The bird that I’m referring to in the title is the Namaqua sandgrouse. It’s remarkable animal. It weighs 180 grams and yet is able to carry 25 grams of water as far as 20 miles to its nest in its feathers.
It is a bird which is been thoroughly adapted to desert life in south-western Africa by being a sponge to pick up water in its feathers. It dunks itself into water and its absorbent feathers store the water against their breast. They can then fly back to the nest and their young drink the water from their feathers.
The Namaqua sandgrouse was observed in 1896 by Edmund Meade-Waldo, an English ornithologist. He saw the Namaqua sandgrouse exhibit ‘strange behaviour’. He wrote:
He would rub his breast violently up and down on the ground and when all awry, he would get into his drinking water and saturate the feathers of the upper parts. The young will run out, get under him and suck the water from his breast.
What he is saying there is that the Namaqua sandgrouse would first rub their feathers on dry ground to ruffle them up to make them more absorbent and then walk into water. The feathers in this state were optimal to utilise capillary action (see below).
He realised that the bird had adapted to desert life in using the feathers as a sponge. How can these feathers be so absorbent?
The news in the press today is that the scientists have investigated sandgrouse belly feathers properly for the first time.
Jochen Mueller of Johns Hopkins University found that 1 gram of sandgrouse feathers could store 8 grams of water. They observed the feathers with electron microscopes in their dry and wet states.
They discovered that the feathers consist of a shaft connected to barbs which are also connected to barbules. The barbules formed tubular structures of exactly the right size to exploit a phenomenon called capillary action.
Capillary action is the movement of water within spaces of a porous material due to the forces of adhesion, cohesion and surface tension! That comes from the United States Geographical Survey.
Nearer to home, a good example of capillary action can be seen when you dip the corner of a sheet of kitchen paper – the absorbent paper you can buy in supermarkets – into a bowl of water. The water quite rapidly rises through the paper through capillary action. Another good example is sap arising from roots in trees.
And once the water has been absorbed into the feathers through capillary action, it can then be sucked out by the chicks.
Through evolution, the feathers have been precisely engineered to suck up water only. An amazing example of eons of evolution allowing a bird to adapt to very dry conditions and to provide water to her young successfully.
