(Planet Earth Online)
Sperm whales share patterned clicks to communicate
11 January 2011, by Tamera Jones
Sperm whales communicate with other members of their pod using a handful of patterned clicks which all individuals in the group share, researchers have found.
Sperm whale.
All whales in a pod use the same small selection of patterned clicks. Scientists think the animals use the sounds to show other whales in the pod that they're part of the same gang.
But the researchers found that a female which had recently given birth to a calf used a completely different pattern of clicks.
'This female is probably identifying herself to her calf so that the calf can find her,' says Dr Luke Rendell from the University of St Andrews, lead author of the report, published in Marine Mammal Science.
'The nursing female probably has to balance her need to identify with the group and her need to identify with her calf,' he explains.
The researchers found that the set of patterned clicks this mother used was subtley different to the other clicks they recorded. 'The coda she used dropped one click off the end. It's not that easy to tell the difference, but it's probably clear to these animals. It was a surprise to find this difference.'
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Sperm whales exchanging patterned clicks called codas.
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This is the first time researchers have been able to say that sperm whales (Physeter macrocephalus) definitely share a repertoire of sets of patterned clicks, called codas.
Sperm whales hold many records: they're the deepest diving mammal, the largest toothed whale and have the biggest brain on Earth. But they don't have the sharpest eyesight or sense of smell. So they communicate using codas, which can be incredibly loud. The sounds are very different to the sounds made by other marine mammals like humpback whales, which sing haunting songs to each other, or dolphins which whistle.
The whales make the sounds in the 'big tub of oil at the front of their huge heads', explains Rendell. Along with air sacs in the whales' heads, the structure produces multiple pulses, just fractions of a second apart.
LISTEN
Sperm whales exchanging patterned clicks called codas.
Download (mp3, 518 KB)
Click the play button above to listen now
Until now, some researchers thought that each sperm whale might have its own individually distinct coda pattern, which it used to identify itself to others.
But these latest findings suggest that sperm whales don't use individual codas to identify themselves to their group. Instead they may use their clicks to communicate that they belong to a particular pod, and to maintain social bonds.
Sperm whale pods are made up of females – with a few young – and average around 12 individuals. Male sperm whales leave the pod when they're juveniles and join all-male pods for a few years, before living a solitary life roaming the oceans.
Rendell and colleagues from Dalhousie University, Canada, recorded the codas while studying a pod of seven sperm whales in a sheltered spot downwind of Dominica over 41 days. The whales had been individually identified in a previous study, so the researchers could assign codas to individuals.
'Normally sperm whales are fairly nomadic, travelling hundreds of miles across the open ocean to feed on squid. So it was really unusual to see these whales congregating in such a small area,' says Rendell.
They had to use sophisticated signal processing software to measure the tiny interval between the pulses in the whales' codas. 'If two clicks have different intervals, we know that they're from two different animals,' says Rendell.
Sperm whales regularly dive to depths of over 800 metres in search of their squid prey. They have collapsible lungs to allow them to cope with the pressure at these depths.
Young sperm whales can't dive this deep for the first two to four years of their lives, so they're looked after by other members of the nearly all-female pod, while their mother dives in search of squid. 'This inability to dive deep when they're young is a great driver of the sperm whales' social system,' says Rendell.
The researchers also found that in this particular pod, the females made sounds much more often than the male calf. The adult females made 89 per cent of the codas of the 318 codas made in the 15 recordings.
'This suggests that adult females are much more vocal in social units than the younger whales are,' write the authors in their report.
Rendell is keen to find out how the mother's coda repertoire changes as her calf matures: 'Does she change back to her original repertoire?' he says.
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