A new study in Frontiers in Physiology claims that bats catch insects by sonar because it is far more efficient than using vision, even during twilight.
Bats have eyes and may not have evolved their ultrasonic sonar from the earliest time of their existence on earth. Approximately 1000 species of bats use sonar to detect prey, despite showing considerable variation in the preferred size of their prey and their mode of hunting.
But why? Many bats hunt partly in twilight, similar to insect-eating bird species such as nightjars, which solely rely on eyesight and do fine without echolocation.
Arjan Boonman and colleagues from Tel Aviv University here model the quality of information that two species of bats receive from sonar and eyesight when hunting for insects. The researchers found that both species use their sonar as much in twilight (1 to 10 lux) as in complete darkness.
They show that this reliance on ultrasonic sonar is advantageous, because sonar detects insects (e.g. moths, ant queens, and mosquitos) at distances that are 0.25 to 5 m shorter than eyesight, even under low- and intermediate light intensities. By making it possible to catch small prey more efficiently than with vision only, sonar has opened a unique niche for bats and promoted their astounding diversification.
Article: It's not black or white - on the range of vision and echolocation in echolocating bats, Journal: Frontiers in Physiology, DOI: 10.3389/fphys.2013.00248