Personally I think rats are one of the coolest animals ever. Incredibly intelligent, adaptive and tenacious. But, if you are over run you may need to consider some sort of extermination process.
I would NOT, without calling in a professional, put our poison on my own. You risk secondary poisoning of neighborhood animals that may find and consume the dead rats.
The odds of them running into your home are minimal, they are after the blackberries and once this food source is depleted for the season they will move on to other food sources.
If they are not causing damage to your home in any way I say live and let live.
I live in rattlesnake country, just this morning my neighbor who was out walking her dog ran up to my car at the the corner of my road and pointed out a dead young rattler on the side of the road, most likely run over.
She was all panicky and hyped up over this dead snake in the road….jeez, calm down! lol
I have encountered 4 rattlesnakes in 18 years…no big whoop.
I guess I am just not prone to demonizing nature unless it is seriously invading my space.