1. The Ancestor of the Domestic Duck: The Wild Mallard
The domestic duck is said to have originated from the wild mallard, which was tamed by humans [1]. The timing of this domestication varies by source, with some suggesting around 1500 BCE in East Asia, while others say about 3000 years ago [1][2]. In Japan, domestic ducks are thought to have arrived around the 12th century [2].
So, what does the original mallard eat? Dictionaries state that outside of the breeding season, their diet is mainly plant-based. They eat grass leaves, roots, fruits, grains, and seeds of aquatic plants, but they also consume insects and shrimp [3]. Another description notes that they take grass seeds and grains from rice paddies and rivers at night [3].
Even within the duck family, eating habits differ. Ducks that feed at the water’s surface, like the mallard, often eat plant matter such as aquatic plant seeds. Ducks that dive underwater are said to eat more animal matter, such as shellfish [4]. When you see a duck searching near the surface in a park, it may be connected to these natural feeding methods of the wild mallard.
2. The "Teeth" on the Beak: Filtering, Not Chewing
If you look at a duck’s beak from the side, you will see fine comb-like plates called lamellae along the edge. Although they look like teeth, they are not used for chewing [5]. Instead, these plates act like a net, filtering food from water and mud. The duck takes in water and mud, then pushes it out, keeping the edible parts inside. This is similar to lifting boiled noodles out of hot water with a strainer, where only the water falls away.
However, unlike a hard kitchen strainer, the edges of a duck’s beak are soft and sensitive. It is said that many ducks use touch as a clue to find food, not just sight [5]. They swim, dip their bills, touch the bottom, and filter the water. The movement of a duck’s bill in a pond is likely supported by this unique structure.
3. Upside-Down and Digging: How Mallards Get Lotus Roots
A study published in the Journal of the Japanese Ornithological Society observed mallards eating lotus roots in Ibaraki Prefecture [6]. For roots near the water’s surface, the ducks took an upside-down posture, putting their necks into the water to grab them. For roots deeper down, they reportedly used their feet to stir up the mud and dig them out [6].
This behavior shows that ducks use their long necks and moving feet to probe through mud, which is different from the image of a bird simply floating on water. It is important to note that this was an observation of wild mallards, not domestic ducks. It serves as one example of how the original species feeds.
4. What Domestic Ducks Eat: Feed and Vegetables
Dictionaries describe domestic ducks as omnivorous and big eaters, said to consume twice as much as chickens [1]. If allowed to roam freely, they can be raised on roughage like grass alone. However, they are usually given a mixed feed made for chickens, combined with green grass, vegetables, and leftover food [1]. This approach connects to the wild mallard’s habit of eating grass and seeds.
Ducklings have different needs. A veterinary manual states that duckling feed requires higher protein levels and more niacin, a type of vitamin B3 [7]. For Peking ducks, the requirement is about 55 mg per kg of feed, which is roughly double the 27 mg needed by young chickens [7]. Research also suggests that feed with about 20% protein is suitable for the first three weeks of a duckling’s life [8]. This shows that feed requirements differ between species and change as the bird grows.
5. Is Bread Good for Park Ducks? Opinions Differ
Feeding bread to waterfowl is not recommended by animal protection groups, according to articles introducing their views [9]. The reasons cited include: first, bread has little nutritional value; second, it may weaken the duck’s instinct to find its own food and reduce their wariness of humans; and third, leftovers can accumulate in the water, leading to algae growth and poor water quality [9]. Alternatives suggested include bird feed, grains, and vegetables.
However, these are opinions from overseas organizations introduced in a Japanese article, not official rules from Japanese government offices [9]. The same article notes that some views consider bread a valuable energy source for swans in winter. Because opinions are divided, it may be more helpful to understand "why" some say bread is bad, rather than deciding it is strictly forbidden.
6. Aigamo Ducks: Working in the Rice Paddy
Aigamo is a common name for a crossbreed of mallard and domestic duck. It does not exist in the wild and is described as a domestic bird bred for food [2]. Releasing these birds into rice fields to eat weeds and pests is known as Aigamo farming [10]. The birds’ droppings are also said to act as fertilizer [10].
Eating both weeds and insects is a job that works because the ducks are omnivorous. This connects to the mallard’s natural diet of grass, seeds, and insects mentioned earlier. However, when the rice ears begin to ripen, the ducks are removed from the field so they do not eat the rice [10]. Humans decide what the ducks can and cannot eat, defining their work in the field.
7. Observing Feeding Behavior at the Water’s Edge
You can observe how ducks and mallards search for food from a distance at a pond or river. Do not get too close to the water’s edge or reach out your hands. Look for specific behaviors: Is the duck dipping its bill in the water? Is it upside down with its neck submerged? Is it stirring mud with its feet? Write down what you see and compare it with the descriptions in this article.
At home, you can try an experiment. Put cabbage pieces and corn kernels in a bowl of water. Gently scoop them up with a tea strainer. The water drains away, leaving only the larger items. Imagine that the plates on a duck’s beak work like this tea strainer.
To learn more, the Ministry of Agriculture, Forestry and Fisheries public relations magazine (aff) from December 2016 features a special report on agriculture that includes Aigamo ducks. You can find the details in the source list under [2].