I replaced 4 plastic roof vents on this job, homeowner had complained of squirrels in the attic eating thru a vent. When I went up on the roof I saw 4 vents that were eaten clear thru by squirrels who then made a home out of her attic.

One squirrel didn't make it and got stuck and died in the vent itself, though this is gruesome, it's a lesson to not use plastic vents on your roof where squirrels are present. I replaced all the plastic roof vents with metal ones. Plastic vents also have a short shelf life on the roof, cracking due to heat and UV and then create a leak problem. Call or email if you need your plastic roof vents replaced (in the Portland, Oregon area).