Neuroscientist James Simmons of Brown University and his co-workers followed the night-time hunting sorties of big brown bats (Eptesicus fuscus) during summer evenings in Providence, Rhode Island, using infrared thermal imaging cameras and ultrasound detectors1. What they saw overturns standard views about the nocturnal gymnastics of these creatures.

Bats plucked beetles from mid-air as the insects rose from the grass. Some bats would even plunge into bushes to capture their prey. Using reflected sound waves to pounce on an insect buzzing in the night air seems tough enough. But imagine trying this when the insect is perched on the leaf of a bush, with the sound waves bouncing back from all the other leaves.

When they do this, bats seem to reduce their sonar squeals. Perhaps this is to avoid too many confusing echoes from the vegetation, or just to conceal their approach from the beetles. Nevertheless, in such situations "the overlapping echoes would have to be separated by their arrival times and directions for the bat to perceive the objects individually", say the researchers.

The bats also used sonar while flying low over water to take a drink, or to capture prey from the ground. They displayed some of their most adroit manoeuvring in dramatic 'dogfights', in which one bat pursued another. "The scope of echo processing needed to guide bats through these high-speed aerial dogfights … is a positive embarrassment for most current thinking about auditory coding of echoes," say the researchers.

An understanding of how bats perform these feats could produce technological spin-offs for sonar navigation and detection equipment, Simmons' group suggests. Already bats' broad-band (many-frequency) sonar system is emulated in mine-sweeping technology.

Because bats fly by night, it difficult to watch them do it. Usually they can be spotted only when silhouetted against the evening sky. Once they come close to ground or vegetation, they become all but invisible.

As a result, most studies have focused on bats hunting for prey in the open. This has led to a belief that, whereas brown bats use echolocation to find and capture prey in the open, their sonar systems can't cope with more complicated acoustic environments.

Now hypotheses about how bats process echolocating signals "will have to be revised to accommodate the higher acuities implied by the bat's successful completion of [these] complex acoustic tasks," say the team.