Question

We have 2 female rats(mother & daugher) that are about 1 1/2 Y/O in a 3 a large 3 story cage. They are usually at my roommate's 3rd grade classroom, but they have been at home for the summer. The daughter runs on the wheel in the cage a lot. Lately, the mother has started to "nip" the daughter either behind the ears, or on her behind, until she whimmers. The daughter is loosing some of the hair behind her ears. The mother, sometimes chases her tail, rolling down the stairways to the cage floor. I have put the mother in another cage and her behavior improves for awhile (no "nipping'), but then reverts. My roommate then blocked off 1 of the stairways, essentially dividing the cage in 1/2, each w/ their respective food/ H2O. The mother chewed a wooden ladder (a toy) in half. I know this is stress behavior, but any suggestions on what I could do to decrease the rat's stress, or improve their quality of life?