A peacock and 24 banty hens have been battered to death at an aviary in a municipal park in Bangor, County Down.
The dead birds were removed from view by wardens
A wire fence around a pen in Ward Park was cut and the birds were attacked with a blunt instrument. A knife was also found at the scene.
The USPCA has offered a £1,000 reward to anyone coming forward with information about the attack on the birds.
North Down UUP councillor Diana Peacocke said the slaughter of the birds was "beyond belief".
'Despicable and dreadful'
She said: "I find this latest attack of vandalism, in the form of a sustained attack, extremely deplorable and particularly low.
"To actually break in and attack defenceless birds in the highly-regarded Ward Park aviaries is beyond belief."
She said the birds had died as a direct result of "this despicable and dreadful action".
Ian Beaney of North Down Council, which runs the park, said they did not like to keep the birds caged or restricted.
He said: "The birds that are out and walking about, in 20 years I am not aware of an incident such as this in the park."
'Act of cruelty'
"From an aviary point of view, mainly it is one full-time member of staff who looks after that and he has pride in the work he does.
"He was distinctly distressed this morning when he came in to witness this."
DUP councillor Alex Easton said: "This is the worst act of cruelty that I have ever seen against defenceless animals and birds.
"It is just completely horrific. No words can describe the scenes."