This is birdnought.

As a duck swims slowly across a pond,

it skims the water with its broad bill slightly open.

This way of getting food is called dabbling.

Dabbling ducks feed near the surface,

without fully submerging like a diving duck.

Many ducks are expert dabblers,

including mallards, teal, and this gadwall.

Along with pond water,

multitudes of tiny particles pass through the dabbling duck's bill.

Somehow, it sorts out and swallows the tiny edible seeds and invertebrates,

while rejecting the tiny inedible bits of grit, mud, and debris.

The secret to how a duck pulls this off lies in its bill.

At the tip, and along the edges of the bill's inner surface,

there are many thousands of tiny sensory receptors,

some sensitive to touch, and others sensitive to movement.

In just one square millimeter of the duck's bill,

there may be several hundred of these receptors,

not to mention lots of taste buds.

So even though a duck doesn't see what is passing through its bill as it dabbles,

it can sense what it's taking in and carefully choose to eat or reject it.

So dabbling is much more than simply straining the water.

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