Rats will take food wherever they can get it, so it's really up to you to decide whether you're OK about them in the garden. If you don't, you can phone the rat-catcher. If you're happy about them at the end of the garden, then keep things clean near the house, so that there's nothing for them there.
You can take away their hiding places, for instance by not storing things untidily. Don't put too much bird food out at once, so there is more chance of the birds finishing it all up without dropping it everywhere. Grains and seeds are among rats' favourite food.