Ontogeny of Echolocation

What is ontogeny you ask? Ontogeny is the development of a behavior in an individual from its conception to its fully developed or adult state. Wikipedia: Ontogeny

While timelines vary slightly amongst different families of microbats, practically all follow a developmental process of:

  1. Birth without ultrasounds.
  2. Postnatal concurrent development of auditory and vocal systems leading to development of skills and modification of frequency.
  3. Stereotyped adult state.

Birth:

At birth, microbats do not posess the abilitity to emit the ultrasounds necessary for echolocation. Most are born blind and deaf, but are able to emit vocval calls in frequencies audible to the human ear. These calls are brief and harmonically structured.

dogbat mother
Above: A dogbat mother shelters her newborn baby. When removed from its mother the baby will emit an 'isolation call' in the audible frequency range.

Postnatal Development:

From the second to the fifth postnatal week, juveniles undergo a rabid development of the auditory midbrain which leads to a rapid increase in the threshold sensitivity of the ear.

Above: Spectra (bottom) and Sonograms (top) of and isolation call (A) and echolocation calls (B&C) in juvenile horseshoe bats. Note decreasing duration and increasing frequency.

As the juveniles age to weeks two and three, they begin nasal emission of echolocation calls that are up to 15khz lower than the calls of adults. The frequency of their calls increases by about 1 khz/day until they reach the adult frequency range. As the vocal capacity for increased frequency develops, the auditory midbrain becomes increasingly fine tuned to the call of the individual.

Most juvenile bats begin to fly around 4 weeks of age. As they learn to fly, the juveniles learn to coordinate their flight with echolocational navigation skills. This postnatal period of 2-5 weeks seems to be a critical period of learning, as bats exposed to an environment in which the echoes of their calls were distorted during this time show a decreased aptitude in obstacle avoidance.

it is in the fourth and fifth weeks of development that the more sophisticated auditory mechanisms such as Doppler shift compensation emerge with the maturation of the auditory midbrain.

Maturity:

After about five weeks of age, the echolocational behavior of most microbats has reached full maturity. The frequencies of these mature echolocational calls very greatly depending upon the environment, but call Hz are not neccessarily species specific identifying characteristics as there is overlap between species.