A whale’s varied vocabulary
EVER NOTICED HOW WELL sound travels underwater? Dr Rebecca Dunlop has. A researcher with the Humpback Whale Acoustic Research Collaboration (HARC), Rebecca spends up to eight hours a day analysing whale sounds. As a result, the HARC team has discovered that much of the sound humpbacks make is not part of the well-documented phenomenon known as “whale song”, but what is called “social sounds”.
Based at Peregian Beach, 110 km north of Brisbane, the HARC team has studied humpback sounds for four of the past seven years, during the whales’ southward migration in September and October.
“We aim to understand how whales are communicating and what the sounds mean,” Rebecca says. “We also want to understand the impact of both human-made and natural variations in ocean noise on humpback whale communication.”
Unlike humpback song, which is made up of the same drawn-out sound repeated over and over and produced exclusively by males, social sounds are short noises made by both males and females, Rebecca explains. “This is the first study of its kind in migrating humpback whales, and shows that they have a wide and varied communication system that is not limited to song,” she says.
SOCIAL SOUNDS ARE NOW emerging as another significant form of noise produced by humpbacks. “Social sounds primarily fall into two groups: vocal sounds, such as low grumbles or high chirps; and surface-generated sounds – for example, breaching and ‘pec-slaps’. We have identified 34 different vocal sounds – a surprisingly large catalogue compared to many other mammalian species,” Rebecca says.
Some vocal sounds, such as “grunts”, “groans” and “barks”, can be heard from whales that are joining into groups, while underwater “blows” or “cries” have been heard mainly in competitive groups – those with a number of males jostling for primary position with a female.
Low-frequency sounds, such as “grumbles”, “snorts”, and “thwops”, may be used more between members of the same group, while “wops” (one of the most common sounds heard – see glossary below) were recorded almost exclusively from mother-and-calf groups. These sounds may be used by a mother to keep in contact with her calf or may just be a call specific to females. Surface-generated sounds such as breaching or slapping are probably also used to communicate things such as size or position or simply to attract the attention of other whales in the area.
Studies elsewhere – in Hawaii, for instance – are focusing on the social sounds humpbacks make in breeding grounds and feeding areas. But the HARC team is looking closely at the whales’ social sounds during migration, as these may be different from feeding or breeding social sounds. “Migrating whales continually change group composition by splitting from, or joining with, other groups,” Rebecca says. “Mothers with calves are the only combinations that consistently stay together.”
MARINE MAMMALS RELY ON sound to communicate, but their success at “talking” can be severely affected by background noise – either human-made, such as ships, or natural, including wind, surf and other marine animals. “We’re also finding that humpback whales gradually switch from primarily vocal to primarily surface-generated communication when there’s a lot of background noise,” Rebecca says.
Just as humans use gestures as well as words to get their message across in a noisy environment, humpbacks may make surface sounds, such as breaching, as well as vocalising under water to help the receiver successfully understand the signal.
“Many animals modify the type of communication signal they use in different environmental conditions, including noisy settings,” Rebecca says. “But this is the first time we’ve seen a non-human species change from primarily using one type of communication signal [vocalisations] to using a secondary type of signal [surface-generated sounds].”
Source: Australian Geographic Issue 95 (Jul – Sep 2009)
Glossary: Vocal sounds
Wop: contact call between mother and calf
Thwop: contact call between whales and not limited to mothers and calves
Grunt trains: calls when pods are joining
Cry: male call when competing with other males to join a female
Underwater blows: male call when competing with other males to join a female
Surface-generated sounds
Breaching: communicates location and size when whales are splitting from a pod
Pec-slapping: call by females to solicit males when whales are splitting from a pod
LINKS
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