Walk toward a squirrel in the yard, and it vanishes up the nearest trunk in a blur of fur. Birds are no braver, lifting off at the first hint of your footsteps. But let wildlife into your attic, and they can comfortably settle in while you go about life one floor below.

And when it comes to shielding your country vacation home against such threats, there’s good news and bad news. The good news: Animals aren’t necessarily more likely to invade when you’re away. “You being home is probably unimportant,” said David Drake, professor of forest and wildlife ecology at the University of Wisconsin-Madison. “They’re not scared by you, and raccoons, mice, squirrels and bats have demonstrated they can get along quite well in high human activity areas.”

The bad news: When you’re away, you’re less likely to detect the early signs of a hostile takeover, especially during colder months or birthing season when mammals and birds are seeking shelter and warmth.…