Introduction
There are many native mammals that inhabit the Roleystone bush that are mistaken for being Rats. Some of which are accidental visitors to our houses. That being the case we need to distinguish the common rat from the native mammals prior to their disposal.
Using Poisons should be avoided as they will likely to indiscriminately kill native mammals.
This article presents an alternate view of trapping the animal for identification, prior to release or destruction.
Rat Identification
There are two common Rats; they are the Black Rat and the Brown Rat.
The Black Rat
The Black Rat, (Rattus rattus) is an Asian warm climate rodent of subspecies rattus. It is otherwise known as the Asian Black Rat, House Rat, Ship Rat or Roof Rat. The species originated in tropical Asia and spread through the Near East in Roman times before reaching Europe in the 8th Century and spreading with Europeans across the world.
The Black Rat
Despite being called the Black Rat, it comes in several colour forms. It is usually black to light brown in colour with a lighter underside. It is a poorer swimmer, but very agile and a good climber. It is nocturnal and omnivorous, with a preference for grains.
The Black Rat will breed throughout the year, with a female producing three to six litters of up to ten young. Females may regulate their production of offspring during times when food is scarce, throwing as few as only one litter a year. The black rat lives for about 2-3 years, with social groups of up to sixty.
To identify the Black Rat, look for behaviour and general features. The body length of a black rat is typically 135 - 185 mm, with a further 190 - 240 mm of hairless tail. The Rat will have pronounced and bulbous eyes and a rather neurotic behaviour - scrambling to get out.
Black Rat skulls are below.
The Brown Rat
The Brown Rat (Rattus norvegicus) is otherwise known as the Norway Rat. It is a true omnivore and will consume almost anything, but with cereals forming a substantial part of the diet. Martin Schein in his paper "A Preliminary Analysis of Garbage as Food for the Norway Rat" found that the most-liked food of Brown Rats was (in order) scrambled eggs, macaroni and cheese, and cooked corn kernels. Their least-liked food was raw beets, peaches, and raw celery.
The Brown Rat
The Brown Rat is usually active at night and are good swimmers, both on the surface and underwater. Unlike the related Black Rat, the Browns are poor climbers. They dig well, and often excavate extensive burrow systems.
To identify a Brown Rat, look for coarse fur, usually brown or dark grey. The underparts are lighter grey or brown. The body length of an Adult can vary from 175 - 260 mm, The tail can be 150 - 215 mm (approximately 80% shorter than the body length). Adult body weight averages 350 g in males and about 250 g in females, but a very large individual can reach 500 g. Their vision is poor, they are unable to detect colour and are blind to long-wave light.
The Brown Rat can breed throughout the year if conditions are suitable, a female producing up to five litters a year. The gestation period is only 21-23 days and litters can number up to fourteen, although seven is common.
Brown Rat Skulls are below.
For more information on identification of rats and commonly mistaken natives, visit http://australianmuseum.net.au/Is-it-a-Rat
Traps
The general idea of Trapping is to dispose the rodents rats you find, and release the other creatures a hundred metres or more from your house. One way to dispose the rodents is to drop the trap into a bucket of water.
The two figures below show a home made trap.
Bill's rat trap - set
Bill's rat trap - sprung
The main body is ½ inch (12mm) square galvanised wire mesh. In cutting the wire mesh, make it a little big so you can make ‘tags' on the outside of the mesh; they are bent to complete the joints. Besides the wire mesh you will need a few bits of stiff galvanised wire, a few pieces of 0.4mm galvanised steel sheet and, perhaps, some heavier wire for the door slider and sliding mechanism. Of course, you will need some good holding and bending pliers. The flat broad ‘wire twisting' pliers are good, with the parallel grasp and a smaller pair to make the bends with precision.
The spring is made from a hardened wire bristle from a streetsweeper, which can commonly be found lying in the road; the flat wire is most easily bent with loops on its end by wrapping it around a nail in a vice.
With this design, an old shoe rack was cut up with a hacksaw; when the pieces were bent they made a perfect locking slide for the door as well as a balance arm for the door.
This design works when the food is snatched or simply eaten by the rat. The movement of the food sets off the hair trigger which releases the door latch. The angle of the hook determines whether pulling is necessary or simply bait removal (eating). When the door rotates to close, the slider falls in to lock the door in place.
In about two months, 5 rats were caught with this trap and one native. Make a ‘comfey' little surround for the trap that does not hinder the mechanism and, in a night or two, you will catch a rat (provided there is a rat around). Note that there is never just one rat as they act in groups.
An alternate design, by Mike Green, uses a platform. It is roughly the same size (about 30 cm long, 9 cm wide and 9 cm high) but is mounted on a heavy wooden stand to give stability.
Mike's rat trap - set
Mike's rat trap - sprung
The platform is a flat piece of 0.4 mm galvanised steel sheet supported by a heavy wire hook through a single hole. The other end of the heavy wire hooks into a triangular piece of double sheet metal which acts as a fulcrum. With the fulcrum properly placed, the weight of the rat causes the platform to fall. Another heavy wire lying along the top of the trap is attached to the other side of the fulcrum; a loop in the wire forms the trigger for the trap. The door has the shape of a paddle with a long tab on the top. The loop in the heavy wire is set to just hold the door up. The result is that the weight of the rat entering the trap triggers the door to fall; a long, heavy ‘U' shaped wire acts as a sliding lock. Note that a small bend at the bottom of the door keeps the ‘U' shaped lock from falling too far. The trap works on gravity, without a spring.
For those who are not so handy with construction, the Roleystone Hardware also has live traps for mice and rats.
The type of bait you use needs to be something the rats prefer. Pieces of apple work well, having only caught one ‘non-rat'. Four rats have also been caught with fig.
Importantly, when using traps you should check them regularly - at least once a day. On occasion, native animals will also be trapped, so you will need the free them. On cold mornings, exposed traps can freeze their captives if left in an exposed trap for too long (particularly young bandicoots).
To reduce the likelihood of capturing bandicoots, keep the trap a foot or more off the ground. The Rats should still jump up, where the bandicoots are more likely to stay on the ground.