A common item found on roofs are attic fan vents. A common area we find critters entering properties are through those vents. Attic vents are generally larger than most box vents and tend to be circular. Their purpose is to help move heat and vapor out of the attic space and away from the roof. In order to install them into a roofing system a large hole must be cut into the roof decking so they can aid with ventilation. This large hole with an attic fan over it can allow for critters to enter your home if not protected.
In order to exclude critters from an attic fan vent and still allow for it to function, breathable meshing should be used. Some people cut pieces of hardware cloth and secure a circle around the vents hood to the shingles. Others simply purchase a prefabricated breathable vent cap and secure it to their roof. These barriers of protection will allow for the roof to breath with the attic fan and prevent critters from entering.