One summer, yes, hence the nickname.

We had a BAD infestation in our little 4 block neighborhood. The city killed 6 and they gave me permission (cause I work for the sheriff's department and was a police officer in town for 3 years) to use my pellet gun, an RWS Diana model 45 .177. I killed 9 or 10 in about a month to a month and a half if I remember correctly and it could have been as many as a dozen over the course of a year.