The lesser scaup (Aythya affinis) is a small North American diving duck known for its blue bill and habit of diving to find food. Lesser scaups are omnivorous and have a diverse diet consisting of aquatic plants, mollusks, crustaceans, insects, and small fish. Their feeding habits allow them to thrive on lakes, rivers, ponds, and wetlands across much of North America.
Aquatic Plants
Aquatic plants make up a significant portion of the lesser scaup diet. Scaups will readily feed on the leaves, stems, roots, and seeds of a variety of aquatic vegetation. Some of the most commonly consumed aquatic plants include:
– Wild celery (Vallisneria americana) – Abundant in shallow, freshwater habitats. Provides leaves, stems and seeds.
– Sago pondweed (Stuckenia pectinata) – Valued for its narrow leaves and small, hard seeds. Widespread across North America.
– Horned pondweed (Zannichellia palustris) – Grows in shallow water. Seeds and foliage eaten.
– Eurasian watermilfoil (Myriophyllum spicatum) – Invasive species in North America. Scaups eat the foliage and soft stems.
– Wild rice (Zizania palustris) – Important food source, providing protein-rich seeds.
– Duckweeds (Lemna minor) – Small floating plants eaten whole.
– Widgeon grass (Ruppia maritima) – Provides foliage and seeds, especially in brackish waters.
Benefits of Aquatic Plants
Aquatic plants provide lesser scaups with carbohydrates for energy and fiber for digestion. The plants also supply protein for growth and development. Diving ducks like scaups have expansive body musculature to propel them underwater while foraging. The protein from aquatic vegetation helps maintain their muscle mass. Fiber aids digestion and prevents intestinal issues that can be problematic in waterfowl.
Mollusks
Lesser scaups use their specialized bills to forage for mollusks in shallow waters. Some mollusk species commonly eaten include:
– Snails (class Gastropoda) – Scaups will eat small snails whole. Larger snails have their soft body pulled out of the shell.
– Freshwater clams (family Unionidae) – Scaups pry open the shells to access the soft tissue inside.
– Fingernail clams (family Sphaeriidae) – Abundant small clams eaten whole.
– Zebra mussels (Dreissena polymorpha) – Invasive mollusk that scaups have learned to exploit as a food source.
Benefits of Mollusks
Mollusks offer an excellent source of protein for building muscle and replenishing energy reserves after migration. Snails and clams provide healthy fats as well in the form of omega-3 fatty acids. The shells contribute calcium and other minerals to help meet the ducks’ nutritional requirements for bone health and growth.
Mollusk | Size | Habitat |
---|---|---|
Snails | 0.1 – 2 inches | Shallow freshwater |
Freshwater clams | 0.5 – 4 inches | Lakes, rivers, streams |
Fingernail clams | 0.1 – 1 inch | Lakes, ponds, wetlands |
Zebra mussels | 0.5 – 1.5 inches | Lakes, rivers, estuaries |
Crustaceans
Lesser scaups forage on small crustaceans swimming through shallow waters or buried in bottom sediments. Common crustacean prey includes:
– Freshwater shrimp (order Decapoda) – Scaups eat both adult shrimp and larvae. Provide protein.
– Crayfish (family Astacidae) – Scaups will eat juveniles whole and remove meat from larger crayfish.
– Scuds (order Amphipoda) – Abundant in lakes and streams. Eaten whole.
– Isopods – Aquatic relatives of terrestrial pillbugs. Consumed whole.
Benefits of Crustaceans
Like mollusks, crustaceans give scaups a boost of protein for muscles and energy. Exoskeletons provide calcium for bone health. Crayfish are especially high in vitamin B12, which aids metabolism. The omega-3 fats in some crustaceans help scaup ducklings develop healthy brains and bodies.
Crustacean | Size | Habitat |
---|---|---|
Shrimp | 1 – 5 inches | Lakes, ponds, rivers |
Crayfish | 2 – 6 inches | Freshwater lakes, streams |
Scuds | 0.1 – 1.5 inches | Lakes, ponds, wetlands |
Isopods | 0.1 – 0.5 inches | Lakes, streams, marshes |
Insects
Lesser scaups will eat a variety of insects when the opportunity arises. Common insect prey includes:
– Mayfly larvae (order Ephemeroptera) – Abundant in bodies of freshwater. Nutritious food source.
– Caddisfly larvae (order Trichoptera) – Live in self-built cases, which scaups ingest whole.
– Dragonfly larvae (order Odonata) – Caught while scaups are diving and foraging.
– Water boatmen (family Corixidae) – Aquatic insects swimming near surface.
Benefits of Insects
Insects give scaups added protein and fat when other prey may be harder to find. The larvae of mayflies, caddisflies, and dragonflies are especially packed with nutrients to fuel growth before adulthood. Easy catches for opportunistic scaups.
Insect | Size | Habitat |
---|---|---|
Mayfly larvae | 0.1 – 1 inch | Lakes, ponds, rivers |
Caddisfly larvae | 0.1 – 1 inch | Lakes, rivers, streams |
Dragonfly larvae | 0.5 – 2 inches | Freshwater ponds, marshes |
Water boatmen | 0.1 – 0.5 inches | Lakes, ponds, wetlands |
Fish
Lesser scaups will eat small fish that they can swallow whole while diving and foraging. Some fish commonly eaten include:
– Minnows (family Cyprinidae) – Abundant prey in freshwater habitats. High in omega-3s.
– Sticklebacks (family Gasterosteidae) – Spines swallowed by scaups when eaten whole.
– Sunfish (family Centrarchidae) – Small individuals eaten whole.
Benefits of Fish
Fish provide scaups with a good source of protein, healthy fats, and minerals like iodine and selenium. The omega-3 fatty acids in many fish support brain and vision development in ducklings. Small bones contribute dietary calcium and phosphorus.
Fish | Size | Habitat |
---|---|---|
Minnows | 1 – 5 inches | Lakes, ponds, streams |
Sticklebacks | 1 – 3 inches | Lakes, streams, estuaries |
Sunfish | 2 – 10 inches | Ponds, lakes, rivers |
Seeds
In addition to the seeds of aquatic plants, lesser scaups will eat seeds from certain wetland and agricultural plants. These include:
– Wild millet (Echinochloa sp.) – Abundant grass seeds in marshes and mudflats.
– Rice – Domestic and wild rice eaten when found.
– Corn – Will eat waste corn seeds in agricultural areas.
– Soybeans – Opportunistically forage on waste soybeans after harvest.
Benefits of Seeds
Seeds give scaups concentrated nutrition in the form of carbohydrates, protein, and fiber. They are energy-rich foods. The fiber aids digestion, while the minerals in seeds contribute to bone density. Soybeans and corn provide added fat and protein.
Seed | Size | Habitat |
---|---|---|
Wild millet | 0.1 inch | Marshes, wetlands |
Rice | 0.25 inch | Agricultural areas |
Corn | 0.2 – 0.5 inch | Agricultural areas |
Soybeans | 0.25 – 0.5 inch | Agricultural fields |
Grit
Lesser scaups will also deliberately ingest grit – small pebbles, gravel, sand, and other hard, inorganic particles. They swallow these to store in their muscular gizzard, located between the esophagus and small intestine. In the gizzard, food is ground against the grit to aid digestion.
Benefits of Grit
The grit helps scaups mechanically break down food for better nutrient absorption. This allows them to make use of a wide variety of plant and animal foods in their diet. The abrasive action of grit grinding food also helps stimulate gut motility to prevent intestinal problems.
Digestive Adaptations
Lesser scaups have a number of digestive tract adaptations to make use of their diverse diet:
– Muscular gizzard with grit to grind food
– Long small intestine for nutrient absorption
– Bacteria and protozoans to help break down cellulose from plants
– Ability to discard inedible parts through their cloaca
– High metabolism to generate heat and energy from food
Dietary Flexibility
Their diverse diet and digestive adaptations allow lesser scaups to take advantage of many different aquatic food sources. This gives them dietary flexibility across a range of freshwater habitats and through seasonal changes in food availability. It also allows them to shift away from depleted food resources to more abundant options. This helps scaups survive and thrive across large geographic ranges.
Foraging Behavior
Lesser scaups employ particular foraging behaviors and strategies while diving and feeding:
– Diving underwater to find food – can reach depths up to 60 feet
– Using bill to grab food while swimming and dipping head
– Consuming small food items whole
– Tearing larger prey into bite-sized pieces
– Gulping air before diving to increase buoyancy
– Foraging mainly during daylight hours
– Forming large feeding flocks – reduces competition
Diving Advantage
Their diving ability allows scaups to access food resources unavailable to dabbling ducks. Submerged aquatic plants, mollusks, and other prey can be exploited. Excellent underwater vision enhances their foraging success while diving. Flock feeding reduces intraspecific competition.
Ideal Foraging Habitat
Lesser scaups preferentially forage in areas with certain characteristics:
– Abundant aquatic vegetation
– Muddy or sandy bottoms – house bivalves and other invertebrates
– Shallow water depths – make diving and finding food easier
– Slow currents – reduce energy spent fighting water movement
– Protected bays and inlets – provide calm water
Habitat Loss
Unfortunately, some of these productive foraging habitats are being degraded and lost due to human activities. Wetland drainage, shoreline development, and pollution all negatively impact scaup foraging areas. Conservation efforts are needed to preserve essential scaup feeding habitat.
Breeding vs Wintering Habitats
Lesser scaups use somewhat different habitats for breeding versus wintering:
Breeding Habitats
– Shallow lakes and marshes with emergent vegetation
– Abundant aquatic plants and invertebrates to feed females and young
Wintering Habitats
– Large lakes and estuaries with abundant mollusks
– Coastal bays and lagoons with shallow water
– Wetlands and flooded fields rich in plant seeds
Migration Stopover Habitats
During spring and fall migrations, lesser scaups rely on key stopover habitats to rest and feed, including:
– The Prairie Pothole Region – shallow marshes and ponds with abundant invertebrates
– The Great Lakes – large lakes with mollusk populations
– Major river systems – e.g. Mississippi, Ohio, Missouri rivers
– Coastal marshes and estuaries along migration routes
Threats
Loss and degradation of migration stopover habitat has been linked with scaup population declines. Conservation of remaining habitat is crucial.
Conclusion
In summary, the diverse diet of lesser scaups allows them to thrive across a wide range of freshwater habitats. They forage on aquatic plants, mollusks, insects, crustaceans, fish, and seeds. Their digestive system is adapted to make use of this varied diet. Key foraging habitats include shallow lakes, ponds, wetlands, and estuaries. Conservation efforts to preserve these essential habitats are needed to support scaup populations. Their dietary flexibility provides resiliency, but habitat loss poses risks. Understanding the feeding ecology of scaups can help inform management plans.