Last week, a swan and her three cygnets were killed near Eisey Footbridge in Wiltshire by teenagers armed with catapults.
The news was posted on a Facebook community page, The Only Way is Cricklade, on June 13 and was shared more than 1,700 times.
The post said: 'We have had some awful reports of teenagers with catapults attacking swans.
'One witness advised us that they killed three cygnets and a mother swan last night. They may have killed others as well.
'This is awful news. A cash reward has been offered for information that leads to a conviction.'
Hundreds of people commented on the Facebook page, describing the incident as 'heartbreaking' and 'sickening'.
Victoria Keville said: 'In these sad times it is such a joy to see these beautiful birds with their young.
'This is a criminal offence and the law needs to come down on those responsible. This is not acceptable – it's murder.'