Six swans are feared to have been stabbed and beheaded after their mutilated bodies were discovered in south London parks.
Patrols including local volunteers have been set up after the grisly finds in Thamesmead in the last month.
Two mute swans were found beheaded in Birchmere Park in November and another swan was also killed in Southmere Lake.
All wild mute swans in Britain are considered to be the property of the Crown and it is an offence to kill one.
Swans have statutory protection under the Wildlife and Countryside Act 1981 and anyone found guilty of trying to injure a wild bird, or kill or take it without a licence, can face up to six months in prison and/or a fine of up to £5,000.