the culls will take place, saying it will comment on the operation only when it is finished.

The department has closed grassland and woodland areas inside and adjacent to Canberra Nature Park sites across the ACT until the end of July.

It warns trespassers they face fines of up to $5500 if they enter the parks.

The Government plans to kill up to 1890 eastern grey kangaroos, saying there are too many and their grazing threatens a number of endangered plant and animal species.

But Australian Society for Kangaroos' coordinator Nikki Sutterby denied yesterday there was any scientific evidence which suggested the ''kangaroos compete with any threatened species or damage grasslands''.

''Kangaroos are actually a natural and important part of the Australian environment and they have been in harmony with it for about 16 million years.''

She also said the target of 1890 kangaroos ''dramatically underestimated the real toll'', as many of the female roos would have dependent joeys.

''The joeys are clubbed to death or decapitated. It's absolutely brutal; they don't even spare a bullet ... A lot of joeys will be orphaned, too, because while they're still dependent they won't necessarily be in the pouch when their mums are shot.''

The society had members watching the culling sites who would act to stop the killing, but Ms Sutterby would not specify what they planned to do.

A departmental spokesman said the Government would issue a statement after the cull.

The spokesman also said, ''Any joeys that are killed will be killed in accordance with the code of practice, which has been endorsed by the RSPCA.''

For more on this story, see the print edition of today's Canberra Times.