Witnesses said they were aiming for the island where the swans had made a nest and three of the six eggs were left smashed.
Wildlife activists, who were monitoring the swans, said more eggs were lost in recent weeks, leaving just one surviving egg.
They added that the father swan was driven away from the nest due to stress two weeks ago and has not returned since.
The female swan has been harassed by moor hens, ducks and a dog since her unhatched eggs were first attacked.
The heartbroken activists sadly found the female swan dead in her nest earlier this week.
Activist Sam Woodrow said: 'There's not much I can say really.
'She probably died of a broken heart as she had a partner for life and he was driven away by stress.'
According to Swan Lifeline, it has been known for swans to die of a broken heart if they lose their partners, as swans generally mate for life.
Posting on Facebook, Michael Mason said: 'Her mate left her on her own and sadly I was informed this morning she was found slumped in her nest dead. I just feel like crying.