Whales 'communicate by slapping water in noisy conditions'

An international team, led by Sydney University, has based its findings on an analysis of humpback whales during their southern migration off a beach about 150 km north of the Australian city of Brisbane. Team member Professor Doug Cato said: "As far as we are aware, there have been no studies to date on any animal species which demonstrate the replacement or enhancement of an acoustic signal with another type of signalling behaviour when background noise increases.

"Our study showed that humpback whales gradually switched from primarily vocal to primarily surface generated communication when faced with increasing wind speeds and background noise levels, but kept both methods of communicating in their repertoire." The study found that the whales' surface-generated signalling included surface behaviours such as breaching or slapping of the tail fins or pectoral fins -- and the noisier the ocean became because of rough weather, the more they used fin slaps and breaching, rather than song, to communicate.

"Vocal signals have the advantage of having higher information content but may have the disadvantage of losing this information in a noisy environment. "Surface generated sounds have energy distributed over a greater frequency range and may be less likely to become confused in periods of high wind-generated noise but have less information content when compared with vocal sounds.

"Therefore, surface-generated sounds may improve detection or enhance the perception of vocal signals in a noisy environment," Prof Cato said. The findings have been published in the 'Proceedings of the Royal Society' journal.