predators

In 2016, the New Zealand Government announced a policy to rid the country of key introduced predators (possums (Trichosurus vulpecula), ship rats (Rattus rattus), Norway rats (R. norvegicus) and mustelids (Mustela spp.)) by 2050. An interim goal under this policy is to remove all mammalian predators (the key species as well as mice (Mus musculus), kiore (R. exulans), cats (Felis catus), pigs (Sus scrofa) and hedgehogs (Erinaceus europaeus)) from island nature reserves by 2025.

Ship rats (Rattus rattus) were removed from sites on Pearl Island, southern Stewart Island, in 2004 and 2005, to test whether they excluded Pacific rats (R. exulans) or Norway rats (R. norvegicus) or both from podocarp-broadleaf forest. As predators can influence habitat use in rodents, Pearl Island was selected because no mammalian predators of rodents are present. Rats were trapped in two other habitats to clarify rat distribution on the island and to obtain samples for stable isotope investigation of food partitioning within habitats.

We recorded trap site characteristics and captures during a trapping programme designed to protect breeding and released black stilts (kaki, Himantopus novaezelandiae) from predation, in order to learn about trap site features that might improve the efficacy of future predator trapping management. Captures were made at 1629 leg-hold traps opened over 71 333 trap nights between 1998 and 2000, at six locations in the Upper Waitaki Basin, New Zealand. Twelve trap site variables were recorded.

The sex ratio of the kaka population inhabiting the Waihaha Ecological Area, Pureora Forest Park was estimated between late October 1994 and January 1995. The observed sex ratio estimate was three males to one female compared to a capture rate (using mist nets) of six to one in the same area between January and June 1994. Females appeared to be less susceptible to capture than males. The skewed sex ratio toward male kaka was significant and suggests that female kaka suffer higher mortality (probably due to predation at the nest) than males.

The distribution and abundance of lizards relative to habitat structure were studied at Pukerua Bay, Wellington between December 1982 and March 1988 in order to identify options for management of the habitat of the five species of lizards present. One species, Whitaker's skink (Cyclodina whitakeri), is a threatened species with only one known mainland population. Pitfall traps were set for 23 667 trap-days and yielded 2897 lizard captures. Highest capture rate was for common skinks (Oligosoma nigriplantare polychroma) and lowest rate was for C. whitakeri.

The control of introduced mammalian predators has become a standard response to protecting the viability of threatened wildlife species on oceanic islands. However, examples of successful outcomes of integrated pest control in forests are few. We investigated the efficacy of a pest control programme in the Landsborough Valley, New Zealand, during 1998–2009, which used continuous trapping to control mustelids and pulsed aerial application of the toxin 1080 to control rats (Rattus spp.) and brushtail possums (Trichosurus vulpecula).

Black-fronted tern (Chlidonias albostriatus) breeding populations on braided rivers in the South Island, New Zealand, are assumed to be in decline as their habitat comes under increasing pressure from exotic pests, hydroelectric power development and water abstraction. We collated 326 index counts of black-fronted terns from 2313 km of surveys on 84 rivers throughout their breeding range to test this assumption. Black-fronted terns were observed on 73% (n = 61) of rivers surveyed, and the sum of the most recent counts was 8325 birds.

Biological invasions have significantly affected New Zealand’s native species and ecosystems. Most prominent are the effects of exotic mammals and plants, whereas few invertebrate invasions are known to have major effects on native ecosystems. Exceptions are the well-known cases of Vespula wasps in Nothofagus forest ecosystems and Eriococcus scale insects in Leptospermum shrublands. This limited impact is surprising because over 2000 exotic invertebrates have become established in New Zealand, among them many pests of exotic crop plants.