Cold weather months bring more “wild” visitors into structures. Sometimes inspection of access/entry points being used are obvious, but sometimes they are not. When you have multiple openings where animals could be getting in, determining the right ones in which to install one-way doors or traps may be questionable.
One simple and effective tool to determine where an animal is entering and exiting an opening is known in the industry as a “soft plug.” I recommend using wrapping tissue paper — yep, the same stuff you use during the holidays on the inside of boxes to wrap clothing items. It’s light and inexpensive, and can be crinkled into an appropriate shape/size to stuff in a hole. Yet it’s light enough for animals to either push or pull out to gain entry.
When the tissue is disturbed, you know for sure that is an opening being used — and you know exactly where to set your trap or exclusion device. You can use any type of lightweight paper material, of course; you just want it to be easily removed by an animal.