Legal Question in Landlord & Tenant Law in California

I'm afraid the only true answer is "it depends." What it depends on is how long they have been there and how they got in. I am up on this issue because I had tenants who kept a dish of dog food just inside the back door, and left the back door open whenever the dog was outside. The back porch could be sealed from the rest of the house, but not the basement. It wasn't long before rats began living in the basement for easy access to the dog food, and eventually they nested under the range in the kitchen, since the door to the porch and basement was left open when the back door was closed. When the tenants stopped paying rent and tried to defend on the basis of uninhabitability, they lost big time. In your case, after only two weeks, chances are good it's the landlord's responsibility, but not absolutely. For a single family dwelling, the landlord must provide an exterior that is not only sealed against the weather, but also vermin (in apartment buildings the units must also be secured from vermin entering from common areas). Once the landlord delivers a sealed and vermin free house, however, the burden shifts to the tenants. If the tenants do not keep doors, windows, crawl-space or basement access, etc. closed, and the interior free from rodent attracting things such as food and nesting materials, the tenants must pay for extermination. So take a look at the facts of your particular situation, make sure you didn't inadvertently let the rats in, and assuming you did not, then make the landlord pay.