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Domestic ducks called crested ducks descend from the mallard and feature a mutated gene that causes feathers to sprout from the top of their heads. The crest represents a deformity in the skull where a lump of fat protrudes through an opening in the bone. Feathers sprout from this tissue in varying amounts, which might range from a few wisps to a full crest that resembles a powder puff. Two main types of crested duck are the black and the white varieties, but cross-breeding produces gray and other colors.
Breeding a crested duck might be difficult because the gene responsible for the deformity causes about one-fourth of eggs to die before hatching if both parents carry the gene. Another 25 percent of ducklings might die after hatching because their brains are exposed. If only one parent carries the mutated gene, half of the ducklings that survive will be crested. Eggs hatch in 28 days.
The crested duck originated in Great Britain and has existed for thousands of years. It can be bred with any other domestic duck, except the Muscovy. In some parts of the world, these waterfowl are bred for exhibition, with large, symmetrical crests considered more desirable. Some people raise these fast-growing ducks for eggs or meat, while others keep them as pets.
The practice of breeding the crested duck for show might be banned in some regions because studies show coordination problems in this species. One study showed the size and location of fatty lumps creates smaller brains and olfactory openings in offspring. The number of feathers in the crest has no bearing on coordination limitations.
Some crested ducks cannot get up if they fall onto their backs. They might tumble down when walking or walk with a distinct gait indicative of coordination problems. One research study developed a test to identify birds with these defects so breeders can begin eliminating them through selective breeding. People buying crested ducks might use the test to identify healthy stock for the best breeding.
Scientists found some crested ducks needed more than a minute to flip onto their feet after being placed on their backs. These ducks had more fatty tissue in their craniums. Birds intended for breeding should right themselves within one or two seconds, researchers concluded.