Look for some traps at your local garden store. Squirrels are tough to get rid of, and you might be dealing with more than just one. If you don't want to kill it, use baited traps. You have to check the traps every day though. Another way would be to get a cat, but the cat will get rid of the birds.
If you do decide to kill it, try using a pellet gun or some sort of air rifle. Poisoning the little guys puts more animals at risk than just the squirrels. Birds can go after the poisoned food. Neighborhood cats can find a dying squirrel easy prey, as can wild carnivores such as hawks, owls, foxes, etc. If you poison the animals that are supposed to keep the squirrel population in check, you will end up having an even worse problem in later seasons.
Ryan