That's a mouse (ETA: sorry, opened the pics larger, looks like a young rat)
Either way, you can get rid of rodents (mice, rats, etc) by placing cotton wool balls soaked in peppermint oil around the areas they like to nest (inside roof, under decks/stairs, in compost heaps etc).
It takes a few weeks but they can't handle the smell and will move off, taking their babies with them (so it's humane).
Poisons are inhumane as they
a) can poison other animals like owls and cats when they eat the poisoned rodent
b) can potentially kill the mom, leaving the babies to starve to death which is terrible
ETA: replace peppermint balls as necessary when they no longer smell strongly.
I run a pet rat club forum and have over 18 years of rat experience