"Despite all the signs saying it's a kiwi zone and dogs have to be on a leash or are banned it's amazing the number of people with dogs up there."
Department of Conservation senior biodiversity ranger Nigel Miller described terriers as "little killing machines".
He said often dogs that wandered would go for possum or rats but they were able to escape and climb trees, kiwi could not and that's when dogs could become specialist kiwi killers.
"Uncontrolled dogs can also hunt in packs and in this case we have two dogs together. It only takes one dog to get a taste for kiwi and they can destroy a population if they are not caught," Miller said.
"The recently released kiwi population in Pukenui Forest are trying to establish themselves. Losing adult birds is a recipe for disaster."
Twelve adult kiwi, with transmitters attached, were released into the Pukenui Forest on March 17, and are being monitored for the next 12 months.
Pukenui-Western Hills Forest Trust chairman Max Hutchings said it was hard for dog owners not to know the area was a no dog zone as there were clear signs at every entry and exit point to the forest.
"If we lose more than four kiwi there is the potential we will have to take the rest out as that's part of the agreement we have with DoC. Dogs are the biggest killer of kiwi in Northland by a long way, and a lot of these dogs are pets that people don't control."
He encouraged anyone who saw dogs in the forest to gather as much information and alert the trust through their website or Facebook page.
