Researchers from the University of Southern Denmark have just completed a new study into the communication of Sperm Whales. Through listening to the characteristic tapping sounds (known as codas) of 7 sperm whales in the waters off the Azores, the team discovered that these sounds serve as a form of communication between individuals.
This discovery is significant as prior to this study, biologists believed that sperm whales only communicate as a single group, i.e. that each group has their own set of vocalisations used by its members to communicate with other groups.
“What we discovered, however, was that individual sperm whales communicate individual messages to other individual members of the group,” said Magnus Wahlberg, Associate Professor, Institute of Biology, University of Southern Denmark.
The sperm whale is the largest odontocete, or toothed whale, growing as long 67 ft (20.5 m) and weighing up to 57,000 kilograms . They are the deepest divers of the great whales and can descend to depths of over 5,000 feet (1500 m) and stay submerged for over an hour. Average dives are 30-50 minutes long to a depth of 980-1,970 feet (300-600 m). Sperm whales live in close-knit societies. They are raised by matriarchal units that can include three generations. The vocalisation of sperm whales is achieved via a form of echolocation and has been extensively studied.
When echolocating, the sperm whale emits a directionally focused beam of broadband clicks. Clicks are generated by forcing air through a pair of phonic lips at the front end of the nose, just below the blowhole. The sound then travels backwards along the length of the nose through the spermaceti organ. Most of the sound energy is then reflected off the frontal sac at the cranium and into the melon, whose lens-like structure focuses it. Some of the sound will reflect back into the spermaceti organ and back towards the front of the whale’s nose, where it will be reflected through the spermaceti organ a third time. This back and forth reflection which happens on the scale of a few milliseconds creates a multi-pulse click structure.
When these clicks are viewed on a spectrogram, a visual representation of an audio signal, each reveals a remarkably complex pattern. Inside these clicks are a series of shorter clicks, each lasting a few thousandths of a second, and so on. Each individual sperm whale is capable of vocalising a variety of messages, some of which they use more frequently than others. It appears that geographically separate pods exhibit distinct dialects.
The team’s research in this study was achieved through the attachment of listening instruments to seven sperm whales, through which the team subsequently attempted to analyse the whales’ codas. These codas work in a similar way to morse code, with messages consisting of a series of tapping sounds in a variety of combinations, such as four long taps followed by two short ones. The scientists registered 21 different messages.
“One could imagine that the vocalisations give information about who each of the individuals in the group are, whether they are heading for the surface or depths or if they have found food. It could be mothers calling to their young or females inviting males to mate with them.”
In total they recorded 802 of these vocalisations from five of the whales, while the remaining two stayed quiet. Colleagues from Aarhus University and the University of the Azores accompanied the researchers on the trip.