The Importance of Birds as Browsers, Pollinators and Seed Dispersers in New Zealand Forests

New Zealand's forest plants evolved in the absence of mammalian herbivores, but subject to the attentions of a variety of other animals. Insects are and probably were, the primary folivores, but birds may also have been important. Several extinct birds, notably moas (Dinornithidae), were herbivores, and speculation continues about their impact on the vegetation. Among existing forest birds, both kereru (Hemiphaga novaeseelandiae) and kokako (Callaeas cinerea) can significantly defoliate plants and may have had a greater impact in the past. Beneficial interactions of birds with forest plants include pollination and seed dispersal. Flower visitation by birds has already been reviewed, but the importance of frugivory and seed dispersal by birds has hitherto been given scant regard in New Zealand. About 70% of the woody plants in New Zealand forests have fruits suited for vertebrate dispersal and, of these, most are probably dispersed by birds. The recent extinction of several frugivorous forest birds (e.g., moas, piopio Turnagra capensis, huia Heterolocha acutirostris) and the decline of others (e.g., kokako) has reduced the number of potential seed dispersers, especially for large-fruited species, some of which now depend almost entirely on kereru for seed dispersal. A similar recent loss of potential seed dispersers has occurred throughout Polynesia, but consequent effects on patterns of forest regeneration are unknown.