All of the Mouse-sized micro Bats use ultrasound calls for echolocation but fruitbats and flying foxes (megabats) have lost this ability. Although we can’t hear it, echolocation requires bats to scream at 130 decibels! That takes a lot of energy but the micro Bats are able to harness some of the muscular efforts from their wingbeats to generate the air pressures needed for their ultrasound calls. mega Bats flap their wings too slowly for this to work and considering that flying is already more tiring for them because they are heavier, it makes echolocation too exhausting to be worth it.