The barnacle goose (Branta leucopsis) is a medium-sized goose species that breeds in the Arctic regions of Greenland, Svalbard, Norway, and Russia. Barnacle geese are herbivores that eat a variety of plant materials including leaves, stems, roots, seeds, and berries.
Grasses
Grasses make up the bulk of the barnacle goose’s diet. They feed extensively on grasses while on their breeding grounds in the Arctic tundra during summer. The goose grazes on grasses like sedges, rushes, fescues, and bluegrasses. The succulent leaves and nutritious roots of grasses provide the birds with carbohydrates and protein.
Sedges
Sedges are grass-like plants from the family Cyperaceae that grow abundantly in wetlands. Barnacle geese consume various sedge species but prefer the leaves and roots of Carex sedges. Carex provide the geese with protein, minerals, and soluble carbohydrates. The birds favor Carex species like C. subspathacea, C. aquatilis, and C. stans in the low Arctic region.
Rushes
Rushes are another important food source for barnacle geese in the Arctic. They feed on the green leaves, stems, and shoots of rushes when grazing in coastal marshes and wet tundra. Some common rushes eaten include Juncus arcticus, J. biglumis, and J. trifidus. Rushes provide the geese with fiber, minerals like potassium and sulfur, and some protein.
Herbs
Herbaceous flowering plants commonly known as herbs are a supplementary food source for barnacle geese. They feed on herb leaves, shoots, seeds, and flowers of plants like chickweeds, plantains, nettle, sorrels, and buttercups. These Arctic herbs provide essential nutrients like beta-carotene, flavonoids, and vitamin C.
Shrubs
During nesting season, barnacle geese eat the leaves, flowers, and seeds of small Arctic shrubs. This provides them with abundant carbohydrates and protein. Some typical shrub species eaten include dwarf willow, Arctic willow, crowberry, bearberry, and heath species like Empetrum nigrum.
Roots, Stems, and Shoots
Barnacle geese dig up and consume the underground storage organs of plants like roots, rhizomes, tubers, corms, and bulbs. These provide them with carbohydrates, fat, and protein accumulated by plants. They also eat the stems and shoots of grasses and sedges. Calorie-rich stems and shoots enable the geese to quickly put on fat and protein.
Seeds and Berries
During late summer and autumn, barnacle geese feed on the nutritious seeds of grasses, sedges, and herbs. They also eat the berries of Arctic shrubs like blueberries, crowberries, bearberries, and cloudberries. Seeds and berries help the geese accumulate reserves for their long migration south.
Agricultural Crops
Barnacle geese fly south to temperate regions like Scotland, Ireland, and Norway for wintering. Here a major part of their diet consists of cultivated grass crops like winter barley, winter wheat, ryegrass, clovers, and potatoes. Feeding on these agricultural crops provides them with abundant carbohydrates.
How do barnacle geese find food?
Barnacle geese employ some clever tactics to locate optimal feeding grounds during their Arctic breeding season:
- They follow receding snow lines to find the first emerging vegetation.
- They gravitate towards wetlands and marshes where sedges, rushes, and herbs thrive.
- They seek south-facing slopes which clear of snow earlier.
- They nest close to feeding areas to minimize travel distance.
- They may nest in loose colonies to benefit from the combined knowledge of many geese.
During wintering and migration, barnacle geese make pit stops at sites along their known flyway to feed and refuel. They follow and memorize these routes each year.
How much do barnacle geese eat?
Barnacle geese spend over 80% of their time foraging and feeding. Here are some estimates of their daily food intake:
- Laying females consume 325-350 grams of food daily.
- Adults eat 300-325 grams per day during molting.
- Goslings may eat up to 150 grams per day.
- During spring and autumn migration, the geese eat 200-250 grams daily while flying substantial distances.
The actual amount of food eaten depends on factors like bird size, growth stage, activity level, and physiological demands. During summer, barnacle geese need to consume large quantities of nutritious vegetation to accumulate fat and protein reserves for migrating and winter survival.
What is the grazing behavior of barnacle geese?
Barnacle geese exhibit some typical grazing behaviors while feeding:
- They walk slowly while grazing with their heads down and necks extended.
- They steadily snip off and swallow small pieces of vegetation.
- They tend to graze in groups, with adults leading their goslings.
- They frequently engage in ‘head dipping’ – submerging their head underwater to graze on aquatic plants.
- They often rotate feeding sites within their breeding territory to prevent overgrazing any area.
Rotational grazing allows the geese to obtain nutritious regrowing plant shoots. It also ensures that they don’t completely deplete the vegetation in any section of the tundra.
How do barnacle geese digest their food?
Like other birds, barnacle geese have specialized digestive systems to process their herbivorous diet:
- In the esophagus, mucus moistens dry vegetation.
- The proventriculus secretes hydrochloric acid and digestive enzymes like pepsin to break down food.
- The gizzard grinds food into a digestible pulp.
- The small intestine absorbs nutrients into the bloodstream.
- The large intestine reabsorbs water from waste and forms fecal pellets.
- A cecum near the intestine’s junction ferments plant matter and produces nutrients.
Fermentation in the cecum allows barnacle geese to extract maximum nutrition from high-fiber vegetation. The entire digestion process takes just 2-4 hours from ingestion to excretion. This rapid throughput enables geese to keep eating frequently.
How do barnacle geese adapt their diet seasonally?
Barnacle geese show some seasonal adaptations in their diet:
Spring
- They eat residues of last season’s vegetation on arrival at breeding grounds.
- They switch to newly emerging shoots and leaves as snow melts.
- Females boost protein intake before egg-laying.
Summer
- They favor highly digestible greens, roots, and shoots.
- Goslings need high-protein diets for rapid growth.
- Adults eat sparingly during molting when flight feathers are shed.
Autumn
- They shift to high-carb and high-fat foods to accumulate migration reserves.
- Seeds and aquatic vegetation help build fat and protein stores.
Winter
- Agricultural crops provide carbohydrates.
- Protein requirements decrease once the geese stop flying for the season.
By switching up their diet, barnacle geese meet the changing nutritional demands across the year. Their dietary flexibility allows them to thrive across a range of Arctic and temperate habitats.
What adaptations help barnacle geese eat?
Barnacle geese possess some key anatomical and physiological adaptations that aid their herbivorous lifestyle:
- Serrated edges on their short black beak help cut and grip food.
- A long neck allows them to forage underwater.
- Distensible esophagus and expandable stomach help store food.
- Powerful enzymes break down coarse vegetation.
- A muscular gizzard grinds food particles.
- A long intestine absorbs nutrients from fibrous matter.
- Cellulose-digesting gut flora helps digest plant cell walls.
Additionally, barnacle geese have excellent eyesight to identify nutritious forage across vast Arctic landscapes. Their ability to fly long distances gives them access to varied feeding habitats.
Do barnacle geese face any dietary challenges?
Despite their adaptations, barnacle geese face some key feeding challenges:
- Short Arctic summers limit time to gain reserves.
- Low protein content in some plants provides insufficient nutrition.
- Incubating geese must fast while sitting on eggs.
- Poor weather can restrict access to food.
- Competition from other geese grazing on the tundra.
- Overgrazing near colonies can degrade vegetation.
- Climate change may alter plant communities and drying habitats.
During migration and wintering, barnacle geese also face potential shortages and disturbances to their agricultural food sources. Despite their challenges, barnacle geese continue thriving as clever foragers and highly adaptable herbivores.
Conclusion
In summary, the barnacle goose is a specialist herbivore feeding mainly on Arctic grasses, sedges, and herbs during breeding season. It switches to agricultural crops during wintering. The goose employs behavioral adaptations like rotational grazing and anatomical features like serrated beaks to maximizenutrition from its vegetarian diet. While facing challenges like short summers and climate change, the barnacle goose persists as a successful species by exploiting a flexible diet. Understanding the adaptations and flexibility of the barnacle goose diet provides wider insights into how specialist herbivores flourish in extreme environments.