1. What Foods Do Pond Ducks Eat? Grass, Insects, and Shrimp
Picture a mallard dipping its bill into the water. Encyclopedia entries state that mallards eat leaves, roots, seeds, and grains [1]. Their diet also includes plant seeds, aquatic weeds, insects, and shrimp [1]. The spot-billed duck (karugamo) similarly eats seeds, roots, buds, and grains, along with insects and shrimp, as listed in field guides [2]. In autumn, they may also eat rice [1] [2].
So, the diet is mostly plants, but animals are included too. If ducks are resting on a pond during the day, when do they actually eat? This leads us to their daily schedule.
2. When Do Ducks Feed? Resting by Day and Eating at Night
You often see ducks floating peacefully in ponds during the day. However, encyclopedias note that mallards feed on grass seeds and grains in rice paddies and rivers, and this happens at night [1]. They rest in the pond by day and go out to eat by night.
Even for "pond ducks," the eating location is not always the pond. However, this description applies specifically to mallards; it does not state that every individual acts this way every night. It is safer to assume that feeding times and places vary by species and season [1]. So, how do they eat when they are actually in the water? To understand this, we must look at their bills.
3. How Does a Duck's Comb-Like Bill Edge Filter Water for Food?
A duck’s bill is flat. If you look at the edge, both the upper and lower parts have a shallow comb-like shape. A public relations pamphlet from the Chugoku Regional Development Bureau of the Ministry of Land, Infrastructure, Transport and Tourism explains that this structure filters out seeds floating on the water [5]. The duck takes in water along with food, then pushes the water out.
The shoveler (hashibirogamo) is known for this filtering method. It holds its bill horizontally in the water and opens and closes it narrowly to filter out grass seeds floating on the surface [6]. Surface-feeding ducks use these comb-like edges to eat items floating in the water. But how do they eat things below the surface?
4. How Do Ducks Feed Differently: Upside-Down Grazing and True Diving
Among surface-feeding ducks, there is a range of techniques. The gadwall (okayoshigamo) is known to stand on its head underwater to eat algae [7]. Field guides say freshwater ducks rarely dive, but in one specific wetland highlighted by the same pamphlet, both the northern pintail and the Eurasian wigeon dove frequently [7]. This was an observation from that particular site.
Other ducks make diving their job. The tufted duck (kinkurohaji) is a diving duck that eats shellfish often, as well as insects, shrimp, frogs, and aquatic plants [3]. A page from Tottori Prefecture notes they eat mollusks, crabs, shrimp, insects, and water grasses [4]. The same source mentions an observation where one dive lasted about 19 seconds, but this was just one example, not a standard length [4]. Distinguishing between "surface ducks" and "diving ducks" is only a rough guide. So, when do surface ducks really dive?
5. Why Do Mallards in Freezing Hokkaido Dive for Clams?
In the severe winter of Hokkaido, where water freezes, mallards usually feed at the surface. However, there is a record of them diving in brackish rivers (water mixed with seawater) to catch clams [8]. This was reported by Riko Oka in the Journal of the Japanese Ornithological Society, noting a water depth of about 1 m (about 3 ft) [8].
In this observation, the success rate for catching clams by diving was about 80%. The average dive lasted 6 seconds, with a maximum of 12 seconds [8]. The report also includes calculations for if a duck lived on clams alone. It estimates they would need to eat 1.1 to 3.5 times their body weight per day [8]. Since this exceeds their body weight, it should be read as an estimate for a hypothetical scenario where clams are the only food source.
The field guide idea that "plants are central" is correct as a broad rule. But mallards can change their feeding method depending on conditions.
6. Is Bread a Good Food? What Happens If You Throw It in the Pond
Seeing ducks in a pond, some people want to feed them bread. As we have seen, ducks are birds that skillfully find natural food and change how they eat.
Materials from Chiba City parks explain that large amounts of thrown food and bird droppings can worsen water quality [9]. They note a vicious cycle: if more waterfowl gather for food, feeding increases, which further pollutes the water. The materials also state that human food may contain ingredients undesirable for wild animals [9].
However, these materials do not say "bread always causes disease." The main focus is on water quality and the cycle of increased feeding. When observing, do not feed them; watch from a distance.
7. How to Spot Three Duck Feeding Styles on Your Next Pond Visit
If you see ducks in a park pond, try to categorize their feeding into three types: moving their mouths at the surface, standing upside down, or diving [8]. Watch for about 10 minutes and write the numbers in a notebook. If there are no ducks, note that too.
Do not get too close to the pond edge; watch from a distance with an adult present. Do not feed them [9].
If you change the season or location, the numbers might change. If you see a surface-feeding duck diving in a winter pond, it could be an example of changing methods based on conditions, like the report mentioned earlier. Write down when, how many, and which species to review later.
To learn more, Riko Oka’s report is available in Japanese on J-STAGE [8].