Duck: The waterbird that oils its feathers to stay dry

The duck is one of the most familiar waterbirds around us: it paddles calmly on the water, then shakes itself and its feathers are barely wet. How does it stay dry while swimming? Let's meet it.

Its body

The duck has a clever piece of "waterproof equipment": a gland at the base of its tail, called the preen gland, which produces oil. The duck spreads this oil through its feathers with its bill, as if applying a waterproof coating. So when it swims, the water does not soak in; back on land, a shake sends the droplets rolling off.

Its bill is flat — the "duck bill". Along its edges runs a comb-like structure called lamellae, which filters food from the water — so while feeding, a duck is often "sifting" out insects and seeds as it takes in water. Its feet are webbed, making excellent paddles.

Why it waddles

A duck's rolling waddle looks comical. It is not clumsiness: its legs sit far back on its body — a position that makes it a more powerful paddler, but leaves it less balanced on land, hence the side-to-side sway. In a sense, the duck has traded a little walking style for better swimming.

Where it lives and what it eats

Ducks are mostly omnivores, eating water plants, seeds, small fish, insects and aquatic invertebrates. Domestic ducks descend mainly from the mallard. They are social and often found on lakes, rivers and ponds.

A note for grown-ups

You could try a simple experiment with a child: smear a little cooking oil on paper, then drip water on it and see whether the droplets roll off. Using this to explain how a duck's oil keeps it dry is a lesson a child will not forget.