Swans are the gentle giants of my local waterways: floating paragons of snowy serenity that cruise peacefully through muddy brown water amid the rowdy confusion of their smaller brethren.
And they present a puzzle. Around them, mallards, Egyptian geese and Mandarin ducks have plumage so varied that it seems like any little speck of dirt or grime would disappear into the design. But the swans, paddling around in water so opaque that their feet can’t be seen, tip their tail feathers high in the air to forage underwater for the deepest plants—yet they re-emerge an unreasonably pure white. How do they stay so clean?
[…]
Just as a swan uses an oily coating to repel water, to get rid of oil it needs a watery coating. And the answer—discovered only three years ago in a paper published in the journal Advanced Functional Materials—is saliva. A swan’s spit is full of proteins that have a water-loving end and an oil-loving end. Once in a while, the bird distributes saliva on its feathers instead of preen oil, and the oil-loving ends stick to the feathers, leaving the water-loving ends exposed.
This makes the feathers attractive to water, and so allows the watery saliva to penetrate deep into the feathers. Once it’s there, it finds channels lined with tiny wedges. The wedge shapes help surface tension push the water from the center of the feather to the edges, sweeping along and clearing out any tiny droplets of oil or fat on the way.
The feathers get a watery deep cleaning as the tiniest oily contaminants are carried away. After a while, air dries the saliva out, and the surface returns to its normal water-hating state while the swan is restored to its pristine purity.
It’s a fascinating system, and scientists and engineers are now trying to replicate it to make self-cleaning fabrics that we could use. But kudos to the swan, for having evolved the perfect spit-and-sparkle system for keeping itself clean.
Read full article here.
— Helen Czerski, from “How Swans Stay White in Muddy Waters” (Wall Street Journal, June 6, 2024)
DK Photo: May 31, 2023. 4:30 am. Cove Island Park, Stamford, CT. More photos of the swans from that morning here.
