I took this photo of a great egret last month - I have never seen one shake so earnestly, though I'm guessing it happens all the time. I was watching this one for about 30 minutes - there were occasional gusts of wind messing up its feathers. I guess he had about enough of that, as he stood and shook back and forth like a wet dog. Afterward, I though I was looking at an overgrown chick! :)
Plumage integrity is crucial to birds and they spend a lot of energy in maintenance. Even a slight disturbance of the micro-structure of the outer, or contour feathers, can allow water to penetrate and start to soak the down feathers underneath- much the same as if you had a cut in the outer shell of your down jacket. I would guess that a big shake like this rearranges the macro-structure of the plumage to put everything generally in the right place. This is often followed by preening where the bird works on individual problem areas to zip-up the feather micro-structure- the barbs, barbules and hooks, and maybe spread a bit of preen oil and wax if they have a preen gland. The micro-structure produces a covering with only very small holes in it, so that water cannot penetrate due to its surface tension- like the canvas of a tent. The oils and waxes from the preen gland provide a feather conditioner, making the feathers more slippery and thus allowing them to come back into place easily if disturbed. Their contribution to actual waterproofing is minimal.
We tend to take feathers for granted but they are an absolutely remarkable product of evolution if you think about their properties, structure and function.
Yes - thank you John. That is very interesting. In fact, directly after this photo was taken, the egret started to preen for quite some time.
The more I learn about identification and behavior, the more interesting it becomes to just sit and watch. Nature continues to be miraculous and fascinating!
Shaking like a wet dog
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