Dot,
The easy way to tell the Native Rat from Rattus Rattus (Norwegian Black Rat) is the Native one has a pear-shaped body and a fat tail which tapers. The Norwegian has an ovoid body and the tail is just about uniform thickness for its full length.
(Info from Park Ranger at SA Native Rat Sanctuary/Breeding Project.)
Re: rat baits.
DO NOT use them in open spaces!!!
I tried to bury one under an ornamental pond in our yard. Shoved it down a mouse-hole. In the time it took me to turn around & grab the hose to refill the pond our Beagle had dislodged the fibreglass pond, dug out the poison tablet & bolted with it. Our Lab decided he wanted some of this prize, & bit half of it out of Beagle's mouth.
Net cost @ vet's: $800! (Stomach pumping & antidote injections - by two!)
Traps are safer, but monitor them
daily for unintended by-catch of wildlife.