Cats aren’t evil, but they are a problem

 

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.