The important thing is that rats are nocturnal for the most part, and chipmunks are out in the daytime exclusively. So if you can put out traps at night, and whisk them in first thing in the morning you should catch only rats. Baiting with peanut butter works really well for us. I'm a night owl, and put the traps out when it gets dark, about 8pm here. Then I collect them before I go to sleep at midnight if my husband is out of town - he's the early riser of the two of us. Still, I do catch a rat or two most nights. They come to our bird feeders . . doesn't everybody??
Yes, please don't put out poison unless you can be sure to contain the poisoned rats! My daughter's cat ate a poisoned mouse and almost died - twice! We still can't find out who is putting out the poison but it's sure an irresponsible way to go about getting rid of rats. Her cats are now confined to indoors, sadly.
