Should Felix take the rap?

Forest and Bird, Issue 280, 1 May 1996, Page 34

Should Felix

take the rap?

KEN CATT

Ian Close

We all know that cats will hunt native wildlife. But are they the major conservation problem in mainland areas

we have been led to believe?

looks at some of

the ecological dilemmas of cat control.

y | | ERAL CATS kill New Zealand dotterel," reads the headline. But the fact is that the role of cats as predators of native birds and other animals in most New Zealand habitats is not well understood and little

is Known about what would happen If cats were removed from these ecosystems. Unfortunately predator research to date has been largely focussed on a single species of predator or prey. What is needed is more research into predator balance and the prey switching that may occur if a species is removed. The cat problem can be broken into three categories: domestic, stray and feral. The effects of each category of cat on native wildlife vary, as do the control issues. The most "difficult" category, politically, is the well-cared-for domestic pet as there is an acknowledged social role for the companion cat. But cats vary in temperament and many well-fed cats are still aggressive hunters. Can conservationists accept that cats should roam free to kill native wildlife? Many people organise their gardens to attract birds, obtain much enjoyment from watching them and view such birdlife as their "companions" with certainly as much right to life as a domestic pet. It is hard to get a handle on the size of the domestic cat population since with no requirement to register cats, the figures are estimates only. Cat ownership in New Zealand is high, with around four domestic cats for every dog. A "survey" by a cat

food manufacturer put the total number of domestic cats at 830,000. Figures on birds (both native and introduced) killed by domestic cats are contradictory but most estimates put it in the tens of millions a year. I have personally seen kingfishers, silvereyes, thrushes and blackbirds killed by cats. Another Forest and Bird member noted 25 deaths in one year including two kereru. The second category of cat is the abandoned domestic pet. These are "street" cats and are not truly feral. They are often undernourished and inbred, and rarely survive more than three years. Generally not able to live in the wild they depend upon domestic scraps, garden birds and wildlife. Their offspring become wilder, more difficult to domesticate and more reliant on wildlife kills for food. Stray cats may migrate to add to the population of the third category — truly feral cats. These animals live away from human habitation and are wholly reliant upon wildlife kills. ’ It is on islands where feral cats are the main threat to native animals. In these simpler ecosystems birds will often make up more than half of the diet of feral cats. Cats are, or have been, present on at least 25 New Zealand islands larger than 100 hectares including large, biologically important sanctuaries such as Raoul, Auckland and Campbell Islands. They are thought to have been implicated in the extermination of at least five endemic species, such as the Stephens Island wren

The lighthouse keeper’s cat

HE STORY OF THE Stephens Island wren provides a tragic example of the danger of cats as predators of native wildlife in the relatively simplified ecosystems of small islands. This remarkable wren — the only flightless perching bird (passerine) known — has the unenviable distinction of being possibly the only bird to be discovered and exterminated in the same year. A domestic cat was responsible for both events. The lighthouse keeper on this northern Marlborough Sounds island, David Lyall, reported that in late 1894 his cat brought him around 17 specimens of an unusual wren-like bird. The following item appeared in the Christchurch Press in 1895: "At a recent meeting of the Ornithologists’ Club in London, the Hon W. Rothschild, the well-known collector, described this veritable rara avis, specimens of which he had obtained from Mr Henry Travers of Wellington, who, we understand, got them from the lighthouse keeper at Stephens Island, who in his turn is reported to have been indebted to his cat for this remarkable ornithological ‘find’. "As to how many specimens Mr Travers, the lighthouse keeper and the cat

managed to secure between them we have no information, but there is very good reason to believe that the bird is no longer to be found on the island, and as it is not known to exist anywhere else, it has apparently become quite extinct. This is

probably a record performance in the way of extermination. The English scientific world will hear almost simultaneously of its discovery and of its disappearance, before anything is known of its life-history or its habits."

(see box above), as well as some 70 local extinctions. It is in retrospect, when cats are removed from an island, that their full impacts can best be seen. On Little Barrier Island and Tiritiri Matangi, for example, once cats were eradicated, native wildlife recovered and other native species were successfully reintroduced.

N MAINLAND FORESTS, mice, young rats, rabbits, native insects, skinks and geckos are more important components of cat diet than birds. Needing to eat 100 weta a day to substitute for other dietary items, feral cats in some areas may significantly reduce the population of native insects and reptiles.

The role of feral cats in reducing the juvenile population of other predator species is significant. A study by B.M. Fitzgerald and B.J. Karl in the Orongorongo Valley near Wellington showed that rats provided the staple diet of cats — up to 43 percent by weight. The study suggested that cats ate up to twice the "standing crop" of rats and imposed a major check on rat numbers. When cats became scarce (probably as a result of intensified possum trapping) the rat population quadrupled. Rabbits and possums were also significant: prey. items: for cats in the Orongorongo study, although it is likely that possums might be an anomaly here as they have not been detected as a significant part of cat diet in other mainland studies. Stoats, which are significant bird predators, were also included in small numbers in the feline diet. Ground feeding birds in the Orongorongo made up less than five percent of cat diet by weight. These were mainly blackbirds and thrushes, followed by silvereyes, chaffinches, fantails,

hedgesparrows and native pigeons. But rare and threatened birds — because of their very rarity — are unlikely to show up in studies of predator diets even while the predator may still have a damaging impact on the threatened population. This is the case with ground birds such as young kiwi and New Zealand dotterel. Although they are not a significant component of cat diets, their populations are thought to be seriously affected by cats. In areas with large rabbit populations these animals form the main diet for ferrets and feral cats. Where rabbit numbers declined, the predators switched more to lizards, insects, hedgehogs and ground dwelling birds. A study by Richard Heyward and Grant Norbury in Central Otago, found that the switch to birds was quite significant. The little research information that is available thus suggests that the removal of feral cats from mainland forest areas will not necessarily result in an increase in the native bird or reptile population. A study in the Mackenzie Basin by DoC scientist Ray Pierce suggested that a decline in ferrets and cats may lead to an increase in the stoat population. Feral cats may thus possibly have a net beneficial effect by killing stoats and young rats, and these two other predators are likely to increase in numbers if cats are removed.

In sensitive environmental areas, however, where cats are known to be the main predator of a particular species, such as in the black stilt habitat of the Mackenzie Basin or the New Zealand dotterel breeding grounds of Stewart Island, there is good reason for local cat-specific control or eradication.

)) N AUSTRALIA, where cats eat small _ native mammals, they are probably a "bigger problem than here. The Australian National Parks and Wildlife Service estimates that each domestic cat kills eight birds, eight reptiles, and sixteen mammals a year. At a recent cat control conference in Sydney the suggestion was

: Cat diets

made that, as a night time curfew was not sufficient protection, domestic cats be confined indoors 24 hours a day to protect native wildlife. In Victoria much work has been done on encouraging responsible ownership. The Domestic (Feral and Nuisance) Animals Act 1994 empowers councils to control both dogs and cats to protect the community and the environment. Registration is required for each animal, with owners being issued an identification marker. If you request a pet owner to prevent his or her dogs or cats entering

your property the owner will be guilty of an offence if the pets then enter or remain on your property. It is an offence if dogs are found at large outside an owner’s property between sunrise and sunset or, for cats, between hours specified by the local council. In environmentally sensitive areas, at a distance estimated to be beyond the normal range of domestic cats, all cats are regarded as vermin and park rangers are empowered to shoot them on sight. Councils may also prohibit dogs and cats from certain public areas or impose

conditions as to times or required restraint. Such animals found in conservation zones may be destroyed, as may those which do not bear an identification mark and which are wild, uncontrollable or diseased. ~ HAT CAN WE DO in this country? Our objective should be to reduce the predation by cats of native birds and reptiles in urban areas and to reduce recruitment to the feral cat population. In the absence of any national legislation on cats, control measures are currently the responsibility of either regional or local councils. Councils should develop policies which encourage responsible ownership, lead to a reduction in the cat population by controlling breeding, and remove abandoned, stray or unwanted cats by humane methods that meet the concerns of animal welfare agencies. Some councils, however, see the issue as too much of a hot potato, are unwilling to consider the problem, and claim that they have no powers to act unless there is national legislation. Other councils already have bylaws which cover cats under their "animal control" activities. Government auditors have approved such council expenditure thus confirming that all councils do have the necessary powers. The issue of cat control and cat registration is fraught with emotion. Would registration necessarily decrease the number of cats, or the impacts on native wildlife? Stephen Layton, chief inspector of the Wellington SPCA argues that registration would help reduce the large number of stray cats which feed into the feral population. While the SPCA is generally supportive of the idea of registration as a basis for promoting responsible ownership and a way of linking predatory animals with their owners, it feels that while dog control is given so little priority by local government, cat control is probably at present a nonstarter. Policing of cat registration would also be more difficult than for dogs which are generally more obvious and less secretive. Another form of control is to limit the number of cats per household. This is already the case in North Shore city which has a generous five-cat limit (kittens under three months excepted). Other possibilities are that only registered breeders of cats should be permitted to own cats which have not been desexed, and to include in council

Cats, rabbits and RCD

ATS, ALONG WITH stoats and ferrets and harriers, are the main predators of rabbits. Any introduction to New Zealand of the Rabbit Calicivirus Disease (RCD), currently decimating rabbit populations in Australia, is likely to kill lots of rabbits. Once the rabbits die, their predators will probably start switching to native species. It is possible also that the decline in a rabbit population will lead to reductions in feral cat numbers. This would result in higher numbers of rodents which are major diet items for stoats. More rats and stoats will likewise have a greater impact on native species. The permutations are complex but DoC estimates that there are about 20 native species in rabbit areas at risk from "prey switching" by predators. These include tussock grassland and river bed species such as the grand skink, Otago

skink, scree skink, black stilt, wrybill, banded dotterel, black-fronted tern, and Caspian tern; coastal species such as yellow-eyed penguin, New Zealand dotterel and New Zealand fairy tern; forest species such as yellowhead and kaka, North Island weka, brown kiwi and kereru; and wetland species such as brown teal, southern crested grebe and scaup. Some of these animals are already severely threatened, and any increased predation in key areas may be catastrophic. Protection of them will require a massive predator trapping programme requiring considerable extra funding. There will be a public consultation process once the group applying for the introduction of the virus has lodged its application, which is expected within

the next month or so.

bylaws the requirement that animals may be kept as pets "providing that they do not create a nuisance". In environmentally sensitive urban areas, such as near bush reserves, wetlands or parks with a native animal population, the ownership of cats could be prohibited by councils unless they are confined indoors or in a totally enclosed pen. In less sensitive but still important wildlife areas a night curfew could be imposed by councils. For feral cats, there is still insufficient research information to be sure of the effects of their removal. Until better information is available on feral cats we should consider, where achievable, eradicating cats on islands that have significant conservation values. Larger islands and mainland areas are more difficult, but, in suitable high value conservation areas, cat-free zones could be established where residents cannot introduce new cats and any existing residents with cats would be required to have them

desexed and not replace them upon the cat’s death. This was a voluntary restriction successfully developed by the residents of Australia’s Lord Howe Island to protect the island’s rare native woodhen. It has also been promoted by Forest and Bird as part of a "pest-free" covenant on titles for new subdivisions in ecologically sensitive areas (see February Forest & Bird page 12). Generally the removal of feral cat populations should be part of a planned timetable and programme to remove all introduced predators in a given area. Consideration must be given to the effects of changes in predator balance on remaining predators and the wildlife which

makes up their diet. KEN CatT is a member of Forest and Bird’s national executive.