Speaker Trevor Mallard has laid a complaint with the police over several dead birds used in a protest that were "almost certainly" bludgeoned to death.

The rare native birds placed on Parliament's steps during an anti-1080 protest were "almost certainly" bludgeoned to death, the Speaker says.

He has referred the matter to police.

The birds were definitely killed by blunt force trauma, and Massey University is now performing post-mortems on them to ascertain exactly whether or not they were bludgeoned.

Henry Cooke/Stuff The dead birds left on the steps of Parliament.

About a dozen birds were placed on Parliament's steps, including five native birds who have protected status, meaning it is illegal to kill or possess them.

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"The expert advice is that the birds were almost certainly bludgeoned to death," Speaker Trevor Mallard said.

The native birds were two kereru, two weka, and a Red-Billed gull.

The protest also involved throwing likely-fake 1080 pellets through the grates of the main doors into Parliament.

Video evidence would be provided to police or the courts of the incident but not to the public.

Mallard said he believed strongly in the right to protest but "they've got to stay within the bounds of the law."

"As a protected species under the Wildlife Act 1953 it is an offence to kill any absolutely or partially protected wildlife. It is also an offence to buy, sell or otherwise dispose of, or have in his or her possession any absolutely protected or partially protected wildlife. Individual persons are liable for an imprisonment term not exceeding 2 years or a fine not exceeding $100,000, or both."

He found it "particularly regrettable" that children were involved in the protest.

Anti-1080 protesters marched on Parliament in their hundreds on Saturday calling for an end to the use of the pesticide.

It was part of a nationwide series of protests attended by thousands.

Some of the protesters at Parliament wore skull and crossbones capes, chemical hazard suits and masks while others dressed in black with white crosses to symbolise the loss of the wildlife they say was killed by the poison.

A small number have camped out on Parliament's front lawn since then, writing messages in chalk on the border of Parliament's grounds.

It is not clear which group organised the placing of the birds, but comments online denied the birds were "bludgeoned", suggesting some were roadkill and some were picked up from a 1080 drop zone.

The Department of Conservation, Federated Farmers, and Forest and Bird all support the use of 1080 but several groups have been outspoken in calling for it to be banned claiming it kills native animals and birds.

Supporters say predator pest numbers are so high that without serious action some native forests would be seriously damaged.

The independent Parliamentary Commissioner for the Environment has found that 1080 is the best option for protecting New Zealand's wildlife.