Swans are among the largest waterfowl species, commonly found inhabiting freshwater wetlands, lakes, rivers, and coastal inlets across temperate regions. These large birds require a substantial amount of food, which they acquire through foraging both on water and on land. Their diet is primarily plant-based, making them largely herbivorous, though they are opportunistic feeders who supplement their intake with small organisms found within their watery habitats.
Primary Aquatic and Terrestrial Vegetation
The majority of a wild swan’s diet consists of aquatic plants, which they access using their long, flexible necks. Swans commonly employ a feeding technique known as “up-ending,” where they tip their bodies forward to reach submerged plants anchored to the bottom. This technique allows them to graze on vegetation inaccessible to many other waterfowl.
Their preferred submerged plants include pondweed, waterweed, and muskgrass. Swans consume the leaves and stems, but also seek out roots, tubers, and rhizomes less frequently. They regularly consume floating vegetation, such as duckweed and algae.
When aquatic resources are less abundant, swans move onto land to graze on terrestrial plants near the water’s edge. They eat fresh grass, clover, and the leaves of wild marsh plants. This land-based foraging is important in colder months or in agricultural areas where they may consume grains, wheat, or leftover root vegetables like potatoes.
Small Prey and Invertebrates
While plant matter forms the bulk of their intake, swans incorporate animal protein into their diet, often incidentally, as a secondary source of concentrated nutrients. They consume small aquatic invertebrates, which often cling to the submerged plants they pull up.
These protein sources include:
- Snails
- Small crustaceans
- Insect larvae
- Mollusks
Adult swans may occasionally eat small amphibians, such as tadpoles, or small fish, but this is less common. The intake of these small organisms is particularly important for cygnets, who require higher levels of protein for rapid development.
Seasonal Changes and Energy Demands
A swan’s diet is flexible, shifting throughout the year in response to seasonal food availability and physiological needs. During spring and summer, vegetation is abundant, and swans focus on consuming tender, new growth to support nesting. Diatoms and soft aquatic plants are consumed heavily during breeding periods to accumulate necessary protein and energy.
As autumn progresses, swans transition to more energy-dense foods, such as grains and tubers, to build fat stores for migration or winter survival. When water sources freeze or vegetation dies back, they increase their reliance on terrestrial grazing, seeking out grasses, seeds, and leftover crops. Increased caloric needs during periods like nesting, molting, and migration require the swan to actively adjust its foraging strategy.
Harmful Human Foods and Why They Should Be Avoided
The practice of feeding wild swans human food, while often well-intentioned, is detrimental to their health and natural behavior. Foods like bread, crackers, chips, and other processed items should never be given to waterfowl. These items are often described as “empty fillers” because they lack the necessary vitamins, minerals, and protein a swan requires for proper nutrition. A diet dominated by such low-nutrient, high-carbohydrate foods can lead to severe malnutrition, even if the bird feels full.
A related concern, particularly for young cygnets, is “angel wing,” a condition where nutritional deficiency causes the wing joint to develop improperly. This leads to a permanent outward twisting of the flight feathers, rendering the bird unable to fly and limiting its ability to forage naturally or evade predators.
Uneaten human food tossed into the water can quickly turn moldy, causing severe intestinal problems. The rotting food also contributes to water pollution, encouraging harmful algae and attracting pests. Furthermore, feeding swans causes them to become habituated to humans, making them less likely to forage naturally and potentially leading to aggressive behavior.