How To Build A Bat House

KATHRYN A. KAHLER

Kathryn A. Kahler is associate editor of Wisconsin Natural Resources magazine.

Looking for a winter activity that is interactive, educational and helps a Wisconsin threatened species? Sharpen your DIY skills with this simple guide for building a single chamber bat house that can attract as many as 50 bats and provide an alternative roost to help maintain the population.

Four of Wisconsin’s eight bat species — little brown, big brown, northern long-eared and eastern pipistrelle — are considered threatened due to white-nose syndrome, a fungal disease that causes extensive mortality in cave-dwelling bats.

WNS, first discovered in New York in 2006, spread across the U.S. and reached Wisconsin in 2014. The disease has caused the most precipitous decline of North American wildlife in recorded history. Hibernation surveys done in winter 2020 showed up to a 97% drop from pre-WNS numbers at some sites and total elimination at other sites where smaller populations had existed.

Bats are mammals and typically have only one or two pups a year, so it can take much longer for populations to recover than for more prolific species like birds. Giving bats a helping hand provides myriad benefits for homeowners and offers advantages on a larger scale as well.

Bats reduce night-flying insects and mosquitoes around your home — including species known to carry West Nile virus — and provide pest control to farmers nationwide. Bats also support the ecosystem as pollinators and plant seed dispersers.

BAT STATS

8: Species of bats recorded in Wisconsin, all either state-threatened or on the "watch" list.

30 years: A bat's potential lifespan. These long-lived mammals usually have only one baby per year, making them susceptible to drastic population decline from causes like white-nose syndrome.

1,000: Number of mosquito-sized insects a single bat can consume in an hour.

$22 billion: Pest control savings per year to North American farmers thanks to bats.

• Box cutter or razor

• 1 piece 26”x24”x”.5 plywood

• 1 piece 32”x24”x.5” plywood

• 1 piece 24”x4”x.5” plywood

• 2 pieces 26”x1.5”x.75” common wood/pine

• 1 piece 20”x1.5”x.75” common wood/pine

• 10 exterior screws, 1-5/8 inch

• Clamps

• Exterior caulk and caulk gun

Step 1: Use a box cutter or razor to score one side of both the front and back pieces of the bat house (26”x24”x.5” and 32”x24”x.5" sheets of plywood). The scored sides of wood will face inward to give the bats a textured surface to roost.

Step 2: Assemble the frame by securing the 20”x”1.5x.75” common wood/pine piece, 1 inch from the top of the 32”x24”x.5” piece of scored plywood, with caulk. Then, secure the two 26”x1.5”x.75” pieces of common wood/pine with caulk to make a horseshoe-shaped frame. This is the inside of the bat house.

Step 3: Apply caulk to the other side of the frame and place the 26”x24”x.5” piece of plywood onto the frame by firmly pressing down. This creates the front of the bat house. The edges of the front and back pieces of wood should align. The top of the front piece should align with the frame.

Step 4: Clamp together the sides of the bat house and drill three evenly spaced (about 8 inches apart) pilot holes through the front piece, framing and into the back piece on both the left and right sides. Ensure your drill bit is smaller than the screw.

Step 5: Align your 24”x4”x.5” roof piece with the top of the framing and clamp to the rest of the house. Drill four evenly spaced (about 5 inches apart) pilot holes through the roof and into the framing.

Step 6: Add some caulk to the ends of your screws. Now clamp down the sides as before and drill in the caulked screws. Repeat this step for the roof.

Step 7: Spread caulk along the front and back of the roof to seal the gaps.

Step 8: After caulk has dried, prime and paint the exterior black.

Step 9: Attach to house or pole 10-15 feet above ground using mounts secured to the back of the box. Make sure there is 1/2” to 3/4” between the box and the mounts using spacers.