About Warren chickens, this was taken from a UK forum site:
The ISA Brown or ISA Warren - is a hybrid chook - a combination of pure breeds, bred together for a specific purpose. As far as I know, Warrens are what you and I would know and recognise as birds used as battery hens.
They are a lovely docile medium brown/ginger bird and an excellent layer - bred for maximum egg production. They are ideally suited for free range conditions, and for small gardens and you should get approximately 325 brown eggs per year.
Warens are a very people friendly docile bird, ideal for the first timer and for people with children. They love interaction with us humans and we've had great fun with them. You will always have company if you start digging in the garden with a Warren.......they appear from no-where and literally sit on the shovel waiting for a worm!