A swan was shot in the neck and killed at a lake on a Corby estate.
The bird, one of a pair which had five cygnets, was shot at the lake on the Oakley Vale estate between midday on Tuesday, October 8, and 7.45am on Wednesday, October 9.
RSPCA inspector Clint Davies is appealing for witnesses to the incident to come forward.
He said: “It had a hole in its neck which looked like it had been caused by a pellet from an air rifle. It had gone in one side and straight out the other.
“Not only was this act illegal, it was cruel. I am hoping anyone who saw anything, or knows anything will come forward with information.
“Someone may have seen someone walking through the estate with an air rifle. It’s quite an open area.
“The remaining swan, the female, and the cygnets appear to be alright but this will have caused them unnecessary stress. It was such a stupid act.”
It is believed the air pistol pellet, between 1.7mm and 2.2mm in size, was shot at close range.
Anyone who has information can pass it on to the RSPCA by calling 0300 1234 999 or to the police on 101.