Islets in Danger

Forest and Bird, Issue 293, 1 August 1999, Page 20

Islets in Danger

Islets are vulnerable to weeds. Mike Lee found Papakohatu and Motukaha, both off Waiheke, to be very badly infested with rhamnus, Rhamnus alaternus, an aggressive environmental weed in the inner Hauraki Gulf. Here it also invades coastal forests, such as those on Rangitoto. Rhamnus is reducing species diversity on several islets, following an invasion route which could spread the weeds across the Gulf from Motuihe to Waiheke Island. Ecological values on all these islets have also been compromised to a greater or lesser degree probably by rodents. According to Mike, rodents are likely to have destroyed original lizard populations, disrupted petrel breeding, suppressed or eliminated larger invertebrates, inhibited the regeneration of plants, and predated bird nests. Nani and Passage Rock (1200 metres off Waiheke) were found to be rodentfree, but absence of lizards there possibly indicates earlier infestation, he says. Apart from invasive animal and weed pests, the immediate danger to the ecological values of these islets is disturbance of nesting birds by human intruders and their dogs during the summer breeding season.