Predators can indirectly structure local plant communities by altering the diversity and behaviour of herbivores. These ‘trophic cascades’ can be seriously disrupted by the local extinction of top predators. They can also be restored by the subsequent re-introduction of top predators by conservationists. Here, we investigated trophic cascades involving kākā, puriri moths and their host trees. New Zealand kākā (Nestor meridionalis, Nestoridae) are large parrots that were extirpated from most of its range in the 20th century.
The prevalence of infestation of the skulls of stoats with the parasitic nematode Skrjabingylus nasicola was previously described in a national survey by King and Moody (1982). Since then, more samples from Craigieburn Forest Park and from the Eglinton Valley, Fiordland, have been collected, and a method of determining the actual ages of adult stoats has been developed. The extended samples are here examined for a relationship between infestation and age, which could not previously be tested. Prevalence generally increases with age, significantly so at Craigieburn.