The government said on Friday that multiple nature reserves would be closed in the evenings from Monday, May 16, while staff moved to control the population of eastern grey kangaroos.

The cull was necessary to protect biodiversity and minimise impacts on other flora and fauna in critical grassland and woodland, director of parks and conservation Daniel Iglesias said.

But animal activists say they have no plans to hold back their efforts to stop the culls and scare off kangaroos, even as some face penalties and fines in court.

Carolyn Drew, of Animal Liberation ACT, said protesters had not been deterred by the government's recent attempts to pursue them in court.

"We've found the opposite," said Ms Drew, whose own case is coming up.

"What it's doing is, as people are reading up on the cases and seeing the government take a hammer to a pea, people are actually reacting to that and saying, hang on a minute, not only what you're doing to the kangaroo, but what you're doing to the people is unjust."

Christiaan Klootwijk, who blew a whistle near the site of a kangaroo cull, is serving a six-month good behaviour order after a court found him guilty in April of hindering the shooting operation.

But the activists remain optimistic about the effect their protests have on culls. "Last year we were pretty successful and the year before, we're getting better as we go," said Ms Drew.

She said that, as of Monday night, people would be out at the reserves, "sitting, listening, waiting, observing" for signs of a cull.

Robyn Soxsmith, of the Animal Protectors Alliance, was shocked and angered by news of the cull. "It's made us more determined to get out there and stop them from shooting these beautiful and peaceful animals."

Ms Soxsmith, who was out at a reserve on Monday, said the group were now developing protest strategies for the coming weeks.

The government has warned the public that fines apply for vandalising reserve infrastructure or entering closed reserves.

Sites slated for culling will be closed in the evenings from Monday, May 16, and reopen from August 1 at the latest.

Goorooyarroo Nature Reserve, Gungaderra Nature Reserve, Kama Nature Reserve and Mulligans Flat Woodland Sanctuary will be closed between 3pm and 7am each day.

Isaacs Ridge Nature Reserve, Mount Majura Nature Reserve, Mount Mugga Mugga Nature Reserve, Mount Painter Nature Reserve, Mulanggari Nature Reserve and the Pinnacle Nature Reserve will be closed from 5pm to 7am.