Pet Female Rat

Question
QUESTION: Hi. We have 3 female rats all sisters at age of 6 1/2 months. 1 of them keeps falling off the solid shelf in their cage (Jenny cage). She then crys, but I can't see anything wrong with her. Is there any reason for this.

ANSWER: She may have a neurological issue - an inner ear imbalance - vertigo - her siblings pushing her off for dominance - seizures? It really could be just about anything. Is she tilting, swaying when walking, acting any differently than usual?

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QUESTION: Her sisters are nowhere near her when she falls. She doesn't seem to be acting any different and she's still climbing up the bars okay

Answer
Without having any other symptoms, it could just be the case of a rare but clumsy rat or a case of missing depth perception - eyesight troubles - lending to her imbalance. I really wish I could help more; but there isn't much to go off here.. is there any way for you to lower her shelves/ramps or set up fall breaks to prevent her from hurting herself when/if she falls?