16 | NewScientist | 25 June 2011

IN MOTION-CAPTURE technology, actors are tagged with markers and videoed, allowing their movements to be transferred to lifelike digital creatures such as Gollum in The Lord of the Rings. Individual strands of DNA or proteins could get tagged up too, and their complex motion tracked in three dimensions.

This may be possible thanks to a device designed by Na Liu at the

University of California, Berkeley, and colleagues. It is made up of five gold bars, each a few hundred nanometres long and arranged in the shape of a 3D letter H: four of the bars sit parallel to one another to form a rectangular cage, while the fifth lies crossways inside it.

In each bar, electrons vibrate at a natural frequency. Put the bars in this arrangement and these vibrations, known as plasmons,

Drought killed bird, not early humans

TIME for a retrial? It seems that humans were not responsible for the extinction of a large flightless bird within 10,000 years of setting foot in Australia, as was suggested in 2005. We had an alibi: the bird was already on the way out when humans turned up 55,000 years ago.

Around 45,000 years ago 90 per cent of Australia’s large animal genera disappeared, including the bird Genyornis newtoni. An analysis of carbon isotopes in fragments of fossilised eggs showed sudden dietary shifts followed by extinction.

Using a different statistical approach, Brett Murphy at the University of Tasmania, Australia, says there is “good evidence” that the decline happened gradually due to changes in rainfall, beginning 80,000 years ago – long before humans arrived (Global Ecology and Biogeography, DOI: 10.1111/j.1466-8238.2011.00668.x).

Parrots join apes and Aristotle in the club of reason

HUMANS do it. Great apes do it. Now a parrot has shown it can use logical reasoning to work out where food is hidden.

Sandra Mikolasch of the University of Vienna’s Konrad Lorenz Research Station in Austria and her colleagues first checked that seven African grey parrots (Psittacus erithacus) had no preference for the two types of food on offer, seeds or walnuts. Then each parrot watched a researcher hide a walnut under one opaque cup and a seed under another. Next the researcher hid the cups behind a screen, removed one of the treats and showed the bird which one had been taken. Finally, the screen

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Tagging molecules, Hollywood-style combine to form two sharp resonances that vary depending on the position of the central bar relative to the cage (Science, DOI: 10.1126/science.1199958).

Liu’s team suggests attaching each bar to a different point on a 3D molecule. As the molecule interacts with an enzyme, or folds up, the distances between the rods will change, producing a series of plasmon resonances that can be measured to reveal the molecule’s motion in three dimensions.

was removed to see if the parrot could work out which treat must remain, and under which cup it must be.

Only one of the parrots, a female called Awisa, was able to do this, choosing correctly in three-quarters of the tests – 23 out of 30 (Biology Letters, DOI: 10.1098/rsbl.2011.0500). “So far, only great apes have been shown to master this task,” says Mikolasch. As with the parrots, only some apes could solve the problem, she says. “So we now know that a grey parrot is able to logically exclude one possibility in favour of another to get a reward, known as ‘inference by exclusion’.”

The other parrots chose more randomly, suggesting they hadn’t worked out what was going on. But they did show their mettle in easier tests, where the cups were in view throughout.

WHAT doesn’t kill you makes you denser – at least for the innermost planet. It seems Mercury lost its rocky outer layers in a youthful brawl with another world. That could explain why its dense metal core makes up a whopping two-thirds of its total mass.

Observations of the composition of Mercury’s surface by NASA’s Messenger probe, which has been orbiting the planet since March, seem to have ruled out other explanations for its high density. One such theory had it that the sun vaporised much of Mercury’s surface early on. That should have left few volatiles, such as potassium, on its surface, but Messenger found no such depletion, mission scientists reported on 16 June.

Early bash trimmed Mercury’s puppy fat