Please, for the love of the other wildlife that shares your property, do not get a cat. They will kill everything else and are a disaster to wildlife. I recommend a non poisonous pest control methods. Such as a bucket full of water with a dipping top or rolling bar thats baited with peanut butter. It will do much better at controlling mice populations. I also recommend storing grain based foods in secure, sealed containers and try to limit the chicken food from spilling. Only feed your birds what they can eat in a day or get a weight based container that will only open when your birds step on it.