Direct observations of the underwater behaviour of free-living marine mammals are rare, especially if the animals are dangerous, like the walrus. This means that our understanding of these creatures is remarkably limited.
The scuba-diving researchers from Denmark, Greenland and Sweden went to Northeast Greenland to film male Atlantic walruses while they ate. Walruses eat invertebrate animals that live on the seabed. They are particularly fond of clams. Walruses suck out the soft part of the clam, and discard the empty shells. As clams can be buried up to 40 cm deep, the walruses must remove sediment to find them.
The videos showed that the walruses had four different types of foraging behaviour. They removed sediment by beating their right flipper, beating their left flipper, or using a water-jet from their mouth. They also rooted through the sediment using their muzzle – "like pigs in the ground."
The research team used the videos to assess how often the walruses used each foraging technique. They found that 66% of the time they used the right flipper, 4% of the time the left flipper, 29% of the time the muzzle and only 1% of the time the water-jet. When considering only flipper use, the walruses used their right flipper 89% of the time.
Right-handed people tend to have longer bones in their right arm than their left, probably because they use it more often. To see if the same was true for walruses, the researchers compared the lengths of the right and left scapula, humerus and ulna from 23 walrus skeletons. They found that walruses did indeed have longer bones in their right flipper.
Levermann et al. said: "The implications of these findings suggest that tool-use and object manipulation is not mandatory for the development of strong limb preferences or handedness."
BMC Ecology being an online journal is a most suitable media for making the kind of data files that have been analysed in the article available for the readers. Three movie clips of feeding walruses exemplifying the foraging techniques are attached as additional files in the article. Here we attach "Walrus using the flippers and muzzle for exposing bivalves."
This press release is based on the following article:
Feeding behaviour of free-ranging walruses with notes on apparent dextrality of flipper use
Nette Levermann, Anders Galatius, Göran Ehlme, Sřren Rysgaard, Erik W Born
BMC Ecology 2003 3:8
Published 23 October 2003
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