Police are investigating after five swans were shot in the head with an air rifle, killing one.
A nesting swan was shot while tending to its unhatched eggs in Thatcham, Berkshire last week, marking the fifth such attack on waterfowl in the area in 10 days.
The eggs were taken to a support centre and the mother is expected to make a full recovery.
“She was sat on a nest and they shot her in the head – we got a call to say she had blood all over her head,” said Wendy Hermon, from the Swan Support charity.
Ms Hermon said the swan had had an operation to remove an 8mm ball fired from an air weapon.
She added: “I think it’s sick, sick people who have nothing else better to do. How can someone shoot a defenceless swan sat on a nest?”
The Queen’s swan marker has been notified following the spate of attacks and described them as “mindless cruelty”.
”I am shocked and disgusted to learn of the shooting of a female swan who was sitting on a nest of four eggs,” said David Barber MVO, who oversees the care of swans on the Thames and elsewhere.
“This type of mindless cruelty is totally unacceptable and unnecessary and I sincerely hope the perpetrator of this abhorrent act will be pursued and punished accordingly.”
Mr Barber added that the nesting female had suffered a “life-threatening” injury and could still die.
Anyone with information should call Thames Valley Police on 101 quoting reference 43200122152, or Crimestoppers anonymously on 0800 555 111.
Under the Wildlife and Countryside Act 1981 anyone who harms a wild swan could be jailed for up to six months.
The Queen has the right to own any unmarked swan in open waters, although this right is usually only exercised on certain stretches of the Thames.
Additional reporting by agencies