Keep your garage doors shut! I have had birds in the garage, neighborhood cats, squirrels, wild rabbits, chipmunks! You can also buy a screen that fits a garage door opening. You can order one here and it's quite reasonable: https://www.harborfreight.com/double-garage-screen-door-68310.html
One possible answer is the owl ststue they sell at hunting stores. It intimidated them away for us...crazy right?!
Are there open areas in the eaves? Where are the getting in?
If they're not getting in through the door, as Gk suggested, look for other holes or cracks in the door or walls. You can close those up with expanding foam, sand it down, and then paint it to mach your garage.