Misguided: Protest signs have been erected to deter a series of cat killings in Raglan which is having a disastrous effect on the native bird population.

The misguided logic of a Raglan cat killer is having disastrous and unintended consequences for a community's local birdlife, an ecologist says.

Residents in Raglan West, a tiny neighbourhood of around 20 houses, have had 16 cats go missing from the neighbourhood over the past year, according to Raglan veterinary clinic.

The disappearances are turning neighbours against each other and leading to suspicion, threats and intimidation. But the alleged killings are also having unintended consequences for the local bird population, one resident says.

Adrienne Livingston , a private ecological consultant and former ecology lecturer at Northland Polytechnic, is concerned about the number of half-eaten eggs and dead chicks she is finding strewn across her back yard.

''I am now observing the effect the marked absence of cats is having on this suburban ecosystem.''

The cat killers are known to be birdlife enthusiasts, she said, but instead of helping native birds, they are enabling the rodent population to rob bird nests unchecked.

She said cats were the apex predator in the immediate area, but their absence had allowed rats to flourish.

Landcare Research wildlife ecologist John Innes said it was possible the removal of cats in an urban area could have a net bad outcome for wildlife.

''Ship rats are the tree climbing rat that decimates most native birds in New Zealand and they're a major item of cat diet.''

The disappearances and possible damage to the local bird life have prompted a group of concerned residents to erect about 30 signs around Raglan. The signs, which have been placed in several places between Raglan West and Te Uku, have a cat and crossbone symbol and read: ''Stop Raglan cat killer.''

The group have also uploaded a video to YouTube warning Raglan residents of the danger their cats are in, and discussing some of the possible ecological consequences of cat eradication.

Livingston said she was only monitoring about four bird nests in her backyard, but evidence from the small sample size suggested ''total annihilation''.

In September, former and current residents of the neighbourhood sent Waikato Times copies of affidavits they wanted to use to urge a police prosecution.

But without hard evidence they have been told there was nothing authorities could do.

Raglan resident Andrew Lovrin, who was part of the group behind the signs, said he felt let down by the authorities, who had done nothing to bring the killers to justice.

He said he was aware of two disappearances in the last few months.

Nigel Kearins, who has been busy putting up the signs this week, said he knew who the culprits were and had informed police, but no action had been taken.