rat

Predation by introduced mammals is considered a primary threat to New Zealand’s native frog populations. Rats are known predators of the terrestrial Archey’s frog (Leiopelma archeyi), New Zealand’s smallest Leiopelmatid frog. During a 12 year study in Whareorino Conservation Area, we investigated effects of sustained rat control on survival, number of independent juveniles per adult, and abundance of Archey’s frog. Frogs were monitored following a capture-recapture robust design at four grids, split between a 300-ha ‘nontreatment’ area and a 300-ha rat control ‘treatment’ area.

The endemic fauna of New Zealand evolved in the absence of mammalian predators and their introduction has been devastating. Large-scale aerial applications of cereal baits containing sodium fluoroacetate (1080) are routinely used to control these pests. During one such operation in the Blue Mountains, West Otago, trail cameras were used to monitor the impact of the application on mammalian predators.

Invasive rodents pose one of the biggest threats to island ecosystems globally. Reliable methods for detecting and monitoring rodent presence are essential for the effective conservation management of islands, but many detection devices fail to attract rodents when natural resources are abundant. Using a toolbox of detection methods is therefore key to detecting rodents as individual rodents vary in their susceptibility to detection devices.

Recently introduced mammalian predators have had devastating consequences for biotas of archipelagos that were isolated from mammals over evolutionary time. However, understanding which antipredator mechanisms are lost through relaxed selection, and how they influence the ability of prey to respond to novel predatory threats, is limited. The varying effects on native lizard populations of the relatively recent and patchy history of mammalian introductions to New Zealand’s islands provide an opportunity to examine the consequences of relaxed selection.

Invasive rats can be capable swimmers, able to cross substantial water channels of hundreds of metres to colonise islands. This dispersal capability puts at risk islands close enough to infested areas for rats to reach unassisted. When reinvasion rates are high, biosecurity surveillance on islands might be supported by source population control to prevent re-establishment. However, biosecurity surveillance can only detect reinvading rats when they arrive and the source of reinvading rats might remain unknown.

Big South Cape Island (Taukihepa) is a 1040 ha island, 1.5 km from the southwest coast of Stewart Island/Rakiura, New Zealand. This island was rat-free until the incursion of ship rats (Rattus rattus) in, or shortly before, 1963, suspected to have been accidentally introduced via local fishing boats that moored at the island with ropes to the shore, and were used to transport the mutton birders to the island.

New Zealand’s offshore and outlying islands have long been a focus of conservation biology as sites