Most birds that live on water are engineered to stay dry. A mallard's plumage sheds rain like a good jacket, and the air trapped beneath it keeps the bird riding high on the surface. The cormorant took the opposite approach. Its feathers soak through, its body sits low in the water, and it sinks with a few kicks of its feet. What looks like a design flaw is better understood as a trade: the cormorant surrendered some comfort and warmth in exchange for one of the most effective underwater hunting kits in the bird world.
Air is the enemy of a diver. A duck dabbling at the surface carries a thick layer of air in its plumage, and that layer contributes heavily to its buoyancy. For a bird that only upends to graze on plants, this is fine. For a bird that must chase fast, slippery fish through open water, it is a tax paid on every dive. Each time the bird goes under, it must push against a force that wants to shove it back to the surface, and every extra push burns energy.
Different lineages have solved this in different ways. Penguins and auks compress their plumage and rely on powerful wings. Loons have dense bones and legs set far back on the body. Cormorants share several of those tricks, but they added one that is rare among fish-eating birds: they let the water in.
Waterproofing in birds is less about oil than most people assume. The preen gland, which produces a waxy secretion, plays a role, but the main barrier against water is structural: the spacing of the barbs and barbules that make up a feather's vane, and the surface tension that forms across those tiny gaps. Where the spacing is fine and the feather is stiff, water beads up and rolls off.
Cormorant feathers appear to break that rule on their outer surface. Research beginning in the 1960s, and later studies of great cormorants, found that the outer plumage is built so water can penetrate it, while a finer layer close to the skin holds a thin film of air. The result is partial wettability rather than total soaking. The bird is not a sponge; it is a diver wearing a thin air-trapping undersuit beneath a leaky shell. Shrinking that air layer cuts buoyancy, so the bird spends less energy fighting its way down.
Feathers are only part of the package. Cormorants have fully webbed feet, with all four toes joined by skin, and legs set well back on the body. That makes them powerful paddlers underwater and clumsy walkers on land. The long bill, hooked at the tip, is shaped for gripping slippery prey, and many species swallow fish whole after surfacing. Their eyes can focus both in air and underwater, a useful skill for a bird that switches environments constantly, and their skeletons appear to be relatively dense compared with those of surface-feeding waterbirds.
Together these traits make the cormorant a pursuit diver in the strict sense. It does not plunge from the sky like a gannet or wait in ambush like a heron. It swims down and runs fish to ground in their own element. People have exploited exactly that skill for centuries: fishermen in China and Japan trained tame birds to catch fish for them, a tradition documented under cormorant fishing.
Nothing here is free. Water conducts heat away from the body far faster than air does, and a soaked bird loses warmth quickly. Studies of great cormorants have shown that diving can be thermally expensive, and that the savings from reduced buoyancy have to be weighed against the cost of keeping the body warm. Cormorants appear to manage the bill by eating a great deal, by making short, frequent dives, and by choosing habitats where the trade makes sense. Even so, the family lives from the tropics to sub-Antarctic coasts, which shows the bargain can pay off in a wide range of climates.
The familiar pose, perched on a piling with wings held wide, is the visible side of that bargain. A bird with wettable plumage must dry out and rewarm between fishing bouts, and spreading the wings exposes the feathers to sun and wind. The exact function is still debated, and some researchers have suggested the posture may also assist digestion or balance. Whatever the full story, it is common across the family and fits neatly with a wettable-plumage lifestyle, as described in the Cornell Lab of Ornithology's guide to the double-crested cormorant.
Cormorants belong to the order Suliformes, alongside gannets, boobies, darters and frigatebirds. Each group found its own way to make a living from fish. Gannets and boobies strike the water from the air, cushioned by air sacs beneath the skin. Frigatebirds avoid the water almost entirely, snatching food from the surface or stealing it from other birds. Darters, the cormorants' close relatives, spear fish with their sharp bills and also have wettable feathers, which suggests the trait may be older than the cormorants themselves.
The exact sequence is not settled. Wettable plumage may have been inherited from a shared ancestor or may have evolved more than once, and fossil evidence for soft features such as feather microstructure is thin. What the pattern does suggest is that low-buoyancy, fish-chasing bodies were a path this lineage was already walking, and that cormorants simply followed it furthest.
The Galápagos offer the most dramatic example. The flightless cormorant, found only on the western islands of Fernandina and Isabela, has tiny wings, a reduced keel on its breastbone, and a heavier body than its flying relatives. With plentiful food in cold, nutrient-rich waters and few land predators, flight became a cost with little benefit, and the bird became a pure diving specialist. It is the logical endpoint of the cormorant strategy.
The cormorant's leaky plumage is easy to mistake for a missing feature, as if evolution forgot a step. It is more accurate to see it as a bet that paid off. In waters rich in fish, a bird that can dive cheaply and stay down long enough to catch prey can feed its chicks, hold its territory and breed successfully, even if it spends the afternoon on a rock drying out. Natural selection does not reward comfort. It rewards the compromise that leaves the most offspring.
That logic holds for every adaptation in the group, from the webbed feet to the dense skeleton. There is no perfect waterbird, only different answers to the same problem of living between air and water. For a deeper overview of the family, see the Encyclopaedia Britannica entry on cormorants. The cormorant's own answer is to let the water in and make peace with the cold.