Any crimes witnessed involving wild birds, including swans, should be reported to the Wildlife Crime officer at your county police station. It is worth noting that at this time of year Swan family groups split up and go their own way, which may give the appearance that birds have disappeared. It is also a sad fact that both adult and juvenile swans, despite their size are predated by animals such as foxes.
Luckily for me, my local Mute Swan family is still together. I'm about to create a thread featuring them having a bathing session yesterday morning. They really are spectacular!
Unicum arbustum haud alit duos erithacos
(One bush does not shelter two Robins)
Zenodotus (3rd Century B.C.)