Updated: Cats’ impact on native wildlife – Experts respond

A campaign launched by economist Gareth Morgan to raise awareness about the impact of cats on native wildlife has elicited a range of opinions, but what does the evidence say?

This week , Dr Morgan launched the Cats-to-go campaign, calling for further efforts to prevent cats killing native birds. Recommendations included: affixing bells to collars, keeping cats indoors, neutering, requiring registration and microchipping for cats and — more controversially — calling on cat owners not to replace their pets when they die.

You can read more about the website and the extensive media coverage it has received here. Bloggers Dr David Winter and Dr Wayne Linklater have also written about the issue on science blogging network Sciblogs.co.nz

The Science Media Centre gathered the following comments from experts on predator control and conservation. If you would like to contact a New Zealand expert, please contact the SMC (04 499 5476; smc@sciencemediacentre.co.nz).

Dr Alistair  Fairweather, Department of Conservation, comments:

“Dr Morgan has expressed concerns about the high level of cat ownership in New Zealand and the threat cats pose to our native wildlife. He is advocating for responsible cat ownership and encouraging people to consider not replacing pet cats when they die. What Dr Morgan is saying and promoting is broadly supported by current research and in line the Department of Conservation’s (DOC) views.

“A feral cat is a cat living independently of humans and breeding in the wild. Their populations are self-sustaining, although they may be supplemented by unwanted domestic cats that have been dumped. While feral cats feed mainly on rabbits and rodents they also have an impact on native birds, lizards, bats and insects. There are many examples where feral cats have contributed to the decline of native species in New Zealand. To reduce the impact of feral cats on native wildlife, there are a number of sites around New Zealand where they are controlled by the Department of Conservation and community groups.

“Domestic cats are companion for many people. However, they are predators, and given the chance, will hunt. Many of the animals caught by domestic cats around cities and towns are rodents or non-native birds. Domestic cats, especially those living near native habitats, have been reported as catching native birds (including kereru, tui, fantails, grey warbler), reptiles (such as common skink and the rare gold-striped gecko) and native insects. It is difficult to estimate the scale of domestic cat predation on native species because domestic cats only bring home about 25% of their prey, the rest being eaten or left were it was caught.

“DOC supports responsible cat ownership and there are a few simple actions cat owners can do to help protect native wildlife.”

  • Don’t dump unwanted kittens, give them to the SPCA or have them put down.
  • If you live near an area with native wildlife, keep your pet well fed and indoors at night.
  • Attaching a bell to your cat’s collar can also help as it makes it harder for them to stalk silently.

Cath Watson, President of the Companion Animal Society of New Zealand Veterinary Association, comments:

“Dr Morgans dream of eliminating cats from NZ is laudable from a conservation viewpoint, but unrealistic in reality and cannot in itself solve the issues surrounding endangered wildlife in NZ.

“There are a number of factors that would have to be taken into account before targeting solely cats can be considered:

  • Cat are just a part of a wider ecosystem and do not just prey on birds. They will also reduce the populations of other pest such at mice, rats, and rabbits. Removing cats from the ecosystem may have unforseen consequences on the ecosystem as a whole, also to the detriment of native wildlife
  • Habitat destruction and competition for food sources from introduced species such as rabbits, possums, insects and introduced bird species also have a huge impact on NZ native wildlife, arguably more so than owned cats
  • The important role of cats in households. 83% are currently considered a member of the family and most of these are kept for their companionship role or education for children. Cats can play a very important role in human health, bahviour and wellbeing.
  • There are currently no controls on who can own cats, what the responsibilities of cat owners are, what areas there are may not be suitable for cat ownership, and how many cats a person can own.  This would be a better starting point for managing the NZ cat population

“There are also three classes of cats that need to be taken into account:

1) True feral cats who have no dependence on humans for survival at all. These cats have to be highly capable killers just to survive and are likely to be the greatest threat to NZ wildlife.

2) Stray cats – these cats often have many of their needs directly or indirectly met by humans – often living in shelter provided by human habitation and existing by scavenging, or sometimes fed by members of the public. They interact and interbreed with pet populations.  They also contribute to predation of vulnerable NZ native species such as birds, skinks and geckos.

3) Owned domestic cats have a human directly responsible for their welfare needs of food, water, shelter, health needs etc. These cats are more likely to be occasional killers to satisfy behavioural needs rather than as a source of food.

“The Companion Animal Society of the NZ Veterinary Association recognise feral cats as being the greatest threat to NZ wildlife and they have the least value to society, except as random pest control. Stray cats contribute more positively to NZ society but still require responsible management and monitoring to ensure their impact on native fauna is minimal. The third group of cats are family members, where education on responsible pet ownership would have much greater benefits not only to nearby wildlife, but also the cats and the families they belong with as well.

“Gareth Morgan would do well to direct his energies to eliminating feral cats, dismantling stray cat populations and encouraging responsible cat ownership and legislation to support it. This could be achieved by legislating (central government) that all cats should be microchipped, all non – breeding cats are neutered, and cat ownership regulated by local councils (eg define number of cats permitted /household, ban cat ownership in sensitive areas for NZ wildlife).

“From an individual cat owner perspective, the responsibility lies around ensuring there is whole of life care for the cat. It means there is somewhere safe for the cat to be when on holiday or in the case of a change of living circumstances. It means restricting the cat’s access to the outdoors at the high risk time to both cats and wildlife i.e. dawn, dusk and overnight. It means providing behavioural enrichment and a suitable food and water supply to reduce the cats need for predation. It means desexing, microchipping and providing suitable health care for the cat. It means being aware of the surroundings you live in and what is safest for both the cat and any native wildlife before taking on the responsibility of cat ownership.”

Should consideration be given to the fact that cats do prey on other pests that harm native wildlife?

“Absolutely. It is the reason some people have cats in the first place. You cannot eliminate one predator without controlling all pests at the same time in an ecosystem. Remove cats and you may find a boom in rat and mice populations as a result. While his aims are admiarble, eliminating cats alone won’t solve NZ predation issues on native wildlife. You also have to look at the issues of competition for food sources from introduced birds, possums etc, as well as habitat destruction which also play a huge role in the success and decline of endangered species

“Responsible pet ownership centres around pet owners being aware of their legal  & moral responsibilities as well as what their pet needs for optimum health and wellbeing. It also means showing empathy, compassion and a sense of responsibility towards all animals. This includes:

  • a commitment to ‘whole of life’ care
  • provision of appropriate food, water and shelter
  • provision of a safe environment & containment that allows for adequate control of access to the road, toxins and other hazards
  • providing environmental enrichment to avoid behavioural problems
  • adequate holiday arrangements to ensure the safety and welfare of the pet
  • adequate arrangements if the owners circumstances change to ensure the pet is not abandoned
  • desexing or fertility control of pets to prevent unwanted litters
  • seeking veterinary assistance for any health problems as well as regular health checks, worming, vaccinations
  • adequate arrangements to cover health care needs of the pet eg pet insurance or a savings account
  • understanding, accepting and following council bylaws for public safety and the preservation of ecologically sensitive areas
  • identification, preferably by microchip, of all pets

“More specifically in this case, to reduce predation of native wildlife, considering keeping the cat indoors is a reasonable demand. However, it will not suit all lifestyles of owners and may result in serious behavioral consequences for the cat and owner, and needs careful consideration to the cats environmental needs. We would strongly recommend keeping cats indoors overnight and especially around dawn and dusk. Not only does this reduce the risk of predation, it also reduces the risk of misadventure for the cat.”

Dr Yolanda van Heezik, Senior Lecturer, Zoology, University of Otago, comments:

“There have been three published studies quantifying the prey caught by domestic cats in New Zealand (in Auckland, Christchurch and my study in Dunedin) and they all agree in reporting that pet cats catch birds, including native species. Cats appear to catch species in proportion to their abundance in the environment, so in Dunedin, the two most abundant bird species (silvereyes and house sparrows) were the two most common bird species caught by cats. Cats in the Dunedin study also caught native species such as fantails and bellbirds. Fantails seem to be particularly vulnerable. My study identified that about one third of cats did not bring any prey home, about a half brought back prey infrequently, but that about 20% were frequent hunters. The average number of prey brought back per year was 13, but that included rats, mice, lizards and invertebrates. It should be borne in mind though, that a recent study using Kittycams in the US reported that cats brought back only one third of the prey that they actually caught and killed, so the NZ studies probably under-estimated total numbers killed.

“I support Gareth Morgan in his campaign to raise awareness about the impacts that pet, stray, and feral cats have on our native wildlife. I suspect that most people have never given the issue much thought, or they think that the one or two birds caught by their own cat makes no difference. People need to consider that cats exists across cities at a density of about 225 per sq km, and that even though individual cats may catch few birds, cumulatively the total of birds killed is large. Other countries such as Australia have regulations in place around cat ownership and cat movements, and we need to start thinking along the same lines, if we value our native wildlife, and want to live in towns and cities where we can encounter native wildlife as part of our everyday lives.

“Feral cats are known to be a problem. The impact of pet cats is less well known. Because pet cats are fed, they are referred to as subsidized predators. They are more likely to hunt wildlife populations to extinction, as they do not rely on wild prey for food, so they are less likely to switch to alternative sources of prey when their prey population becomes so depleted it costs too much energy to hunt for it.

“Stray cats are an important issue. Stray cat colonies that are fed by the public still kill wild species. Well-fed cats hunt. TNR policies (trap-neuter-return) have been shown in other countries to be ineffective at controlling stray cat populations.

“Cats do prey on rats, which are also significant predators of wildlife. This is an argument for carrying out simultaneous rat control in areas where cats are absent.

“The recommendations given by Gareth Morgan are reasonable: consider using a collar with a bell: our research has shown they reduced catch by 50%. There are other devices to curb cat predation, such as the catBib, and I suspect more in development. Consider keeping your cat inside at all times. This ruling is in effect already in some parts of Australia. And consider not replacing your cat when it eventually dies.

“I’m currently involved in a study coordinated by Assoc. Prof Mike Calver at Murdoch University in Australia, surveying the public in NZ, Australia, the UK and the USA to ascertain the opinions of the community on cat ownership and regulations around ownership. The results from that study should be available later this year.”

Mr John Innes, Scientist – Biodiversity and Conservation, Landcare Research, comments:

“On his website, Gareth Morgan paints a broad picture of cats as major predators of native birds in New Zealand (‘cats are wiping out our native birds’) and suggests that New Zealand without cats  is ‘a New Zealand teeming with native wildlife, penguins on the beach, kiwis roaming about in your garden.  Imagine hearing birdsong in our cities’.  However, careful reading of the site does show that its authors are aware that there are other predator species to consider besides cats.  They refer to cats being ‘one step’ towards a Predator Free New Zealand.

“The impact of cats  – whether feral or pet – on valued wildlife remains controversial because it is site-dependent and ecologically complex, and because key impact questions are frequently unresearched.  The website cites Medina et al (2011) regarding birds threatened or made extinct by cats, but this is a worldwide study of islands and not just New Zealand, and effects of cats are frequently additive to those of other predators, especially rodents, and habitat modification.  In New Zealand also, cats alone cannot be blamed for the loss of any species.  However, they are undoubtedly key contributors to declines of some birds (and other fauna) in some places, for example black stilts, black-fronted terns and wrybills in braided rivers and other shorebirds trying to nest on beaches, but so potentially are hedgehogs, ferrets, stoats, four wheel drive vehicles, people walking dogs and fishermen.  When cats, ferrets and hedgehogs were targeted in Mackenzie Basin braided rivers, possums and Norway rats then ate the black-fronted terns.

“Cat diet studies in New Zealand urban areas (e.g. Gillies & Clout (2003); van Heezik et al. (2010)) show that cats eat small mammals, birds, lizards and invertebrates.  The birds are mostly common introduced species or widespread natives, especially silvereyes.  The research to clarify whether the negative effects of cats on these fauna outweighs the positive effects of their predation on ship rats, Norway rats and mice has not been done.  However, keeping cats inside, especially at night, will negate these possible positive effects.  Urban sanctuaries like Zealandia in Wellington clearly change this context because highly threatened species like saddlebacks may be taken by cats, but it is likely that they would be taken by ship rats or possums anyway if cats were removed.

“In New Zealand native forests, ship rats are the major prey, and this little-seen predator eats many more birds than cats do.  The Gareth Morgan website refers to kaka, kokako, weka, mohua, t?eke and robins as endangered, perhaps implying that cat control might help them, but cats are not significant predators of any of these species, except  possibly weka.

“I agree with the website that ‘we need to control cats and rats together’, and in fact recent thinking around a Predator Free New Zealand has always focused on several species, usually stoats, ship rats and possums.  Whether mice, hedgehogs, Norway rats, ferrets, weasels and cats may yet be included is still unfolding.

“In the meantime, pet cat owners should educate themselves about the possible threats of their cats to local wildlife, and they should plant trees and shrubs suitable for native wildlife.