Cats aren’t evil, but they are a problem

By David Winter 22/01/2013 20


It seems Gareth Morgan has declared a war on cats. It will, I’m sure, come as a great surprise to you that Morgan’s description of cats as ruthless and sadistic killers that we must eventually purge from the land  has met some opposition. Invoking outrage is pretty good way to get free advertising in New Zealand, and if you measure the campaign’s success in tweets, comments and talkback calls I guess Morgan is on to a winner. But I’d like to think we can do better than simply setting up an argument between supporters of Morgan’s Maoist purge and cat lovers who think their moggie can do no harm.

Cats are a problem

Most of the reaction to Morgan’s campaign has been to basically treat it as a joke. We should be clear then, that introduced predators are the number one threat to New Zealand species. Stoats, weasels possums and rats all contribute the decline of birds and lizards (and invertebrates, though we don’t monitor those species closely enough to track their progress). Cats are certainly part of that problem. They have contributed to the extinction of at least 6 bird species  in New Zealand, and many more populations and subspecies have been lost partly as a result of predation by cats (Merton, 1978). Cats continue to pose a threat to our wildlife. The impact of feral cats on shorebirds  (plovers, dotterels, oystercatchers) and kakapo is well documented (Karl and Best, 1981 doi: 10.1080/03014223.1982.10423857). In the space of a week one cat managed to kill 102 native short tailed bats.

The problem isn’t restricted to wild cats. Pet cats will attack and kill native birds and lizards when they have the chance. In Dunedin the impact of tame cats is large enough that it’s been estimated local bird populations (including natives) wouldn’t survive if they weren’t replenished by migrants from around the fringes of the city (van Heezik, et al. 2010. doi: 10.1016/j.biocon.2009.09.01)

Getting rid of cats isn’t necessarily a solution

It’s clear then, that cats are a problem for the conservation of native wildlife. But it’s not nearly as clear that simply getting rid of cats will be much help. Every study of the diet of cats in New Zealand has found that cats kill a lot of mice and rats. These rodents are themselves predators of birds so removing one predator from our country may simply let another run amok. When feral cats were removed from Little Barrier island it led to an outbreak in kiore (Pacific rat), which threatened Cook’s Petrel populations on that island (Rayner et al, 2007 avaliable via PMC ).

Should we phase out cats in New Zealand?

So, if Morgan’s plan was actually do-able, should we do it? I have to honest here and tell you, I don’t know. It’s abundantly clear that cats, both feral and domestic, can kill native animals. It’s clear that in at least some cases that killing can have a major impact on populations, but removing cats might not help all that much. If you want to know whether the impact of your typical urban moggy justifies Morgan’s campaign, especially given the abundance of rats in New Zealand, you’d have to ask a conservation biologist. That’s something no news organization has bothered with yet, as far as I can tell.

Is this the conversation we should have started?

It’s fairly obvious that Morgan’s website, with its strange anthropomorphism (cats are predators sure, sadists? no) was designed to draw headlines and “start conversations”. But what hope is there for environmentalists in conversation where our side wants to take people’s kittens away?

Introduced predators are the biggest threat to New Zealand’s biodiversity, so the goal of eventually controlling these predators so tightly that they no longer pose a threat is a very worthy one. But the sort of change required to get us from today, where only 12% of the conservation estate is managed for predators, to that goal has to come from the ground up. Picking fights like this will get you headlines, but I don’t think it will change anyone’s mind.

Merton, Donald V. “Controlling introduced predators and competitors on islands” pp 121-128. In Temple, S.A. (ed.) Endangered birds: management techniques for preserving threatened species 1978

(image at the top via Pauline Dawson/ArtAndMyLife)

20 Responses to “Cats aren’t evil, but they are a problem”

  • If our two two-year-old cats are anything like representative then cats kill about 10 times the number of rats and mice than they do birds. However lizards are another story, although I catch and release about half the lizards that the cats bring inside. The other half are eventually discovered dessicated under furniture.

    The benefits of cats to humans is also well documented. So removing cats could be considered harmful to humans.

    Really the discussion should be focussed on sterilisation to reduce the wild cat population, but as you say removing a preditor can have unintended consequences. Sterilisation of the majority of urban cats would probably do some good and be a much more palatable proposal for a cat loving population.

  • I would just like to say that as a member of the cat community, our depredations to birds are miminal compared to the large monkey-type introduced predator that dominates New Zealand. Just go to the poultry section of any supermarket, or indeed KFC to see how many birds *they* go through.

    But I don’t think that we kittens should get rid of the many such “humans” that we keep as staff. They serve a useful function in feeding us, and some of the smaller ones are quite adorable in their own way. Possibly “stray” humans not under the care of kittens should be neutered, although some might consider this excessive.

    Anyway, this is lying in the sun weather, not bird chasing weather.

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  • I’ve got a better idea:

    Let’s get rid of the rich old white guys… you know, property developers… bankers… rentiers… people who invest in industries that pollute and destroy natural habitats etc. You know the ones I mean – the Gareth Morgans of this world.

  • Hey, great article thanks, but I should point out the text gets a bit unclear from “Is the conversation we should have started?” on. Nothing major, but a few typos seem to have obscured some of your points.

  • Clearly a case of tarring all cats with the ‘ruthless and sadistic serial killers’ brush. Our moggy, despite hours of peering adoringly at feathered creatures, has yet to capture (let alone kill) anything at all.

  • Great post, David – a nicely reasoned response to a fairly odd call from Gareth Morgan. I had thought that the “if you take away all the cats then rats will flourish instead” evidence was quite clear, and well known, but obviously Morgan hadn’t heard it, and hadn’t bothered to do any research before leaping into print.

    We have a cat, and her hunting skills seem to be largely non-existent. Or perhaps she has simply learned to hide her kills from us, given that the one time she brought in a tui we scolded her and chased her out and made it as clear as we could that tui were for looking at, not touching. We keep her inside at night, and she has been desexed. I think that’s all okay, on balance.

  • Cheers for the comments all, especially about typos which I’m terrible for.

    Pete, it’s not a great solution, but the copyright transfers we sign away to publish papers allow us to provide copies to colleages. If you want to see the full paper one way to do it is contact the lead author.

    (Mike’s piece is very interesting, all I’d add in defence of my articles being behind paywalls is that open acess publishing is (usually) expensive, and I don’t have funding to cover it)

  • Well, to balance some of the subjective anecdotes with an alternative subjective anecdote, our cat wasn’t just a serial killer, he was an indiscriminate axe murderer, and it was all instinctive. :(

    Thanks for the insightful post. Whether phasing out cat owneeship is a reasonable path, it’s important to get people talking about this.

  • I have a sneaky suspicion that to achieve the intended goal you’d have to eliminate all small mammals: mice, rats, weasels, stouts, etc., as well as cats and possibly dogs.

    There are all introduced species and one way or other affect native wildlife.

    Slightly off-topic, perhaps, I have seen extraordinary (to me) “booms” in rodent numbers sometimes in the bush.

  • In the US it is unusual for cat owners to let their cats outside. Being a subscriber to online American vet blogs ( means I get quite a lot of posts about the benefits of inside vs outside cats (for example It’s interesting that in NZ we seem to have the opposite view – in fact when I tell people my cats are almost-always-inside cats (for multiple reasons) they look at me funny and suggest that it’s cruel.

    Plus, my cats make me happy.

  • interesting that all sorts of logic-defying arguments come out for this one. EG, no point doing it since dog and stoats are just as bad, no point doing it, there would be an explosion in rat and mice population, no point doing it cats are excellent companion animals, no point doing it I watch my cat and it never kills anything, Gareth Morgan is an animal hater, humans are worse than cats…

    Take the cat-centric specifics out and it reads like a climate change deniers network response to a suggestion that we produce less CO2

  • @Ashton, do you know anyone who gains immense pleasure from cuddling CO2 particles? Elderly people, perhaps, whose main activity on an otherwise lonely winter evening is spent half-dozing on a Lay-z-boy stroking their CO2 particles?

    Get my point?

  • I know a few elderly types who emit huge quantities of methane – is that similar? Yes, I get your point, I just happen to disagree with it.

    It would be reasonable if cats and their owners were subject to the same restrictions as dogs and their owners. Regardless of the beautific image of a geriatric drooling in pleasure over the touch of immobile purring fur, the reality is that cat is often on its own recognizance. There is absolutely no way of the individual knowing what the cat is doing in that time except that it is reasonable to assume it behaves according to its genetics ie it goes looking for something interesting to play with and probably kill.

    No dog is allowed such freedom. Any dog shown to have attacked and killed another animal would be subject to an order to restrain as a minimum. Repeat offenders would be destroyed.

    If my dog was to wander into your backyard and defaecate on your garden (with or without an old person stroking it) you would likely be offended, irritated and, backed by the law, you would require me to restrain and control my dog.

    My cat and yours meanwhile can freely shit where they like, safe in the knowledge they are legally allowed to do so.

    Not only is this iniquitous, its illogical. Forget about the native birds a minute – the entire situation is just wrong.

    If owners were willing and able to take real responsibility for the actions of their companion animal I would be happy for them to have tigers and hippo’s in their lounge. The reality is that cat owners (as a class) don’t have those capabilities – nor do they necessarily even have a desire to achieve those capabilities. They wish to continue the self delusion that Tabby wouldn’t hurt a fly, or worse, just figure I and the rest of the population should just lump it.

    Bird life included.

    #Disclosure – we have a cat….

  • Hah, nice response.

    “There is absolutely no way of the individual knowing what the cat is doing in that time….”… Except if it is an inside cat.

    Not sure if you saw my other comment above, but my cats are almost-always-inside cats. One of the bonuses of this is the pooing in gardens thing! Sometimes when they’ve been having outside time they’ve do it in our garden, they’ve done it in the neighbour’s. It’s embarrassing, not to mention disgusting and unhygienic.

    I agree with the restrictions on cats (in line with dogs as much as possible). It would also help in a plethora of other ways when it comes to numbers control, animal welfare and animal education. Unfortunately, as with dogs, there would be people who don’t register (or whatever) and get away with it, and the good people like us will be left with paying the council fees. But if that’s what it takes for me to keep my cat… of course I’d do it.

  • Cats catch most of their prey at night, or at least is when our cat brings in his bloody offerings. After he brought us a large live rat at 4.00 am, which terrified me, we have kept him in at night. We lock his cat door at around 9pm and open it first thing.
    We bought a litter tray but he doesnt use it and after an initial sulk has got used to the new arrangement quite quickly. So how about setting a curfew for cats?

  • As much as I’m inclined to agree that there’s more to the problem than simply getting rid of cats, I’m uneasy accepting that a cat only hunts and kills species X at time Y because that’s all its ownee sees. There could be much more going on there, too. In Slinky’s case (our former cat) he seemed to be bringing us presents at certain times, like if we’d been out all day and came home, but he rarely brought us bird corpses in spite of the times we saw him creeping and sprinting up near-vertical cabbage tree trunks in the garden. I’d be surprised if he didn’t have fair number of birds in his tally, but I’m not sure if we ever saw them.

  • The issue to me about cats is not so much the relatively few adult birds they catch, but the number of nests of chicks they destroy.

    In our garden in the past 4 years we have had a blackbird brood wiped out every year before the chicks were able to fly. The local cat patrols, it hears the chicks cheeping, locates the nest by watching the parents fly to and fro feeding, and then at night climbs up and to destroy the nest and kill the chicks.

    One year the blackbirds nested in a spiky bougainvillea that the cat could not get into, so it just waited until the chicks were ready to fly and had a field day as the chicks fluttered from the nest to lower branches – the blackbird parents’ plaintive calls waking me at dawn just in time to witness from an upstairs window the murder of the last of their children.

    As the younger generations of birds are lost and never breed, who can be surprised the local bird population dies out? It is quite clear that cats, even those fitted with bells as the local predator that comes to our garden is, are significant culprits in this ethnic cleansing of our feathered planetary companions.

    In 2013 we have set up a infra red web cam viewing the latest blackbird nest and we expect to be able to donate a short video of the final minutes of this year’s 2nd brood of blackbird chicks on Gareth Morgan’s website shortly – assuming the same carnage as we have seen the past 4 years is revisited on that nest in the next week or two.

    And to be fair to cats, we’ll send it even if it reveals the culprit is actually a stoat, weasel, rat or other beast … but I am not holding my breath on that!

    So what is the purpose of Gareth Morgan’s website? It seems to me it is to raise awareness of the number of cats and the damage they do, and to encourage discussion about how best to manage cats to protect the local bird population.

    That is a worthwhile discussion to have; and looking what some Australian states have achieved with their regulation of cats (and similar actions taken elsewhere) should be guiding our thinking on how to resolve the issues the cat website raises.

    Of course the other thing we must do is make sure that our local politicians understand there are votes in sorting sensible cat management – otherwise nothing will happen.

    Personally I hope the Morgan millions raise sufficient awareness and discussion by the population for the regulators to take note and consider the issue.

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