Cats and Triffids

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JANE: So, Alan, you were telling me about how cat-friendly New Zealand is, and how

Kel in Her Natural Habitat

Kel in Her Natural Habitat

your cats wander freely around outside.

ALAN:  Yes, they go wherever they wish to go. The only fly in the ointment is that they might kill native birds and reptiles which (since New Zealand has no native predators) are quite easy prey. However, my cats mostly bring home rats, mice, and sparrows, along with the occasional blackbird. They’ve almost never brought home anything native.

JANE: That’s interesting – and good.  I was avoiding bringing up the fact that domestic cats are – in most parts of the world – an invasive species, because lots of people don’t want to face the fact that beloved Tabby is not a natural part of the wilds.  I’d heard that the kiwi bird was being endangered because it was being hunted by domestic cats.  Is there any truth to this?

ALAN: Indeed there is. And it isn’t just kiwis – we have many unique species, some of which do indeed hover on the brink of extinction as a result of predation.

JANE: Is there anything that can be done?

ALAN: There is a movement in New Zealand to make it illegal for cats to wander unaccompanied. An eccentric millionaire called Gareth Morgan is particularly vocal about this and has put a lot of money into the campaign, so far to no avail.

JANE: Interesting.  I could see why it would be hard to enforce, although if animals are “chipped” there, the way it’s becoming common here (it’s required in Albuquerque, even for indoor-only cats), it would be possible to trace the owners of unsupervised animals and fine them.

If you could catch the cat, of course, and hold it long enough to read the chip.

ALAN: Chipping is a legal requirement for dogs, though not (yet) for cats. However, while cats are certainly responsible for killing some native wild life, cats are actually far outnumbered by rats, weasels, stoats and ferrets – introduced predators that live freely in the wild and which are much more destructive of the native wild life than are well-fed domestic moggies.

JANE:  I’m guessing that rats came via ship, uninvited, but do you know how the weasels, ferrets and stoats got there?  What were they introduced to predate upon?

ALAN: That’s a bit complicated. In the mid-nineteenth century rabbits were brought to New Zealand for both food and sport. Being rabbits, they immediately had a huge population explosion and got out of control, to the despair of the farmers whose crops they were eating. So in the 1880s, stoats, weasels and ferrets were deliberately introduced in a vain attempt to try and curb the rabbit population. Unfortunately, the stoats, weasels and ferrets seemed to prefer dining on native New Zealand animals rather than on rabbits, and so the rabbits remain a problem to this day!

JANE: Australia had a problem with rabbits, too.  I recall a truly horrible description of hordes of rabbits dying in the summer drought that was the centerpiece of one of Arthur Upfield’s novels.

How does New Zealand cope with these feral predators?

ALAN: We have a government department (the Department of Conservation, known as DOC) whose brief is to look after the native wild life. To that end, they have put a lot of effort into making many offshore islands predator free, and these are kept as sanctuaries for the wildlife. There are also several areas on the mainland that are enclosed by predator-proof fences which are maintained as sanctuaries.

JANE: Does this technique work well?

ALAN: Yes it does. Their greatest success has been with the black robin. By 1980 there were only 5 black robins left alive, and there was only one breeding pair. The female was called Old Blue. To try and reverse the decline of the robin, DOC implemented an ingenious conservation effort. Every time Old Blue laid a clutch of eggs, they were removed from her nest and given to a tomtit to foster. Then Old Blue, having lost her eggs, would lay another clutch…

JANE: That’s really neat – although the tomtits must have been confused.  How did this work out?

ALAN: Today, there are more than 200 black robins – all descended from Old Blue and all living safely on a predator-free island. Old Blue herself lived to be 14 years old, a true matriarch.

JANE: Mother of her race, indeed.  Of course, without much genetic diversity, they’re still a very fragile population – rather like cheetahs.  Still, given the option, it’s a good effort.

Although I applaud the program to save the black robin, it isn’t really dealing with the invasive species – instead, it’s imprisoning the victims.  I don’t know if any similar efforts have been made in the U.S.  (although some of our readers might).

Here in the Southwest, where I live, the issue of invasive species of plants is a serious one – especially given the scarcity of water. A good example is the tamarisk, also called the salt cedar.  It was brought to the U.S. in the early 19th century, valued both for its appearance and for its ability to thrive in salty soils.

However, tamarisk is a heavy water user that propagates more easily than many native plants in the bosque  (that’s what we call the forested areas along the rivers here in New Mexico).  As a result, there are entire areas that are nothing but tangles of tamarisk.

Currently, there is an effort being made to eradicate tamarisk and replace it with native plants, but it’s not easy.  Whenever I see them, I’m reminded of your iconic (in that it’s the source of your nickname) SF novel: Day of the Triffids, because, like the creatures in Wyndam’s novel, tamarisk was introduced for many good reasons and proved to be a plague.

Does New Zealand have its own triffids?

ALAN: Indeed it does – gorse has been here since the early nineteenth century. Charles Darwin recorded seeing it in 1835 and it was very well established then. It was originally introduced to be used for hedging on farms, but it quickly got out of control. It loves the conditions here and it spreads like wildfire. In summer, the hills are covered with yellow blooms as far as the eye can see, and so are the farmers’ fields. Everyone hates it and millions of dollars are spent trying to control or eradicate it, with little success.

There used to be a wonderful advert on TV for a spray that could be used to control gorse outbreaks. An angry farmer is shown flying his helicopter over his fields and spraying the gorse, swearing and cursing at the terrible weed. But the spray takes a long time to work, of course, and the farmer simply can’t contain his impatience and his anger. So, in a fit of fury, he turns his helicopter upside down and uses the rotor blades to trim the gorse right back to the ground. Then he flies home, satisfied with a job well done. The name of the spray is superimposed on the picture and a voice-over suggests that it might be better to use the spray instead of trying to turn your helicopter into a massive weed-eater…

I haven’t seen the advert for several years now which is a pity. I always enjoyed it!

JANE: Definitely creative and amusing…

There’s a lot more to be said about the subject of invasive species, both in your country and mine.  Shall we continue next week?

ALAN: Yes, let’s.


7 Responses to “Cats and Triffids”

  1. Heteromeles Says:

    I went out with a friend to go kill some pampas grass (a weed where I live) last week. Invasive species certainly are a chore. Tamarisk is a real nuisance, too. Of course we won’t mention what the worst invasive species is…

    As for gorse, it’s a pest up in northern California, but not as bad as it is in New Zealand. Didn’t Peter Jackson use some old gorse trunks to make his model for Fangorn Forest in his LOTR movies?

    By the way, since I’ve gotten into this discussion many times, here in California (and I think in the US in general and England too), the definition of a native plant species is one that was here before 1492. Columbus’ voyage is a somewhat arbitrary date, especially in California, but the point is that the so-called Columbian Exchange he initiated is when plants and animals really started skipping across the continents, so entrance after that date is regarded as the standard for being a non-native.

    As I recall, England uses a similar definition (they were on the other side of the Columbian Exchange, so potatoes are not considered a native UK species). They also have another category of non-natives that were introduced by the Romans and later travelers. Those are plants that were introduced between around 50 BCE and 1492 CE. Plants that were in the islands before something like 55 BCE are considered truly native, as if the Celts were isolated aborigines in England and there was no international trading before Caesar opened up Britain to the wider world. This is snarky, but I suspect the practical issue is that the Romans left behind better records than the druids did, and that may have helped modern scientists figure out what the Romans introduced to Britain, as opposed to what the tin-traders introduced to Cornwall back in 1700 BCE or whenever.

    • Jane Lindskold Says:

      Nice historical perspective… Probably the term “invasive species” needs to be defined as those plants that get out of control in a new ecosystem, not those that need to be carefully cultivated.

      Lucullus brought stone fruit to Rome — peaches, I believe, and cherries. I don’t think anyone complained.

  2. Paul Dellinger Says:

    It strikes me that most invasive species problems have been brought on by us, either accidentally or because we imported something we shouldn’t have. Wonder what this portends for whenever we make it to other planets?

  3. Jane Lindskold Says:

    I think some ecosystems might argue that humanity is an invasive species NOW.

    • Heteromeles Says:

      See my comment about the most invasive species. That would be us.

      Anyway, there’s a distinction between invasive and non-native. Non-native has the definition above, but most non-natives aren’t particularly invasive. Similarly, some native plants are very invasive. A classic example of a native invasive species is the California poppy, which is invasive in a bunch of US states and Canadian provinces. Technically it’s native to the US, but until (white) people started spreading it about a century or two ago, it was limited to some part of the west coast. It’s so popular in wildflower mixes that it’s been widely spread both within the US and elsewhere. I even saw it invading other plant beds in the New York Botanic Garden. Kind of gutsy for a warm-weather plant from California.

      Incidentally, wildflower doesn’t have a formal definition in the US, so a packet of “wildflower” seeds in the US may contain non-native invasive species. Always read the label before spreading the seeds, especially out in the wild!

      • Jane Lindskold Says:

        Now that’s a really neat detail. I hadn’t really thought about invaders from the same general landmass, probably because I figured there were natural vectors — birds, esp. — that could spread them.


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