Legal Question in Landlord & Tenant Law in California

You are obligated to provided a rodent proof living structure. If the mice managed to get into the walls, unless you can establish that the tenants let them in through windows or doors, you are responsible for the extermination (and closing up entry points). I had a similar problem but was able to establish that my tenant left the back door open for their dog and and dog food on the interior back porch, in order to prevail on deducting extermination charges from their deposit. In the process, however, I got well versed on the law on this issue. If the structure has entry points (which for a mouse can be as small as a nickel, and for rats a quarter) other than normal doors and windows that properly seal when closed, you are on the hook for rodent entry. Same is true if they are IN the roof. Wild animals ON the roof can't be eliminated anyway, so they are not your problem.