He's cute and enjoying your hospitality. One reason to get a flue cap.
How often should I have my chimney swept? The simple answer is: The National Fire Protection Association Standard 211 says, "Chimneys, fireplaces, and vents shall be inspected at least once a year for soundness, freedom from deposits, and correct clearances. Cleaning, maintenance, and repairs shall be done if necessary." This is the national safety standard and is the correct way to approach the problem. It takes into account the fact that even if you don't use your chimney much, animals may build nests in the flue or there may be other types of deterioration that could make the chimney unsafe to use.
The National Fire Protection Association recommends annual chimney inspections, and cleaned when needed; your approach should be based on usage." So if you use your flue more frequently you might need to have your chimney swept more than once a year. The Chimney Sweep Guild of America recommends to have the chimney swept out after a cord or cord and a half is burnt.