Science  02 Nov 2012:
Vol. 338, Issue 6107, pp. 588

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  1. Sand Grains Make Dunes Sing


    When whipped by desert winds, sand dunes signal their displeasure with haunting moans that reverberate across the arid landscape. Some emit single notes while others mimic a jumbled chorus, but what causes different dunes to sing different songs has been a mystery—until now. Scientists at Université Paris Diderot collected sand from a singing dune in Morocco that moans at around 105 hertz (Hz)—or, to a musician, G-sharp two octaves below middle C. They compared those grains to sand collected from a dune in Oman, which produces notes ranging from 90 Hz to 150 Hz (F-sharp to D). As they reported in a paper published online last week in Geophysical Research Letters, the scientists reproduced these desert songs by sliding sand down inclines in the lab, indicating that the synchronized movement of sand grains produces the famed moaning. When they sieved the Omani sand so the grains were similarly sized, the resulting “avalanche” produced a single-note song. Grain size, they conclude, determines the notes contained in a dune's song.

  2. Cool as a Ball of Dung


    If you've ever run barefoot across a sizzling beach in summertime, imagine what the dung beetle endures as it works the African savanna, where midday surface temperatures can exceed 60°C. The beetles, however, have an ingenious trick for keeping cool, according to a study published on 23 October in Current Biology. They take periodic breaks from rolling their balls of dung and climb atop their cargo, which stays up to 30° cooler than the ground because of evaporating moisture.

    The researchers, from Sweden and South Africa, noticed that the beetles clambered onto their dung balls more frequently as the surface temperature rose. Using infrared thermography, they found that the temperature of the beetles' front legs decreased up to 10°C during these interludes. When they dipped the beetles' front legs in silicone to form tiny insulating boots, the beetles could better tolerate the hot sand and climbed on the dung balls less often. A dung ball provides a “mobile thermal refuge,” the researchers conclude, by providing elevation above the ground and absorbing heat directly from a beetle's legs when it climbs atop, and by cooling the the sand in front of the beetle as it pushes the ball along.