Adoption is the legal transfer of all parental rights and responsibilities from a child's birth parents to the adoptive parents.
Prior to starting a search to locate birth parents an original pre-adoption certificate can be applied for. Details can be found on the Department of Internal Affairs website:

Once the pre-adoption certificate has been obtained these other avenues are available:

The original pre-adoptive birth certificate will usually show the birth mother's full name, age, marital status, her maiden name (if married), and her place of birth. The birth records on microfilm in the New Zealand Room at the Tauranga City Library can be searched to find the folio number of the mother's birth. You can then obtain a copy of the birth mother's birth certificate. This will provide details of her birth parent(s) and if she has any older siblings.

Then search electoral rolls from the date of the birth of the birth mother and also for other family members (parents and siblings). Tauranga City Libraries holds every New Zealand electoral roll from 1854 to the present. It may be easier to trace the birth mother through her parents and siblings, especially if she was very young at the time of the child's birth. For instance, her parents may have resided in the same street in the same town until their deaths.

Death certificates of either parent will show the date of death but also how many surviving children (if any), their sex and ages. Death notice's in the local newspaper will give names of family members and possibly the married name of the birth mother and where she resided at the time of the death.

Christchurch City Libraries -
Ministry for Vulnerable Children Oranga Tamariki -
Family Court -
Youth Law -

New Zealand Room - FAQ's

04/18 LB