Examining the disharmonic distributions of organisms on many islands and frequently finding bats present shows just how capable these creatures are at colonizing new and distant areas. Dispersal areas of the family Vespertilionidae. And though flight is important it not the only trait that gives bats an evolutionary advantage. Through adaptive radiation bats have achieved all sorts of fascinating techniques for eating, sleeping, reproducing, etc. The best known of these is probably the use of echolocation.
Bats have a variety of sight capabilities.
Some have excellent vision while many rely more heavily on their sonar. Look at a bat. If it does, that suggests that it relies heavily upon echolocation. The especially big ears are often used by bats that hover in place to pick off insects that crawl around on trees or on the ground. This is the case with the Hawaiian hoary bat.