WTD: Pied piper

[FD3Si]

Unfortunately, the previous mutual understanding that the vermin that were around the garage and I had has now fallen out of balance.
When I uncovered the nest in my gloriously minimalist and previously very clean engine bay, the gloves were off. They didn't keep their part of the deal, I'm not keeping mine. Rattus norvegicus, we are at war.

However, there are 2 issues - as a staunch animalist I find it very hard to delierately set out to kill stuff, but if I do accept it, it needs to be done humanely.
Also, there are a lot of local cats, and we have chickens.

I've been advised that snap type traps are useful, but the beast can be wary.
Apparently poison is the most effective, however, the way it kills them is completely at odds with my ethos, and I'm concerned about the bodies being consumed by other living things.

Can anyone recommend anything else, or do anything to allay my fears about the dangers of poison?

[sidekickdmr]

You have failed to cover the only type of trap that fits what you want.

One that doesn’t poison or kill the animal, but traps them, alive, check every day, if you have any, chuck in boot and let them go many miles away.

[Martin4x4]

A rescue outside cat from animal shelter which have a hard time homing Semi-ferals. Give it food and a bed in the garage with entrance/exit and your problem will be solved over night in a very natural way.