I currently have a notebook in which I keep a record of each animal on their own page. That page includes an id number, description of the animal birth date, family tree, and records of reach litter (number born, date born, colors). Will also include health information and death date as available.
To keep track of reach animal in the racks, I have a piece of foam board on each bin, to which I stick reach animals thumb tack. The thumb tack has the animal's id number and brief description (ie black hood, beige berk, fawn blaze berk). I add the brief description so I can quickly if the animal without having to memorize numbers or refer to the notebook. The thumb tack follows the animal it belongs to, into whichever bin the animal goes. I'll have to get a photo of that doesn't make sense.