Killing rats just creates space for other animals to move in. 
Rats are intelligent, social, and emotional animals, and killing them is not humane. Toxic baits, which are often used to kill rats, can cause slow and painful deaths. The bodies of poisoned rats can also be dangerous to other animals that eat them.

Never use glue traps, which have been banned in several countries for their extreme cruelty, and bear in mind that rat poison can kill other wild animals, such as foxes, owls and hawks.