A swan’s severed head was found next to its body by a road in Bletchley over the weekend.
The perpetrator deliberately chopped off the protected bird’s head on Stoke Road.
Police say the vicious attack is similar other swan deaths last year.
The severed heads of three swans were found close to the water at Mount Farm Lake by members of the Beacon Angling Club in April (pictured).
It is believed police are linking the crimes.
PC Andrew Hipkin, Wildlife and Crime Officer for Milton Keynes, said: “This is a particularly unpleasant crime and I am keen to trace those who are responsible for the death of this swan to prevent any further incidents.
“The mute swan is a protected bird and property of the Crown.
Killing a swan can result in a six-month jail sentence and/or a fine of up to £5,000.
Police are now appealing for information and witnesses to the attack.
Mr Hipkin added: “I am looking for any witnesses to this incident, especially those who use the Grand Union Canal in this part of Bletchley.”