1. Domestic Ducks Were Tamed From Wild Mallards That Visited Lakes in Winter
Domestic ducks are believed to have been tamed from wild mallards, though there are exceptions like the Muscovy duck [1]. Mallards are birds widely distributed across the Northern Hemisphere. In Japan, they fly in to lakes and swamps as winter birds, but some individuals also raise young in northern Japan [2]. They feed on the water surface and often eat plant seeds like those of water plants [2]. In other words, a mallard needs a place with water and plant food on the surface. Those conditions can also be found in ponds and rice fields near people. The same guide says that white domestic ducks are genetically almost unchanged from mallards and can cross-breed with them [2]. So, when did people start keeping these birds close to their homes?
2. When People Began Keeping Ducks in Ponds and Rice Fields
Dictionary explanations state that there is a theory that China has the oldest history of domesticating ducks, and that they were also tamed in Europe around the turn of the era. However, there are not many archaeological materials to support this. It is also written that domestication is newer than chickens, and that there is no historical fact of domestication in ancient India, Greece, or Egypt [1]. In Japan, there are records of keeping ducks around the end of the Heian period. A farming book called "Nogyo Zensho," published in 1697 during the Edo period, also describes how to keep them [1]. However, a genomic study of domestic ducks published in 2021 (using 118 individuals) showed a picture slightly different from the common theory. It estimated that domestic ducks separated from mallards about 38,000 years ago, and from Chinese spot-billed ducks about 54,000 years ago. This is much older than the assumed time of domestication (about 1,000 to 2,500 years ago) [3]. This study reports that the ancestors of domestic ducks might be wild populations that are not yet known [3]. Note that this figure is not the time when people began keeping ducks, but the time when populations diverged, estimated from genetic differences. These are different quantities, so they do not necessarily conflict. Rather than overturning the common account, the story of the ancestors is becoming more complex as research progresses.
3. How Human Selection Changed the Duck's Body and Its Ability to Fly
Domestic ducks are said to have lost the ability to fly [1]. Wild mallards range widely, for example in seasonal migrations, but domestic ducks no longer need to. Instead, the traits that people choose show up in their bodies. A study published in Nature Communications in 2018 compared the genomes of 40 mallards, 36 ducks of 12 indigenous Chinese breeds, and 30 Pekin ducks. In Pekin ducks, human selection over several centuries continued. It suggested that a mutation in a gene called "MITF" may be involved in white feathers, and that the sustained expression of a gene called "IGF2BP1" may be involved in body size and feed efficiency [4]. Because the wording is "may be involved," the link between genes and traits is not established, and these genes do not seem to decide all of feather color or body size. The study does not address what caused white feathers to persist. Even with these changes in appearance, the stage for a duck's life remains waterside. Why do they not get cold even when floating in water for a long time?
4. How Preening Oil Keeps a Duck Warm in Cold Water
Ducks apply oil from an organ called the uropygial gland, located at the base of the tail, to their entire body of feathers using their beaks. This is called preening. Feathers coated with oil repel water, and it is introduced in duck observation guides that this makes the body less likely to get cold even on top of cold water [5]. There are also features in the feet that are submerged in cold water. The same guide explains that the feet have an organ for heat exchange, which makes it difficult for body heat to escape [5]. The reason they seem fine even when in cold water for a long time is partly due to the mechanism of their feet. If you see a duck preening, look closely to see if its beak is moving toward its tail. The body adapted to floating in water has also become a useful skill for humans. That is the work in rice paddies.
5. Aigamo: Hybrids of Mallards and Domestic Ducks That Work in Rice Paddies
Aigamo are hybrids created by crossing mallards and domestic ducks; they are birds made by people. They are released into rice paddies to eat weeds and pests, which is an organic farming method that reduces the use of pesticides. This method is called Aigamo farming [6]. Chicks are released after rice planting and retrieved when the rice ears begin to ripen, because they would eat the rice ears [6]. This method was established as a practical weeding technique by farmers in Toyama Prefecture around 1985 and became known nationwide through news reports. After the first Aigamo Weeding Discussion Meeting in March 1990, the method spread to other regions [6]. Because this account rests on a single reference entry, check the years and names against primary sources if you quote them. A rice paddy has water, and weeds and insects can be food, so it seems to be a good environment for a bird descended from mallards. That is our own reading, not a cause stated by the source.
Before You Go to See Ducks at the Pond
At home, you can try coloring paper with crayons and dropping a single drop of water on it. Observe how the water drop becomes round on the colored part. This can be a clue to imagine how duck feathers repel water with oil, but it is different from the mechanism of feathers themselves. At ponds or parks, if you see ducks or mallards pecking at their tails with their beaks, it might be preening. Observe from a distance without getting too close, and be careful of your footing near the water. Wash your hands after observing. To learn more, you can read the abstracts of the 2021 Zoological Research paper and the 2018 Nature Communications paper. Pay attention to the difference between "the time populations diverged" and "the time of domestication," and to how strong the wording "may be involved" is. This is good practice for judging how far a study’s conclusion can be pushed.