Ducks are adapted for swimming in water. They are adapted to catch food in water and to take flight from water. But ducks' behavioral adaptations, to water or otherwise, are often related to their physiological adaptations. Scientists tend to focus on those morphological changes, but when behavioral traits link with genetic traits, the behavioral adaptations take root in the species through the power of selection.
The webbed feet of a duck are designed for swimming. They extend and contract in different ways to maximize the duck's movement in the water. The feet are quite tough and contain no nerves or blood vessels, allowing the duck to swim in icy waters. The webbing tends to cause the waddling characteristic of ducks. Different species have variations of the same adaptations; mandarin ducks, for example, have stronger gripping power in their feet because they seek shelter in trees when not in the water.
The beak, or bill, of the duck, the duck's diet and the way it captures food are interrelated. All ducks have lamellae, or bony protrusions, on their beaks, but some have wider bills with membranes allowing the filtering of water for smaller animals. Others have longer, serrated bills for carving fish, mollusks, and amphibians. Ducks also use their beaks to spread oil onto their feathers.
A duck behavior, called preening, allows a duck's feathers to be water resistant. The preen gland, located near the base of the tail, secretes an oil that ducks then rub with their beaks and heads onto their feathers and all over their bodies. The oil on a duck's feathers keeps the bird dry. Staying dry means staying warm and light for swimming and flying faster.
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The mallard is an example of both physiological and behavioral adaptations. The females have brownish feather camouflage that mimics the reed-covered water. The young have a similar coloration before maturation. While the males have the distinct green head, they will lose much of their coloration after breeding. Females are left to raise the young, so if danger approaches, the female will quack loudly and fly away to draw the predator to herself. The babies have been taught to remain still and silent. If the predator continues its pursuit, the female will fly on to open water and pretend to be injured. The mallard is able to take flight from the water almost vertically because of the combination of the force of its wings and the paddling of its feet.