The city initially impounded the dogs, however they have been returned to the owners pending a court hearing.

A city spokesperson said the dogs must be kept under effective control at all times until the matter is dealt with. The swans were among eight that were in the process of being rescued after being abandoned by their parents, however the three were killed before all could be saved.

Beverley Sykes, who rescues abandoned cygnets and rehabilitates them on her Wonnerup property before releasing them on to wetlands said she had been told about the cygnets.

“I had gone out at 3pm to take a look at a group of eight and decided to go back the next day to see if we could pick them up,” she said.

“However, a resident rang at around 6.30 to say three had been killed. When we went to get the others a ranger managed to track the dogs back to their home and apparently apprehended them.

“The remaining five cygnets were rescued and are now floating on fresh water at our place.”

Beverley, who tends to scores of cygnets each year, said she was disappointed with what had happened.

“We’re disappointed with people who do not control their dogs at all times. It’s particularly concerning when we have young water birds around at this time of the year,” she said. “They are the ones targeted and can’t get away from them because they can’t fly. It’s the owners’ responsibility to know where their dogs are and ensure they are controlled at all times.”