Bats can fly in dark because they

Bats are able to fly and navigate in the dark primarily through a biological sonar system known as echolocation [1]. They emit high-frequency sound pulses, typically in the ultrasonic range (above 20 kHz), which are beyond the threshold of human hearing [2]. These ultrasonic waves travel through the air, bounce off objects or prey, and return as echoes to the bat's finely tuned ears [2]. By interpreting the time delay and frequency shifts of these returning echoes, bats can precisely determine the distance, size, and location of obstacles or insects in total darkness [3]. While some bats have functional vision, echolocation is the specialized sensory adaptation that allows them to occupy nocturnal niches and hunt effectively without relying on light. This mechanism is so sophisticated that it enables them to avoid collisions and pinpoint tiny targets like moths during flight [4].

Sources

1. [1] https://en.wikipedia.org/wiki/Animal_echolocation
2. [2] https://www.nps.gov/subjects/bats/echolocation.htm
3. [3] https://www.science.gov/topicpages/b/bat+echolocation+signals
4. [4] https://www.pnas.org/doi/10.1073/pnas.1422843112