As of the new changes to bat spawning, bats can be found frequently in woodland mansions. During nighttime, they also spawn commonly under trees, even ones with the smallest canopies.

To reproduce:

1. Locate a biome with many trees.
2. Use the following commands:

   /time set night

   /effect give @e[type=bat] minecraft:glowing 60

1. Notice that bats are spawning on the surface, beneath trees and often with no caves nearby.