Cats, Rats and Mice

I've seen the occasional argument that cats shouldn't be contained because they keep the rodent populations under control. Unfortunately there is no evidence that our domestic cats are doing anything significant to keep rodents under control, and I think that the people arguing this case are often the same people who claim they don't have rats or mice on their property, or just want to justify not keeping cats safe.

Rats and mice species in New Zealand

Rats and mice are a huge problem in New Zealand; they wreck havoc on our bird life and make themselves unwanted guests in our homes.  We have 3 rat species and one mouse species - all imported. The main rats are the brown rat, or Norway Rat, and the Black or Ship rat.  The Brown is the biggest and an adult makes a fearsome opponent that few domestic cats will take on. The ship rat is much more manageable, and looks more like a very large mouse. 

Noomi will take on all comers. 
Top is an adult ship (black) rat, and below
the brown or Norway rat

Domestic cat hunting skills

Our domestic cats have instincts to hunt that cannot be turned off, but they do not always have the skills to deal with rodents - these are passed down from their mothers. 

Recent  research into well fed domestic cats also shows that they will hunt,  but often fail to kill rodents.  This is because they perform their hunt in a different sequence from a cat hunting to feed itself. A hungry cat will stalk, capture and kill, then play with it's dead prey before eating it.  A well fed cat on the other hand will stalk, capture then play with it's live prey - sometimes allowing it to escape - before killing.

So, if you have cats don't rely on them to keep your place rodent free, and don't pretend you don't have rats or mice. They're everywhere, and if you don't see them, it just means they're smarter than you and the first time you will see them is when you find one in the kitchen cupboard or hear them in your ceiling space and now you have a real problem. 

Why not encourage cats to hunt rodents?

We're lucky in New Zealand; our rodents do not carry hanta virus, or rabies or some of the other really nasty diseases and viruses. I have no problem with them hunting, but you do not want them eating rodents, and you should not rely on your cats to deal with rodents in your house or yard.

• They do carry toxoplasmosis, and if you every see rodents in the day time that have no fear of your cats - you should make every effort to kill them and dispose of the bodies carefully.  This is a classic sign of a rodent infected with toxo - a parasite that takes control the brain of the rodent to encourage them into being eaten by a cat! 
• Beware of poisoned rodents! You may not be using poison, but your neighbours might - and a slow/dying rodent can kill your cat, or at best cost you a lot in vet treatments.  Again, if you see rodents out in the open, looking sick - do the right thing and kill it as humanely as possible and then dispose of the body (preferably in your rubbish so that any toxins from the body do not leach into your soil).
• Last, and definitely least - you cat will pick up worms and other parasites if eating rodents.  Generally these are roundworms that are easily dealt with by your usual worming program, but better to be safe than sorry.

Get Trapping!

Please do not use poison.  It may be effective in the right circumstances, but it has significant problems, and is not recommended for the average urban yard.  

• It can take up to 3 days, and multiple feeds to kill a rat, and they often 'go home' to die - meaning in your walls, ceiling or wherever they are nesting.  
• Older style anti-coagulants require multiple feeds, and may not kill - in fact some rats are now resistant.
• New Vitamin D3 baits require a pre-feed, must be set up correctly or may not work\cause bait-shy animals.
• If you get a poison that says ' 1 feed will kill' be VERY CAREFUL.  This may be an older highly poisonous substance (arsenic etc) that will instantly (and very painfully) kill any pet that subsequently eats the rodent. It may even not be legal or you might need a permit to use.  Never use a poison given to you by 'a friend'.   There is no vet treatment for these pets.

• The bodies remain toxic; a poisoned rat can poison your pets, your neighbours pets, and even wildlife like morepork or weka. Most modern poisons are anti-coagulant types (brodifacoum etc)- a pet will receive Vitamin K and intensive care if poisoned.
• If baits are not secured the rat may run off with it and leave it somewhere it can be eaten by a pet or child - or it may contaminate your veggie garden or water supply. 
• You MUST check just as regularly as when trapping, and clean up all unused baits.  If you leave out old baits - they can contaminate your garden, or deteriorate to an extent where the dosage is so low that it allows rats to eat it and become more immune! 

Don't be tempted by live traps either.  It is extremely irresponsible to let rodents go somewhere else to make a problem for others.  If you do not check traps regularly, the rat will die from dehydration or startvation - this is inhumane and illegal! The alternative is to live trap and then drown the animal in the trap - drowning is a terrible (and also possibly illegal) way to kill any animal.  

A good strong snap trap or automated trap will kill very quickly, and the best designed ones will let you cleanly dispose of the bodies, and reset with very little 'yuck' factor.  Trapping also lets you know exactly what sort of problem you have - you see whether the bait is gone or not, you if the trap has been triggered by a cunning foe (or maybe a hedgehog), and you see the bodies (and what they are - adult or young).  

Snap Traps and more

You can spend a lot of money on traps, and devices, or commercial services.  Be aware, that if you hire a commercial operator, you will need to keep paying.  Getting rid of one lot of rats or mice, just makes room for the next wave.  There is no such thing as a rat free property in New Zealand.

I use a variety of traps, partly because I don't want to spend a lot, and partly because you will find that some rats will outwit one or more designs, but not all.  So the more traps you have set - the higher your success rate. I have looked at the DOC200 traps and the GoodNature auto-resetting ones and can't justify the expense over my cheaper versions for my small backyard.

My favourites

I have had by far the most success with plastic snap traps from Big Cheese or Cat-Cha rat traps.  Both are very similar design.  You can open and release the dead rat without touching it.  

Big Cheese Plastic Snap Trap	Cat-cha Rat Plastic Snap Trap	Big Cheese /Victor Std Snap trap

The victor and Big cheese standard snap traps are a good cheap way to add more traps at little expense.  They do a good job as backup in areas where you want to put lots of traps, but are messier to clear, and fiddlier to set (and more likely to grab a finger or mis-fire if you aren't careful). 

There are a few others I have also purchased, but the two plastic 'jaws' are the favourites and most reliable. 

You can rebait using a small demountable bait holder - Big Cheese bait holder unscrews from the bottom, cat-cha does the same through the top.  Big cheese often come with preloaded bait - and even bait scented plastic so apart from dumping out the bodies you never have to touch to rebait (unless you use for a very long time - and by then you'll be over your heeby-geebies hopefully).

 

Both let you bait without any chance of snapping your fingers! 

Housings

If you are setting traps under a house or somewhere the cats are not (or children, if that is a consideration), you can have traps without a cover.  Unless you get your placement just right, these will often fail because rats and mice are cunning, and they will use angles to their advantage.  Always put against a wall if possible - create a wall with some old bricks or wood to direct them at the trap if possible. 

If they are outside or anywhere a pet or child can get them - you must create a cover.  Prebuilt housings are good, and direct the rat into the most vulnerable position.  They can be pricey, when you think about what they are - a bit of precast plastic, or some wood. It can turn a $2 trap into a $30 one...

  

This is the big cheese trap in a purchased trap cover.  I like the see through ones because you can easily check if it needs a reset or body clear.  Always put something heavy on your trap housing - it helps kill the big rats quicker if they can't thrash around with a lightweight trap.

A small mouse trap is basically the same design - although this one makes the mouse come in and turn a corner due to their small size.

But you do not have to buy a housing.  You can make your own like the DOC standard wooden housing (or many variants have online instructions), or just have some wood, bricks etc around your trap.  Anything that protects the trap from paws or fingers (and elements) and directs the rat into the jaws. The simpler it is to check and set your traps, the more likely you are to be successful (and keep kitties paws safe!) 

For a really cheap housing - I bought some small plastic storage boxes - drilled a hole in both ends, taped some insect mesh leftovers on one end.  This lets the smell of the bait out better, AND rats like to see through to the other side (they think they have an escape route and are more likely to go in - rats are actually scared of new things!)  Total cost around $4

  

More Reading 

Jesse Mulligan's Rat 101

Trapping Best Practice - Predator Free NZ

Consumer info on Rat Traps 

BioNet - Pests - Rats