Geese are predominantly herbivorous waterfowl, but they consume insects as a regular part of their diet. While the bulk of their nutrition comes from plant matter, small invertebrates provide a necessary supplement to their overall intake. This omnivorous behavior allows them to thrive in various environments by capitalizing on available food sources. This opportunistic feeding is tied directly to their seasonal biological needs and the nutritional demands of growth and reproduction.
The Predominantly Herbivorous Diet
Geese are highly efficient grazers, with their diet primarily composed of various plant materials. They use their strong, serrated bills to efficiently tear off grass shoots and leaves from the ground. Fresh grasses, such as fescue, bluegrass, and ryegrass, make up a significant portion of the adult goose’s food intake.
When foraging near or in water, they also consume aquatic vegetation like submerged pondweeds, duckweed, and the roots of cattails. This fibrous plant matter is processed through a digestive system adapted to ferment the tough cellulose. Plant material constitutes over 90% of the typical goose diet throughout the year.
Nutritional Necessity: Why Geese Seek Protein
The consumption of insects, though secondary to grazing, serves an important metabolic purpose. Geese seek out protein-rich invertebrates to meet elevated nutritional demands that their typical plant diet alone cannot satisfy. Protein is particularly crucial during the breeding season, when females require it for the production of eggs.
The need is most pronounced for hatchlings, known as goslings, who undergo a period of extremely rapid growth. Goslings require a diet with a much higher protein concentration than adults, sometimes needing up to 22% crude protein in their early weeks. This high-protein intake supports muscle development, feather growth, and overall structural integrity as they quickly mature. Adult geese also rely on this protein boost during the annual molting period, when they replace their flight feathers.
Specific Invertebrate Prey and Foraging Techniques
Geese consume a wide variety of small, soft-bodied invertebrates, focusing on items that are easily found while they are already foraging for plants. Common prey includes:
- Insect larvae
- Small crustaceans
- Earthworms
- Snails and slugs
- Terrestrial insects like beetles, ants, and grasshoppers encountered while grazing in fields
In aquatic habitats, geese employ a technique called dabbling, dipping their heads into shallow water to filter out aquatic insects and their larvae, such as those from mayflies and caddisflies. They also engage in a behavior known as grubbing, where they use their bills to probe and pull up food from soft mud or soil. This action dislodges and exposes hidden prey like worms and subterranean insect larvae.