At least 14 weka have been killed in a dog attack at the Mansion House historic reserve on Kawau Island, in the Hauraki Gulf north of Auckland.
The Department of Conservation is investigating the attack on the birds, which it describes as a serious threat to the weka population.
Two roaming dogs found at the scene have since been returned to their owner.
Biodiversity manager Rory Renwick says dogs can kill a large number of weka in a short time, and the latest attack shows the devastating impact pets can have on native animals.
He says the birds in the reserve form two-thirds of the North Island weka population.
Mr Renwick says people should not take pets with them when visting island reserves.
He says a dog found to have harmed protected wildlife can be impounded or destroyed, and the owner could face a fine of up to $10,000 and 12 months in prison.