As I teach in my bat workshop, don't wear a respirator because of the bats (or any wildlife), instead wear a respirator because of what could have been sprayed in the attic that you'll never know about.
Ideally, you should be protecting your clothing, skin, lungs and eyes which really means wearing a full Tyvek with hood, boot covers, gloves, and a full face respirator at minimum. Of course, this is a double edged sword as you also should have a decontamination and cleaning room so you can clean and dispose of your gear when you exit the attic. I call it a double edged sword as not only does it increase your time and cost for the inspection/work, it also adds a fear component to the work which can then be used in a lawsuit against you (along the lines of the post I made concerning being an expert witness on a histoplasmosis case) should the client become sick later on.
You can get a really good guide on respirators from the CDC at
www.cdc.gov. I believe the booklet is around 80 pages or so and covers everything from dust masks to SCBA. Another good resource is to listen to guys who have been trained/certified for hazmat cleanup to see how they would approach an attic clean out (i.e., testing for lead, copper, zinc dust and asbestos, setting up negative air flow, clean rooms, double bagging disposables, etc.).