Are Bird Feathers Waterproof?

Birds rely on their feathers for a host of important activities that help to ensure their survival:

They make it possible for birds to fly.
Their color is an indication of a bird’s health and stamina, which can influence the selection of a mate.
They serve as insulation from the cold.
They help to keep a bird dry.

Because feathers work to keep birds dry, many assume that they are naturally waterproof. After all, water does roll off a duck’s back. But it’s a little more complicated than that.

Feathers are able to keep a bird dry, not because of any inherent waterproofing, but because of their unique and highly complex structure and their arrangement with neighboring feathers. Birds maintain the integrity of their feathers’ structure and their alignment through preening.

What is Preening and How Does it Work?

There are many theories about the function of preening, but for our purpose, preening is a form of grooming. It is so vitally important to a bird’s overall health and well-being that all birds, even the ones that don’t fly, preen.

And they will do so several times a day.

One study examined the behavior of 62 bird species. The researchers discovered that, on average, these birds spent just over 9% of their time in maintenance behaviors, with nearly 93% of that time spent grooming.

When a bird preens, it is working to realign the barbules within its feathers. These microscopic barbules function a bit like Velcro—they interlock with tiny hooks—contributing to the feather’s structure and integrity. Multiply this realignment across 2,000 to 25,000 feathers (depending on the species) and you’ve got a nifty system for keeping water out.

As you can imagine, feathers take a beating with all that flying, exposure to the elements, and pesky, sometimes dangerous, parasites. So, in addition to aligning feathers, preening also helps to keep a bird’s feathers in tip top shape.

Preening Oil

Much like a conditioner helps to protect our hair and makes dragging a comb through a child’s wet and tangled locks less of a chore, preening oil conditions a bird’s feathers and makes it less difficult to align the barbules.

Like out hair and fingernails, feathers and claws are composed of keratin. And in the same way as our hair and fingernails are dead, so are bird feathers. But that doesn’t mean they don’t all need care.

Most birds have a gland at the base of their tail called the uropygial or preening gland. (I’ll stick with preening gland—at least I can pronounce that.) This gland produces a waxy oil, commonly referred to as preening oil, that birds use to coat their feather.

While preening, birds gather this oil with their beaks and carefully drag each feather through it. As they carefully align their feathers to maintain their optimal shape and position, ensuring their ability to fly, they evenly distributed this oil to remove dirt, dust, and parasites that would otherwise damage their feathers.

The oil also keeps their feathers flexible and waterproof.

Powder Down

You’ll recall that while all birds preen, not all birds have a preening gland. Generally speaking, birds without a preening gland are those that do not bath or submerge themselves in water. Birds without this gland include:

ostrich
kiwi
emu
cassowary
bustard
frogmouth
many pigeons
many woodpeckers
several types of macaws (hyacinth macaw, Lear’s macaw, and the Spix’s macaw)
parrots in the genus Amazona

Instead of a preening gland and preening oil, these birds have feathers—either found throughout or in distinct patches—whose barbules, when bitten, disintegrate into a waxy powder called powder down.

In the same way as some birds use preening oil, others use this powder to protect and waterproof their feathers.

The Exception

I found it curious to learn that barn owls have neither preen oil nor powder down.

While not true for all owls, barn owls have no waterproofing at all. Their feathers are specially designed for silent flight, which makes barn owls lethal hunters. But silent flight comes at a price—their feathers don’t keep the them dry.

A heavy rain or submersion in water and a barn owl’s feathers can become waterlogged. When that happens, they cannot fly; some actually drown. And an owl that cannot fly also can’t hunt. That can be bad news for the owl and the young owlets that depend upon their parents for food.