This is a very effective way to exclude birds, squirrels, raccoons, and roof rats that can cause a lot of damage and personal stress. Squirrels and rats can cause electrical fires due to gnawing electrical wiring and birds can create a mess with bird droppings along with attracting other pests. Not to mention keeping you up at night from all the running around and chatter. If you are a DIY'er be VERY careful if you encounter a gable vent such as this. These electrical wires are HOT. It may be worth a few dollars to let a professional help. I can still remember the old commercials reminding us to keep away from those power lines. Its better to be safe than dead.