Wellington's Zealandia has tagged its 400th kaka since the native parrot was introduced to the sanctuary in 2002.
Volunteers Judy and Linton Miller, of Ngaio, celebrated the milestone while placing unique identification bands on four chicks from the same nest yesterday.
The process involves taking various measurements, then microchipping them for monitoring.
Zealandia's Lauren Schaer said the bands could keep track of how long each bird lived, where they bred, and breeding partners.
It is understood there are now 200 to 250 kaka in the valley, which provides a predator-free, safe environment for breeding.
"Locally, they were very rare in Wellington. While the sanctuary is here, they have crucial support."