DoC ranger Adrian Walker urged people to keep their pets out of Waitangi Forest, which had the highest kiwi density of any plantation forest in the country.
The birds were, however, vulnerable to dogs being walked in the forest or allowed to wander.
The forest had been the site of major predation events in the past but kiwi numbers had bounced back. The 2200ha Waitangi State Forest and the adjoining 570ha Waitangi Endowment Forest were a model of how plantation forestry and kiwi could coexist, Mr Walker said.
It was not known if the dog was being walked in the forest or had wandered in from a nearby property.
On September 1, an adult male kiwi was attacked by a dog as it was being walked along a road in Kaeo. The bird was still alive when it was taken to the DoC office in Kerikeri but its injuries were so severe it had to be put down.
If you have information about the Waitangi Forest kiwi death, or you see a dog in the forest, call DoC on (09) 407 0300; Northland Forest Managers on (09) 407 7115, or after hours the DoC hotline 0800 DOC HOT.