In the “Southern Islands Biodiversity Action Plan”
Cat control in dotterel breeding areas will continue according to the Dotterel Recovery Group recommendations. Any new cat control areas for protection of dotterels, will take into consideration other pest control work planned for the Management Units. New cat control areas have been identified in conjunction with the possum control areas. The Yellow-Eyed Penguin Trust should also be consulted in regard to protection at key breeding sites. Cat control should always be done in conjunction with rat and possum control.
Feral cats (Felis catus) on Stewart Island / Rakiura were introduced from Europe. Early European settlers brought cats to New Zealand from 1769 onwards, as a control agent on rat infested ships. However, it may have taken around fifty years for a feral population to become established on the mainland (King 1990). Ships have visited Stewart Island / Rakiura since 1804, and in 1909 Cockayne reported cats to be “common”.
There is no evidence that they grow any larger than cats which live in a domestic setting (Harper 2002). Male cats on Stewart Island / Rakiura average 3.4 kg and females 2.6 kg. Cats are efficient predators, and hunt diurnally and nocturnally. They will live in almost all habitats. Their diet is composed mainly of rats, although birds, reptiles and invertebrates together compose a significant proportion (Karl and Best 1984, and Harper 2002). Stewart Island’s feral cat population has been blamed for the near extinction of kakapo (Strigops habroptilus), and southern New Zealand dotterel. Indigenous reptiles, yellow-eyed penguins (hoiho; Megadyptes antipodes), little blue penguins (korora; Eudyptula minor), kaka (Nestor meridionalis meridionalis) and young kiwi (Apteryx australis) are other species that are susceptible to cat predation.
Grant Harper (from the University of Otago), has carried out a study of the cats that live in the vicinity of New Zealand dotterel breeding grounds at Mount Rakeahua and Table Hill. The feral cats he examined were lean and apparently restricted in numbers by seasonal lows in rat abundance. However, it can be noted that hunters claim to have killed around 60 cats each year between 1985 and 1991 (based on hunting returns) with no appreciable impact in the population.
Cats are absent from Ulva and Bench Islands. During the early 1990s, cat control was carried out around Long Harry to protect the yellow-eyed penguins that breed there. Existing control is at New Zealand dotterel breeding grounds on Table Hill, Spot Height 511, Spot Height 464, Mount Rakeahua, and Rocky Mountain. Fish meal polymer baits containing 1080 pesticide are placed in bait stations. The bait stations are arranged at 50m intervals in a cordon around breeding areas, and also contain bromadiolone rat baits (DOC 2000a). For more detail see Avis (1996) and Dobbins (2001).
Control of cats is to be undertaken within Management Units (Hall 2000) and be aimed at the highest biodiversity value areas on the island (Hall and Beaven 2001). Cats’ main impact is as a predator. Control work should aim to establish safe breeding areas (core breeding areas) for species that are vulnerable to cat predation. These areas should be within possum control areas, allowing integrated conservation management. Cat work will usually be done in conjunction with possum control and always in association with rat control. But, there may still be a requirement for specific cat protection for certain species, e.g. New Zealand dotterels and yellow-eyed penguins.
- Control is prioritised to critically vulnerable breeding areas, within areas of greatest biodiversity value, enabling vulnerable prey species to increase in numbers.
- At least one Management Unit within each District has control within it to a level that allows species vulnerable to cat predation to increase in numbers.
- Control in New Zealand dotterel breeding areas has enabled species recovery goals to be acheived.
Performance measures and targets
Performance will be measured by achievement of the following targets:
- New Zealand dotterel protection continued and extended to achieve a population of 250 birds by 2011 (species recovery goal).
- One new cat control area implemented by July 2004.
- At least two yellow-eyed penguin breeding colonies, have cat control implemented by July 2004.
Means of achievement
The purpose of the work programme is to improve ecosystem health, rather than cat control in itself. With cat control, a sustained treatment is required, often over large areas, since cats’ home ranges on Stewart Island / Rakiura can reach ten square kilometres (1 000 hectares; Harper 2002). Environment Southland is to be approached to work in conjunction with the department to reduce the effect of cat populations on private land.
Available options for control are: 1) status quo; 2) trapping; 3) further toxin options (ground or aerial application); or 4) a combination of these.
If nothing more is done to control cats, their impact on many native species will continue unabated. Dotterel protection is targeted to one habitat type, providing limited protection for several other vulnerable species such as Stewart Island fernbirds (matata; Bowdleria punctata stewartiana), Stewart Island robin (Petroica australis rakiura) and indigenous lizards. It provides little protection for penguin species, which are also vulnerable to cats. Long-term consequences are likely to be further loss of biodiversity values and possible extinctions. This option leaves a number of Districts without cat and rat control, and therefore habitat restoration goals un-achieved.
Trapping will need to comply with internal policy for ground bird areas (e.g. raised sets) and with the Animal Welfare Act as it applies to traps. Traps fall into two broad categories: kill and live capture (cages and soft jaw leg holds). The applicability of traps will be assessed on a case by case basis.
Toxins that are legally registered for use on cats are listed in Table 3.
Registered cat pesticides
Name: Diphacinone (Pestoff Ferret Paste)
Technique: Bait stations
Comments: Less potent than Brodifacoum; less persistent than Brodifacoum.
Name: Sodium Monofluoro-acetate (1080) (Pestoff Feral Cat Bait)
Form: Dried Meat Meal Pellets
Technique: Bait stations
Comments: Not cumulative or persistent in the environment although does persist in carcasses; is not well perceived (controversial); bait shyness can occur with sub-lethal doses.
The main technique associated with toxic baits for cats are bait stations. Ground based control work is labour intensive, but the intensity varies with other factors such as technique, accessibility and field life of the bait. Certain techniques and baits can result in a relatively cheap method of control, and can also reduce the likelihood of by-kill of other animals, e.g. birds. Toxins and trapping can be combined.
Figure 5: Proposed rat and cat control areas in Rakiura/Stewart Island