The strangeness of the animal world has no limit. On the other hand, its comprehension by us, bipedal animals, always depends on our curiosity, our stubbornness, our capacities of investigation.
More than a century after its first description, two American scientists have just provided a detailed explanation for an ornithological curiosity: the propensity of the namaqua sandgrouse to absorb water in its plumage, then to transport it to quench its young. . In the magazine Journal of the Royal Society Interface April 11two specialists in materials science describe, using microscopic images, the transformation of the bird’s feathers into real gourds and invite you to draw inspiration from them to design new systems for storing liquids.
It was in 1896 that the British ornithologist Edmund Meade-Waldo (1855-1934) first described the “curious habit” taken by the males of this southern African bird with the false air of a partridge, one of the fourteen species of the sandgrouse genus. Breeder of exotic birds in his vast property, he marvels at the tribulations of the namaqua sandgrouse, dipping his belly in a pond, squirming there to gorge his plumage with liquid before flying away towards the nest and his offspring. “But it seemed so incongruous that it took seventy years before the scientific community accepted it”says Jochen Mueller, assistant professor of civil engineering at Johns-Hopkins University (Maryland) and specialist in “intelligent materials”, the first signatory of the article.
Facing the aridity of the savannah
Two ornithologists from Cornell University (State of New York), Tom Cade and Gordon Maclean, published in 1967, in the magazine The Condor, the detailed description of the phenomenon. First of all, they note that the species always nests at a great distance from water points, up to thirty kilometres. An effective way to get away from many predators.
The strange behavior therefore allows him to face the aridity of the South African or Namibian savannah after the hatching of the eggs. By immersing his chest, the male absorbs a quantity of water corresponding to 15% of his weight (from 170 to 190 grams dry). Even if leaks and evaporation cause it to lose almost half of it during the return flight, the three chicks of the brood find something there to dip their beaks and quench their thirst.
But how does such a system work on a microscopic scale? Fascinated by the feathers, Mueller and his Massachusetts Institute of Technology (MIT) colleague Lorna Gibson set about studying those on the belly of the sandgrouse. By observing, using new imaging techniques, the three arborescent structures of the feather – rachis, barbs and barbules – they were able to detail the architecture of the last two. “The helical shape and the diameter of the barbules correspond to the ideal structure predicted by the theory”, marvels Jochen Mueller. Above all, they measured how the deformation of barbs and barbules under the action of water made it possible to keep the droplets intact despite the jolts of transport. “It’s like a wet spongecontinues the researcher. Only the outside lets the water flow out. But the sandgrouse’s plumage does much better, as it releases water as easily as it takes it up and stores it, without the need to squeeze it. And, once the operation is complete, the feathers are dry, while the sponge remains damp. »
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