The first trapping and culling of grey squirrels to take place in Aberdeen has got under way.
The invading grey has long caused problems for red squirrels
BBC Scotland can reveal traps have already started to be laid and the cull could last a month or even longer.
Animal protection group Advocates for Animals said the move - designed to protect the native red squirrel - was inhumane and would not work.
But Aberdeen City Council insisted the advance of the greys had to be stopped before it spreads to Aberdeenshire.
The cull is taking place in the city's Hazelhead woods where an experienced gamekeeper hopes to trap dozens of greys over the next few weeks.
The council said the animals would then be dispatched humanely with a quick blow to the head.
The north east is a stronghold for the red squirrel but they are still vastly outnumbered by the greys.
Countryside ranger Ian Talboys told BBC Scotland: "We're not looking at getting rid of all grey squirrels in the city, it's just to try to stop ones spreading out from the edge of the city into Aberdeenshire, where there are still good populations of reds and not many greys."
Grey squirrels compete for food with reds and also spread a disease which affects reds.
Ross Minett, of Advocates for Animals, called for environmental and habitat measures to help control populations.
He said: "We don't believe the culling of grey squirrels is humane and we don't really believe that it is going to be effective in the long-term to conserve red squirrels."
Aberdeen City Council said it was carrying out programmes such as replanting of habitats but it could not stand by and let red squirrels become extinct.