I have at least 20 bats living behind some soffit next to a chimney on our house. I can see where they're going in and out. My first thought was to go up there with a headlamp after dark and try to caulk the gap while they're out hunting, but I wouldn't mind having a pro come out to look at it. Does anyone have a recommendation? Sauk county in SW WI. Thanks!

No recommendation as I don't know anyone in that area but I would advise against just caulking at night as they may not all fly every night and there may still be juveniles inside. Also the rest of the structure needs inspected and any other possible entry points addressed as well to prevent them from just going around the corner and back in.

We are still in the blackout period here for a couple more weeks when we are prohibited from doing exclusions due to possible juveniles.

The best approach once it's determined that juveniles arent present or old enough to fly is a one way bat valve after addressing all other potential entry points. Leave the one way in place long enough for all to exit, week to ten, then seal it up. Consider using good quality sealants for long term service and if chewing species like rats or squirrels are possible step up to metal flashing.

In WI we are prohibited from removing bats from June 1st to August 15th. You have some time to work up your plan and then activate it as the fall when temps are above 50 F the bats are active and more likely to all be out while hunting.

Bryce

Nobody does the bucket of water thing anymore. I remember my grandpa doing this all the time on the old farm house

Incorrect. The non-exclusion dates for excluding bats in Wisconsin was shortened to 6/1 - 7/31.

Remembered one. Paul Winklemann is a member on here and this is his family outfit.

https://advancedwildlifecontrol.com/about-us/

Depending on your house, I could probably walk you through what you need done
Just send me a pm.

Thanks for the advice and recommendations. I'll follow up on these leads. With our mosquito problem, sometimes I feel like i should open up a few more gaps to let more of those critters in!

You might consider erecting a bat house or two. Bats are definitely good to have close to home, but not too close like in the walls haha