The Influence of Browsing by Introduced Mammals on the Decline of North Island Kokako
- Forest Research Institute, Private Bag, Rotorua, New Zealand
- Royal Forest and Bird Protection Society
- Ecology Division, DSIR, Private Bag, Lower Hutt, New Zealand.
- Present address: Zoology Department, University of Auckland, Private Bag, Auckland, New Zealand
The diet of the North Island kokako (Callaeas cinerea wilsoni) was studied in three central North Island habitats, Pureora, Mapara, and Rotoehu, for three years. Possum (Trichosurus vulpecula) diet was less intensively studied for part of the same time in Pureora and Mapara. A literature review was made of the diet of possum, red deer (Cervus elaphus), and feral goat (Capra hircus). There is considerable overlap between the diets of kokako and the three mammalian browsers; leaves and/or fruit of some species are eaten by all four, e.g. mahoe (Melicytus ramiflorus), fivefinger (Pseudopanax arboreus), lawyer (Rubus cissoides), pigeonwood (Hedycarya arborea), and raurekau (Coprosma australis). Possums, red deer, and goats have reduced the abundance of preferred kokako food plants in much of the remaining kokako habitat. The present distribution of kokako suggests that their decline has been caused not only by forest clearance and introduced predators, but also by impoverishment of habitat resulting from the introduction of browsing mammals.