Auckland Island, the fifth largest island in New Zealand, is the only island in New Zealand’s subantarctic region where introduced mammalian pests remain (pigs, Sus scrofa; mice, Mus musculus; cats, Felis catus). The island has unique biodiversity and is a key site for progressing New Zealand’s goal to be free of several introduced predators by 2050. Recent island eradication successes have rekindled interest in eradicating pests from Auckland Island, and for the first time considering all three pests in one project.
As a major threat to New Zealand’s biodiversity, feral cats (Felis catus) are the subject of planned eradications on a number of offshore islands, including Rakiura Stewart Island. We used camera traps to estimate population density of feral cats on the north-east coast of Rakiura, and to investigate their movement behaviour and detection probability. We also used camera footage to compare the consumption of two types of non-toxic sausage baits (chicken and rabbit) with a view to future use of toxic baits.
In order to conserve important biodiversity values, eradication of feral cats (Felis catus) is planned on Auckland Island in the New Zealand subantarctic region. This eradication will require detailed knowledge of the abundance, distribution, movement behaviour and detection probability of cats on the island. We investigated these parameters on a peninsula at the northern end of the island using live trapping, camera trapping, and scat searches with and without detection dogs. Here, we compare the results of these methods, and discuss their utility for the planned eradication.
Domestic cats (Felis catus) in Halfmoon Bay, Stewart Island/Rakiura, were tracked to assess the potential for incursions into native forest around the township, and into Rakiura National Park c. 5 km away. During February and April 2005, 15 and 4 radio-collared cats were tracked, respectively. During a six-month period, cat-owners logged prey brought home by 11 cats. Cats were at home >90% of the time. Of the six cats that left home, movements were small: home range was between 0.05 and 16.6 ha (100% minimum convex polygon).
Feral cats (Felis catus) are predators and competitors of native species on many islands and are therefore the target of control efforts. Cat eradication has been achieved on 83 islands worldwide. Six of these successes have been from large islands (over 2000 ha) and have reported sufficient data to examine how the eradication was achieved through combinations of aerial and ground-based poison baiting, fumigation in rabbit burrows used by cats, cage and leghold trapping, day and night shooting, and hunting with dogs.
A single five night pulse of sodium monofluroacetate (0.15% 1080) applied in bait stations at two different spacing intervals, 100 and 200 m, along forestry roads in New Zealand beech forest, killed all four of the resident radio-tagged stoats (Mustela erminea) and all three of the resident radio- tagged wild house cats (Felis catus) by secondary poisoning. Gut contents of predators indicated that house mice (Mus musculus), ship rats (Rattus rattus) and bushtail possums (Trichosurus vulpecula) were important sources of the toxin.
Aerial poisoning using Talon(R) 7-20 baits (active ingredient 20 ppm brodifacoum) was carried out on Motuihe Island, Hauraki Gulf, during the winter of 1997. The operation aimed to eradicate Norway rats (Rattus norvegicus) and house mice (iMus musculus) and to reduce rabbit (Oryctolagus cuniculus) numbers significantly. We studied the diet of feral house cats (Felis earns) before the operation, then monitored the impact of the operation on them to determine whether secondary brodifacoum poisoning caused a reduction in their numbers.
We monitored the behaviour of 62 radio-collared ferrets and 25 radio-collared cats in dry, tussock grassland habitat in New Zealand's South Island. The total home range of adult male ferrets (102 ± 58 ha, mean ± 1 s.d.) was marginally greater than that of females (76 ± 48 ha), and averaged 90 ± 55 ha. Male ferret core ranges (27 ± 15 ha) were larger than those of females (16 ± 8 ha). Adult cat home ranges were similar between sexes, and were larger and more variable than those of ferrets (225 ± 209 ha). Core range size of cats was similar between sexes and averaged 54 ± 24 ha.
Feral cats became established on Raoul Island some time between 1836 and 1872; the prey available to them included a great variety of nesting seabirds, few of which are present now, landbirds and kiore (Rattus exulans). Norway rats reached the island in 1921, providing additional prey for cats, but also another potential predator of seabirds. The diet of cats is described from guts and scats collected between 1972 and 1980. Rats are the main food, with land birds second in importance, and seabirds are now a minor item.
Efficient detection techniques will confirm the presence of a species at a site where the species exists, and are essential for effective population monitoring and for assessing the outcome of management programmes. However, detection techniques vary in their ability to detect different species. A wide range of mammalian predator species, most introduced into New Zealand since the late 18th century, have had a detrimental impact on the native flora and fauna.