The synchronisation of signal emission with wingbeat during the approach phase in soprano pipistrelles (Pipistrellus pygmaeus)

Previous studies have shown that, during search flight in bats, wingbeat, r espiration and echolocation are synchronised in a 1:1. relationship. An eff iciently integrated locomotor-respiratory system enables bats to produce in tense echolocation signals at little or no cost above that required for fli ght, In this study, we investigated the coupling of wingbeat with echolocat ion in the laboratory during approach flight in soprano pipistrelles (Pipis trellus pygmaeus) using high-speed digital video at 250 and 500 frames s(-1 ). We found that soprano pipistrelles most commonly produce single or doubl e pulses per wingbeat, Single pulses per wingbeat occurred in two alternati ve positions: immediately before the end of the upstroke or after the start of the downstroke. Double pulses per wingbeat were emitted in the same win gbeat positions on the upstroke and the downstroke, as in single pulses per wingbeat, We suggest that, during approach flight, the coupling of more th an one echolocation signal with a single wingbeat and expiratory cycle allo ws echolocation to remain energetically economic. When soprano pipistrelles approached a Perspex disc target, an increase in mean repetition rate was achieved by producing an extra pulse per wingbeat, Finally, we hypothesise that the bat's approach to potentially interesting targets in the same hori zontal plane as it's flight path, i.e. during flapping flight, may be chara cterised by the production of double pulses per wingbeat, resulting in a un ique pattern of echolocation pulse intervals.