An unmistakable small, black goose, the brent goose (Branta bernicla) is exceptional amongst geese for its strong, efficient flight, which carries it extraordinary distances of several thousand kilometres as it migrates after breeding in the Arctic (3)(4). Around the size of a mallard (Anas platyrhynchos), this diminutive goose has a short neck, and a small head and bill borne on a plump body (5). From a distance it looks all dark apart from the gleaming white under-tail, but is in fact typically grey-brown on the back with a small white neck patch (6). The male and female brent goose are similar in appearance, although the male is usually slightly larger and tends to have a broader neck patch (3)(4).
There are currently three recognised subspecies of the brent goose, each of which have a black head, bill, breast, tail and legs, but vary primarily in the colour of the belly and sides. The light-bellied subspecies (Branta bernicla hrota) has pale brown to whitish sides that are much lighter than the upperparts, the black brent (Branta bernicla nigricans) has a black belly with contrasting white sides, as well as a broader white neck patch, and the dark-bellied subspecies (Branta bernicla bernicla) is largely dark grey-brown, with little contrast between the upperparts and underparts (3)(4). The brent goose typically flies in tight, highly manoeuvrable groups, and is able to achieve remarkable speeds of up to 99 kilometres per hour as its beats its large, narrow wings very rapidly (3).
Before leaving for northern breeding grounds from mid-March, male brent geese display to spectating females, with birds choosing a partner on the basis of the similarity of the their white neck collars. At the breeding grounds, the brent goose may nest in dense colonies or more sparsely distributed pairs, with a shallow depression created on the ground and lined with feathers and vegetation for the clutch of three to five eggs. Both birds aggressively defend a territory around the nest by chasing intruders and by using threatening postures, which involve puffing the neck feathers out so that the white collar appears to surround the bill and head. The clutch of eggs is incubated for around 24 to 26 days whilst the adult birds moult and enter a flightless stage. The chicks hatch almost simultaneously and are then lead to feeding grounds by the adult birds, where they may feed for up to 13 or 14 hours each day, until they are ready to fledge at around 40 days of age. The brent goose reaches sexual maturity at 2 to 3 years of age and has a life expectancy of up to 28 years (2)(4)(8).
As a mainly herbivorous species, the brent goose feeds on a variety of vegetation, with eelgrass (Zostera marina) being a favoured food, although animal matter such as fish eggs, worms and snails is also consumed (8). The brent goose may graze on vegetation while walking on land or on exposed beds of aquatic plants, or while dipping its head underwater or upending its whole body while swimming to feed on submerged vegetation (2)(3).
The brent goose is found throughout the northern hemisphere, breeding in the Arctic during the summer before migrating southwards in advance of winter. At its breeding grounds it occurs in several distinct populations, each with different migratory patterns. The dark-bellied subspecies (Branta bernicla bernicla) mainly breeds on Taymyr Peninsula, Russia, and migrates to Denmark, the Netherlands, Britain and France, while the black brent (Branta bernicla nigricans) breeds from extreme north-eastern Siberia to north-central Canada and mainly winters down the Pacific coastline of North America, from Alaska south to Baja California, as well as Japan and Kamchatka, Russia. The light-bellied subspecies (Branta bernicla hrota) breeds in the eastern Canadian part of the high Arctic, northwest Greenland and Spitsbergen, and winters on the Atlantic coastline of North America or in Denmark, Ireland and north-east England (2)(3)(4)(7).
The brent goose breeds within coastal Arctic tundra, on or close to wet meadows with an abundance of low grassy vegetation. In the low Arctic, the species tends to nest in colonies near the upper edges of salt marshes on gently sloping coasts, but may also build its nests on grassy islands in ponds or deltas so as to protect its nest from predators, such as the Arctic fox (Alopex lagopus). In the mid- and high-Arctic, however, the brent goose is more sparsely distributed as the habitat is less suitable for breeding, with most nests built near river valleys, deltas or inland lakes, occasionally as far inland as 30 kilometres (3)(4)(8).
Before beginning its arduous southward migration, the brent goose gathers at staging areas in shallow marine waters, along shorelines, within lagoons, or behind sheltered beaches. Within its wintering range, this species becomes more closely associated with coastal habitats, and is most commonly found around estuaries, tidal mudflats, sand shores, salt marshes or in shallow muddy bays. During this period, the brent goose may also travel marginally inland to graze on coastal grasslands and cereal fields (3)(4)(8).
Despite being an abundant species that is not immediately threatened with extinction, the brent goose is vulnerable to hunting for food and sport, particularly after periods of cold weather when many birds are weakened and starving. Great reductions in numbers occurred during the 1970s when hunting pressure was greatest and there were no limits on catches in many parts of the species’ range. Protection from or the regulation of hunting has since allowed the brent goose to largely recover, with the global population numbering between 400,000 and 500,000 in the 1980s, although it may still be persecuted by farmers due to its habit of grazing in cereal fields. The brent goose is also vulnerable to reductions in food supplies following outbreaks of a disease that kills back eelgrass, which is a favoured food of the brent goose. Following an outbreak of this disease in the early 1930s, the black brent population crashed by 90 percent and did not recover until the mid-1950s. The brent goose is also threatened by disturbance and pollution from shipping and by chemical runoff from agricultural lands adjacent to estuaries (2)(3)(4)(8).
The existence of numerous, distinct breeding populations complicates the conservation of the brent goose as, while some populations are abundant and well protected, others are rare and have received little attention. Those populations wintering along the coasts of North America, for example, are managed cooperatively by Canada, the U.S. and Mexico, and studies are conducted into the size, distribution and trends of the populations, with regulations set for harvesting. In contrast, very little is known about populations in eastern Russia. It is recommended that brent goose populations are monitored so as to allow the careful regulation of hunting levels, as populations tend to fluctuate with harsh weather conditions (2)(3)(4). The brent goose is also protected in a number of reserves (5).
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