Little spotted kiwis are not only thriving on an island sanctuary near Auckland - they are breaking into the heavyweight division.
The latest five-yearly survey by Department of Conservation staff, completed last month, found Tiritiri Matangi's little spotted kiwi population has trebled in just under a decade.
But aneven bigger surprise was the size of the two biggest birds. A female tipped the scales at 2.04kg and a male at 1.54kg, the heaviest recorded.
"At this rate we'll have to start calling them medium spotted kiwi," said department science officer Rogan Colbourne.
The heaviest female found during the 1997 survey weighed just under 2kg.
The latest survey shows the little spotted kiwi population on the island is at least 50 birds and could be as high as 60.
Sixteen little spotted kiwi (Apteryx owenii) were transferred to Tiritiri Matangi Island in the Hauraki Gulf in 1993.
Two birds died shortly after release and a further six birds were transferred in 1995.
Mr Colbourne said the numbers had increased at every island at which the birds were introduced, but the fastest increase had probably been at Tiri.
Little spotted kiwi are extinct on mainland New Zealand but survive on carefully managed offshore islands. They are the smallest of the six types of kiwi, about the size of a bantam, and the most endangered.
Because of their size they cannot fend off predators as well as their bigger cousins, the great spotted kiwi and the North Island brown kiwi.
But they are thriving on Kapiti Island near Wellington where their numbers have reached about 1000.
Mr Colbourne said one of the reasons for the large birds found on Tiri was that the island was rat-free so little spotted kiwi did not have to compete with them for food.
Stoats remained the most dangerous predator for kiwi on the mainland.
