The RSPCA is threatening legal action over a decision by the Defence Department to drastically reduce the kangaroo population at Puckapunyal military training base north of Melbourne.

The base - and the kangaroos living there - are enclosed by an electric fence. Officials have determined that the 36,000 kangaroos have an inadequate food supply and must be culled to prevent starvation. A minimum of 15,000 and as many as 30,000 'roos are to be killed by the end of August. More than 20,000 Eastern Greys were shot at the base last year.

Animal activists acknowledge the need to prevent suffering but are opposed to such massive reductions and point out that the fence is the real problem.