Tiritiri Matangi – Kōkako – the grey ghost on Tiritiri

It’s almost 30 years since the first three kōkako, a female called Cloudsley Shovell and two males called Te Koha Waiata and Max, were released on Tiritiri Matangi in August 1997. They were followed a year later by four brothers of Te Koha Waiata: Te Toa, Te Karanga, Te Hari and Te Karere. Eleven more birds were brought to the island between 2007 and 2010. 

Since then, the population has grown remarkably, which has enabled 54 birds to be moved to other sites to assist in establishing recovering populations. Despite these departures, there are now around 99 kōkako on Tiritiri Matangi. 

Equally remarkable is the amount of work, largely by volunteers, that has gone into monitoring this population over the years. Every breeding season, which begins around October, they aim to locate and identify all the breeding pairs, find their nests, monitor the progress of their chicks and give them their coloured leg bands before they leave the nest. 

As a result of this effort, we know the family histories of all but a few of the 218 kōkako hatched on the Island since 1998, and have produced a unique data set for analysing their relationships and many other aspects of their lives.

One important issue for investigation is the impact of inbreeding (breeding between relatives) on ‘reproductive fitness’, which includes things like survival to breeding age, ability to find a breeding territory and a mate, the number of viable eggs and chicks produced, and whether those chicks survive to breed. The kōkako population on Tiritiri Matangi is descended from a small number of individuals, some of whom were closely related to each other. We know from studies on other species that these conditions can cause a decline in reproductive fitness. Some animal and plant populations are resilient enough to survive these impacts if they are not too severe, others are not and will decline to extinction.

The island’s current kōkako population still includes some breeding pairs in which the male and female are totally unrelated to each other, but most partnerships are between relatives – brother and sister, uncle and niece, aunt and nephew, cousins, and many other combinations, some with connections going back generations. Analysis of the data collected over nearly 30 years will help to determine the expectations for the Island’s population and whether interventions, such as bringing in new unrelated birds, might help. It will also be useful for the management of other kōkako populations around the country, some of which also have uncertain futures.