Exterior openings are not only attractive to animals but they are also energy-robbing outlets. When gutter cleaning and limb-trimming, take the time to look at your house through the eyes of wildlife.
Before taking action, however, make absolutely sure there are no animals already inside. Stuff holes loosely with a paper towel. If after three days the paper stays in place, you can safely close up. Use caulk for small holes, staple or screw hardware cloth over larger holes or make permanent repairs.
Inspect for potential entry points where pipes, vents and cables exit the house. Window wells, exhaust vents, brick and siding gaps can all be potential entry points. Small openings can be caulked, stuffed with copper mesh or filled with expandable foam. Larger openings should be repaired to original condition.
Look for droppings, chewing and nesting material. If a hole is found, assume an animal is present and NEVER seal it up until you are completely sure that all animals are gone. To inspect, turn off any attic lights and look for outside light leaking in. Openings, like exhaust vents, are often covered with bug screen that small animals can work through.
Take caution when it comes to bats. Look carefully for quarter-inch pellets that are a bit shiny and friable. Call a bat removal specialist if you suspect these animals are using the attic.
Check inside by shining a light up the flue looking for animal signs on the damper and smoke shelf. Also check the chimney flue from the roof to make sure no animals are present and install an animal-proof chimney cap.
Look for loose vent screens, warped siding and trim board that is deteriorated and pulled away. Make permanent repairs once you have completed the attic inspection.
More information at Humane Wildlife Services.