A flock of 60 pigeons were killed when arsonists set fire to an allotment.
Intruders are thought to have broken into sheds at the Brierton Lane allotments, in Hartlepool, and started the fire on Sunday evening.
Some of the birds were saved by two of the allotment holders who saw the blaze and managed to open one shed and release 20 pigeons, but the rest died.
The pigeons are all believed to be owned by the same man.
Station Officer Steve Waggot, of Hartlepool Fire Brigade, said: "Because of somebody's malicious actions a man's life's work has gone up in smoke.
"We believe this was deliberate ignition. There was a rescue made by two adjacent allotment holders. They rescued 20 pigeons.
"These two people, wearing T-shirts and jeans, managed to scale a barbed wire fence.
"Unfortunately there was nothing much they could do for the second pigeon loft."
Five cabins were destroyed in the fire.
Detective Sergeant Tony Green of Hartlepool Police said: "This was a callous attack which must have caused unnecessary suffering to the birds before they died.
"Anyone with information about the attack is asked to call us on (01642) 326326."
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