The ability to heat and emit the ultrasounds necessary for echolocation is not present at birth in the pallid bat and does not appear until at least a week postnatally. Dramatic changes occur both in pulse structure and auditory tuning as the bat matures. Pallid bats begin to fly at four weeks of age, but continue to nurse until seven weeks old. This allows them time to coordinate the flight and echolocation skills necessary for survival. Bats learn to correlate outgoing pulse with returning echoes. Naive bats approaching an obstacle do not exhibit the expected increase in pulse repetition rate, which occurs after some experience. The normal development of echolocation skills as judged by obstacle avoidance can be correlated with sound emission. Deficits occur in bats raised in environments in which their echoes are distorted or attenuated.