What Keeps Ducks Afloat?

On January 29, 1992, a cargo ship accidentally released thousands of small yellow rubber ducks into the Pacific Ocean. Remarkably, many of these ducks are still drifting today, enduring the journey across the globe. They've traveled along the U.S. eastern coastline, near Greenland, and even through Arctic ice packs [source: Bruxelles].

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The ability of these common bath toys to stay afloat for over 15 years isn't surprising. Made of rubber and filled with air, they are incredibly lightweight, allowing seawater to support them easily. But how do real ducks, made of flesh and blood, achieve the same feat? Unlike rubber ducks, they aren't hollow and contain more than just air.

The idea is straightforward, but grasping it requires an understanding of why objects float. Whether something floats or sinks in water depends on a principle known as buoyancy. If an object weighs less than the water it displaces, it floats; if it weighs more, it sinks.

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Had the cargo ship been carrying bowling balls, they certainly wouldn't be drifting across the ocean. Rubber ducks, on the other hand, weigh around 5 grams and occupy about 75 cubic centimeters of space. The water they displace weighs roughly 75 grams (0.16 pounds), far exceeding their own weight. Naturally, the denser seawater keeps them buoyant.

Real ducks are also lighter than the water they displace, but achieving this buoyancy involves multiple factors working together. Discover why it's more complex than just rubber and air in the next section.

Floating Feathers, Uropygial Glands and Hollow Bones

Despite not being particularly heavy, ducks rely on specific traits to stay afloat. Without these, they would likely sink to the bottom of lakes instead of gliding on the surface.

A crucial feature aiding ducks in staying buoyant is the uropygial gland, also known as the preen gland. Situated near the tail, this gland secretes an oil that ducks spread over their feathers to make them water-resistant. By repelling water, their feathers prevent saturation, keeping the birds lighter. Some experts believe that without this waterproofing mechanism, ducks might struggle to stay afloat and could even drown.

Beyond their waterproof feathers, ducks benefit from another floating aid: air-trapping feathers. Their plumage is designed with interlocking barbs that capture air, much like the inflatable armbands children use in the pool. When ducks need to dive, they compress their feathers to release the air, and upon resurfacing, they shake to trap air again.

Ducks also possess internal air sacs that enhance their buoyancy. These sacs, connected to their lungs and distributed along their body, remain filled with air unless the ducks choose to dive. By expelling air, they can submerge, and these sacs act like tiny built-in flotation devices.

Ducks, along with numerous other bird species, have hollow bones. These bones, known for their strength and lightweight structure, enable birds like cardinals and hawks to take flight effortlessly. Similarly, this lightweight design aids ducks in both floating and flying.

Interestingly, many bird species share traits that contribute to buoyancy, such as waterproofing glands and hollow bones, suggesting they should also float. Research on the impact of oil spills on bird mortality reveals that around 90 percent of birds remain afloat for at least two weeks if they perish in the ocean [source: Tomasi].