Pigeons, sparrows and gulls are dying at the hands of a mystery poisoner in the Auckland central business district.
People were distressed at finding birds that appeared to be stupefied but were slowly dying, said SPCA chief executive Bob Kerridge.
He said the suspected poison, alphachloralose, was a hypnotic that anaesthetised thebrain, stupefying the birds and eventually lowering their body temperature to the point of death.
The poison was indiscriminate in its target, he said, and was passed on to animals eating bird bodies, such as cats, dogs or other birds. He called for the poison to be withdrawn from sale to the public.
Efforts to trace the poisoner had failed but the SPCA believed it was either an "individual or a body corporate" trying to reduce the number of birds.
An Auckland City Council spokesman said last night that the council was not poisoning birds.
Council inquiries had failed to find who was laying the poison.
A city pest control contractor, Ray Butler, said he doubted it was the work of a professional. His firm, Fumapest, would not use the poison in public places.
"It's shocking for people to see a bird dying from it and can cause hazards such as birds crashing into vehicles."
Mr Butler said he believed the health authorities should not leave it to owners of restaurants and cafes to keep birds out of eating areas.
Professional pest controllers used safe methods such as trapping the dominant bird in the flock.
