The Trumpeter Swan (Cygnus buccinator) is North America’s largest native waterfowl. Its massive size requires an abundant and specialized diet, primarily consisting of plant matter found in and around wetlands. Understanding the specific components of their diet, from roots to insects, is fundamental to appreciating their behavior and the conservation efforts aimed at restoring their populations. This feeding strategy shapes their habitat preferences and migratory patterns.
The Primary Diet: Aquatic Plants and Tubers
The foundation of the adult Trumpeter Swan’s diet is submerged aquatic vegetation (SAV), making them overwhelmingly herbivorous. Swans use their strong bills and long necks to graze on the leaves and stems of plants growing underwater in shallow lakes and marshes. They consume a wide variety of these plants, including pondweeds like Potamogeton, sedges, and muskgrass (Chara spp.).
Swans often dig into the muddy substrate beneath the water to extract roots, rhizomes, and tubers. Tubers, such as those from sago pondweed (Potamogeton pectinatus), are highly nutritious and a sought-after food source. These starchy reserves are important for building fat reserves necessary for surviving harsh winters and fueling migrations. Due to the sheer volume of vegetation required, swans spend a significant portion of their day foraging.
Dietary Needs of Cygnets (Juveniles)
The diet of young swans, known as cygnets, differs from adults to accommodate their rapid growth during the first few months of life. Cygnets require a high-protein diet to facilitate the development of their bodies and feathers. Therefore, their initial meals consist mainly of animal matter, which provides this necessary protein boost.
This invertebrate-rich diet includes small aquatic insects, crustaceans, and occasionally fish eggs or small fish. As cygnets mature, they begin a gradual shift away from this high-protein intake towards the herbivorous diet of their parents. This transition to a primarily vegetation-based diet is usually complete by about five weeks of age, though they may continue to supplement with small invertebrates for a longer period.
Seasonal Changes and Foraging Techniques
Trumpeter Swans employ specific foraging techniques that allow them to reach their submerged food, the most common being “upending” and “dabbling.” Upending involves tipping the body forward with the tail pointing upward, allowing the swan’s long neck to reach the bottom substrate in waters up to four feet deep. This method is used to access the roots and tubers buried in the mud.
Dabbling is a surface feeding behavior where the swan grazes on floating or emergent vegetation without submerging its body.
When aquatic habitats freeze over in winter, swans must alter their feeding habits and seek out terrestrial food sources. During this time, they move to agricultural fields to consume waste grains, such as corn and barley. They also graze on grasses and winter wheat. This seasonal flexibility allows many populations to survive in areas where open water is not available year-round.