Staff at Central Park aviary in Boston found 30 birds missing and others killed by exhaustion and distress this morning.
The aviary had been broken into some time over Halloween night.
Around 30 birds are missing including budgerigars, parakeets, cockatiels and love birds worth in excess of £600.
Some of the birds had been donated by residents.
The crime has been reported to the police and park staff have secured the door and will look into what other measures can be taken to protect the aviary.
Other vandalism has occurred and it appears as though nearby trellis work was smashed down and a wooden post from that used as a battering ram to break into the wooden service door, including smashing down the trellis around the aviary.
CCTV footage is being reviewed to try to track down those response.
Portfolio holder for parks and open spaces at Boston Borough Council, Councillor Claire Rylott, said: “This is such a mindless, determined, deliberate and heartless act. The aviary is a lovely feature in Central Park, especially popular with families and children.
“The very fact that the aviary provides opportunity for anyone to view the birds makes it an easy target and very difficult to protect. The park is similarly difficult to protect from those who are determined and who will get in at any time. We continue to improve facilities in the park for all to enjoy and it is just so sad that anyone would want to spoil anything in a public park.”
Boston Borough Council wants to hear from anyone with information about this, or who is offered cage birds for sale, and people can contact police on 101 quoting crime number 51 of November 1.