Sonar strobe groups and buzzes are produced before powered flight is achieved in the juvenile big brown bat, Eptesicus fuscus .

Laryngeally echolocating bats produce a rapid succession of echolocation calls just before landing. These landing buzzes exhibit an increase in call rate and a decrease in call peak frequency and duration relative to pre-buzz calls, and resemble the terminal buzz phase calls of an aerial hawking bat's echolocation attack sequence. Sonar strobe groups (SSGs) are clustered sequences of non-buzz calls whose pulse intervals (Pis) are fairly regular and shorter than the Pls both before and after the cluster, but longer than the Pls of buzz calls. Like buzzes, SSGs are thought to indicate increased auditory attention. We recorded the echolocation calls emitted by juvenile big brown bats (Eptesicus fuscus) over postnatal development from birth to 32 days old, when full flight has normally been achieved, and tested the following hypotheses: (i) buzz production precedes the onset of controlled, powered flight; (ii) the emission of SSGs precedes buzzes and coincides with the onset of fluttering behaviour; and (iii) the onset of flight is attained first by young bats with adult-like wing loadings. We found that E. fuscus pups emitted landing buzzes before they achieved powered flight and produced SSGs several days before emitting landing buzzes. Both observations indicate that the onset of adult-like echolocation behaviour occurs prior to adult-like flight behaviour. Pups that achieved flight first were typically those that also first achieved low, adult-like wing loadings. Our results demonstrate that echolocation and flight develop in parallel but may be temporally offset, such that the sensory system precedes the locomotory system during postnatal ontogeny.