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| News :. Walruses prefer the right to the left
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Walruses have joined the fast-growing list of animals that, like humans, show a distinct preference for using one hand or limb - in this case, walruses are right-flippered - a new study suggests.
The discovery marks the first time an aquatic animal has been shown to have a flipper preference when foraging for food and is the first instance of handedness in the seal family, says a report today by a research team led by Dr Nette Levermann, of the Greenland Institute of Natural Resources and the University of Copenhagen, in the online journal BMC Ecology.
"It used to be thought that this trait was unique to humans, that right-handedness was linked to laterality in the brain due to the left hemisphere being used for speech and tool use," Professor Lesley Rogers, an expert on brain laterilisation at the University of New England, Australia, told ABC Science Online.
"This study and others show that this is clearly wrong. There are now many examples in animals - and not necessarily in our close [animal] relatives."
Examples have been found among fish, birds, reptiles, frogs and mammals, she said, suggesting strongly that the specialisation of one side of the brain for certain tasks occurred very early in the evolution of vertebrates (backboned animals).
Levermann's team notes that very little is known about the foraging habits of wild walruses, not least because of the dangers involved in getting close to these large and aggressive animals.
Caught on camera
But the team was able to use scuba divers to make 12 video-recordings of foraging adult male Atlantic walruses at depths of between six and 16 metres in Young Sound, off Northeast Greenland, in the summer of 2001. At least five different animals were involved.
Walruses are highly specialised feeders, eating bivalve shellfish that burrow up to 40 centimetres deep in sand and sediments on the sea floor.
Once they obtain a shellfish, the walruses suck out the soft fleshy contents, leaving the shell intact. Their feeding technique is clearly effective - the report notes that one walrus was found to have the remains of almost 6400 shellfish in its stomach.
The recordings revealed that the walruses use three different foraging behaviours to find the shellfish: swishing away sediment by beating a flipper; removing sediment by squirting a water-jet from the mouth; or rooting pig-like through sediment with the muzzle.
The animals anchored themselves with their large tusks, usually positioned to face the current, and with their bodies rolled at an angle of between 45 and 90 degrees to the sea bottom. The hind flippers were used only for moving forwards and backwards and the front flippers as stabilisers when the animals were not feeding.
But when they were actively seeking out shellfish using their favoured flipper-beating technique, the walruses used their right flipper - a trait known as dextrality - 89 per cent of the time. No walrus showed a left-flipper preference.
Because the sample size was small, the researchers also studied museum specimens and found evidence of a similar pattern of right-side preference in the shoulder and limb bones. "Measurements of the dimensions of forelimbs from 23 walrus skeletons revealed that the length of the right scapula, humerus, and ulna was significantly greater than that of the left, supporting our field observations of walruses showing a tendency of dextrality in flipper use," they say.
The scapula, or shoulder blade, in particular was much larger on the right side: "Many of the muscles that control the forelimb attach to this bone, which means that a longer right scapula could indicate a greater muscle mass associated with the right flipper.
"The implications of these findings suggest that tool-use and object manipulation is not mandatory for development of strong limb preferences approaching handedness."
Human skeletons show similar disparities according to the hand preference of the individual, they note. About 90 per cent of humans are right-handed.
Among other marine mammals, one study showed that 77 per cent of humpback whales used their right flipper to slap the water surface during behavioural displays.
Professor Rogers has discovered that chickens and toads show a clear lateral preference for certain behaviours: chicks seeking out fallen seeds preferentially turn their right eye to the ground, while at least three species of toads prefer their right forelimb for wiping debris from their faces.
Not all lateral preferences are to the right: when fish snap suddenly at food they tend to snap to the left, and a species of American lizard in the US tends to make courtship displays when another lizard approaches from its left. |
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