Fan for a Half Bath?

Topic: 
Bathrooms
Topic: 
Building Codes
Question: 

I have a downstairs 1/2 bath (toilet and sink only), with an exhaust fan previously installed. I recently had a need to remove the exhaust piping from the fan to the outside vent, due to birds invading the venting...

The bathroom is very small, and does not contain a shower or bathtub. It has also never had a problem with moisture. I am wondering if I really need to have the piping replaced, or if I can simply just cap off the outside vent outlet and be done with the job. Are there any building code considerations here? Is a bathroom exhaust fan really necessary in this case?