Wildlife Exclusion and Animal Proofing in Michigan

Where do animals get into a Michigan house?

The National Park Service’s rodent exclusion manual gives a checklist: siding, eaves, soffits, gables, porches, chimney clean-out ports and every place a utility line or pipe passes through a wall, foundation or roof. The approach to the roof matters too. The manual says to remove limbs that overhang the roof or come within six feet of it, trim trees and shrubs 18 to 24 inches back from the building, cap chimneys and screen vent pipes with quarter-inch mesh. For raccoons, the CDC adds closing off access to attics, basements and crawl spaces and clearing trees away from the roof line.

Size is the hard part. The CDC and the U.S. Forest Service both say bats can get through openings as small as a quarter inch. The National Park Service puts the gap a mouse needs at a quarter inch, about the width of a pencil, and a rat at half an inch. For bats, the CDC’s advice is to watch where they leave at dusk, which may show how they are getting in.

How do one-way doors work?

A one-way door, or exclusion device, goes over an opening an animal is using. It lets the animal out and stops it getting back in. For bats, USFWS describes one-way bat tubes that allow bats out but not back in, and the U.S. Forest Service puts the rule the same way: bats should be allowed to leave the roost but prevented from getting back in, and the openings closed when they are gone.

Timing decides whether a one-way door is safe to use. For bats, USFWS says exclusion should never happen during the maternity season, typically May 15 to August 15, and the National Park Service explains why: evicted mothers may abandon young that cannot yet fly, and the pups can starve. USFWS also says bats found hibernating in winter should be left where they are until spring.

For squirrels and raccoons, the question is young in the nest. U.S. Forest Service species data put most fox squirrel births in mid-March and July, and raccoon mating from January to March. Ask the operator how they check for young before the last opening is closed.

For birds, it depends on the species. USFWS lists the European starling, house sparrow and rock pigeon among the non-native birds the federal Migratory Bird Treaty Act does not cover. A nest with eggs or young in it, from a bird the Act protects, needs federal authorization to remove, while an inactive one can be destroyed without a permit as long as no one keeps it. States can still protect non-native birds, so ask the operator which state permits cover the work.

Once the animals are out, the door comes down and that last opening is sealed like the rest.

What materials keep animals out?

Durable ones, and the metal matters. The National Park Service’s rodent exclusion manual recommends galvanized sheet metal of 24-gauge or heavier for most rodent work, and notes that mice, rats and squirrels can gnaw through aluminum; aluminum coil keeps out bats and most birds (not woodpeckers), but not rodents. Hardware cloth screens vents and open pipes, and concrete or mortar closes foundation cracks. Steel wool is a weak fix: the manual notes it is flammable, rusts and lets rodents work their way around it, and it prohibits its use. Vents need a screen rather than a solid seal so they still do their job.

For the animal-specific details, see mouse and rat removal for the gaps small rodents use and bird removal for vents and soffits.

Why do animals keep coming back to the same house?

Because the way in is still there. USFWS says the large groups of bats found in warm months are almost always pregnant and nursing females that return to the same colony year after year. For rodents, the National Park Service notes that they start looking for a way into buildings as the weather turns cold, and that exclusion is never permanent, so it recommends checking the outside of a building twice a year, in spring and in fall. An attic with a way in is a standing offer.

Food nearby makes it easier. For mice and rats, the EPA advises removing food, water and shelter, feeding outdoor birds only huskless seed or not at all while an infestation is being dealt with, and turning compost piles to cover new food scraps. For raccoons, the CDC advises cutting off food and water and keeping trash in tightly closed containers, and notes that food left out for cats can draw them in.

Ask on the call what the quote covers; the guide to what sets the price explains how the parts fit together.