SIGNAL STRENGTH, TIMING, AND SELF-DEAFENING - THE EVOLUTION OF ECHOLOCATION IN BATS

We propose that the ancestors of bats were small, nocturnal, sylvatic gliders that used echolocation for general orientation. Their echoloca tion calls were short, low intensify, broadband clicks, which translat ed into a very short operational range. In the lineage that gave rise to bats, a switch to stronger, tonal signals permitted the use of echo location to detect, track, and assess flying insects in subcanopy sett ings. We propose that these animals hunted from perches and used echol ocation to detect, track, and assess flying insects, which they attack ed while gliding. In this way, the perfection of echolocation for hunt ing preceded the appearance of napping night, which marked the emergen ce of bats. Flapping night had appeared by the Eocene when at least ei ght families are known from the fossil record. Stronger signals and ad aptations to minimize self-deafening were central to the perfection of echolocation for locating flying prey. Echolocation constituted a key innovation that permitted the evolution and radiation of bats. At the same time, however, its short effective range imposed a major constra int on the size of bats. This constraint is associated with flight spe ed and the very small time intervals from detection of, and contact wi th a flying target. Gleaning and high duty cycle echolocation are two derived approaches to hunting prey in cluttered situations, places whe re echoes from background and other objects arrive before or at the sa me time as echoes from prey. Both had appeared by the Eocene.