Like water off a duck’s back

It’s obvious where that expression, “like water off a duck’s back” came from.  Duck feathers shed water amazingly well — their plumage seems almost impenetrable.

Droplets of water bead up and slough (or sluff) off the outer feathers of duck plumage.  This guy had just righted himself from tipping up to scrounge algae off the rocks at the bottom of the creek bed.

No doubt part of staying warm in the chill winter temperatures and winds is staying dry, and duck plumage is intended to do just that.  Not only are the feathers incredibly dense, laid down in overlapping layers in feather tracts, but they are coated with a waxy residue from a gland at the base of the ducks tail that waterproofs them.

Beads of water are shed from all surfaces from head to tail end on this hen Mallard.

But what about those bare feet, exposed to near freezing water temperatures and standing on cold rocks or ice or snow for hours on end?  Feet don’t shed water, just the feathers.

Cold toes?

This drake has just climbed out of the water, and is standing on ice, not something we would be comfortable doing (barefoot).  What happens when we reach for ice cubes in the freezer with wet fingers? The ice sticks to our fingers and is difficult to remove without losing some skin in the process. So how do ducks keep their wet feet from sticking to the ice?

Ducks slip and slide on ice, but their feet don’t stick to the surface.

The secret is to maintain very cold toes that are the same temperature as the surface on which the duck stands or walks.  This is achieved by having arterial blood going to the foot run in parallel with the vein that is bringing cold blood back from the foot — making a heat exchange unit that promotes cooling the extremities while preserving the warmth of the body core.  Engineers have used this principle in the design of heaters and air conditioners, among many other uses.

And this makes it nice for ducks to stand around admiring their reflections in icy pools.