Species Account: Brant Goose (Branta Bernicla)

Nomenclature

The Brant (Branta Bernicla) species is part of the goose family. It is divided into three extant subspecies: Dark-bellied Brant (B. b. bernicla), Pale-bellied Brant (B. b. hrota), and Black Brant (B. b. nigricans). According to DNA analysis, these species are genetically distinct and have interbreeding populations, supported by their variation of geographical range and migration patterns (Lewis et al. 2013). The Black Brant (B. b. nigricans) is the only official subspecies of Brant to occur in the Pacific Northwest, however recent genetic research proposes that a fourth subspecies, known as the Gray Brant, is present in the pacific northwest during the winter (Lewis et al. 2013). 

Status

The Brant species is widely established across Europe, Canada and North America. According to the most recent IUCN Red List Report in 2016, they are designated as a least concern species (IUCN 2016). They are protected under the Migratory Bird Treaty Act in the USA, which protects specific migratory birds from being sold, hunted, or exported unless under Federal permit. As of 2016, the Audubon society listed the Brant Goose as a climate threatened species (Kaufman 2016).

Distribution

The Brant species and its three subspecies are found across the northern hemisphere. Their vast migratory range allows them to occupy areas on the west and east coasts of the Americas, the Arctic, Russia, Germany, France, England and Greenland (Kaufman 2016). Within the Americas, they migrate between the low Arctic south down to the Puget sound. In some cases, they have been found migrating as far south as Baja, Mexico. In the pacific northwest, the Black Brant and Grey-bellied species are the only ones present on the Washington coast in the winter. They are a coastal species, commonly found in inland marine, freshwater and terrestrial environments. Specifically located in estuaries, wetlands, salt marshes, mudflats, and sand shores (Lewis 2016).

Figure 1. Geographical distribution of non-breeding Brant in the Pacific Northwest.

Description

The Brant is commonly misidentified as the Canadian goose because of their geographical range and habitat, however there are many differences between the two. The Brant is much smaller and darker than the Canadian Goose. It is approximately 55-56 cm in total length and has a wingspan of 106-121 cm. On average, this goose can weigh between 1.9-4.9 pounds during adulthood. They have a dark brown-gray body with white patches of feathers on the underside and sides of its body. They are grayish black on top of their body and snow white on the bottom of their body. Another key indicator is that their tail is much shorter than other goose species. The adults and juveniles both have black heads and beaks, but mature adults are distinguished by their white neck band and white scaling on their back (Marcel et al. 1998).

Figure 1. Adult Brant bird distinguished by its white neck band.

 Abundance

The current population of this species is currently unknown (BirdLife 2016). The global population of these birds ranges from 560,000-650,000 individuals. There is uncertainty in their population because some populations are increasing and stable, while others are decreasing. North American populations have experienced a slight increase in population in the past 40 years but this growth is statistically insignificant (BirdLife 2016). It is estimated that the Black Brant species has an average population of 130,000 individuals - indicating that this population is stable.  Studies suggest that reduced food supplies due to climate change, invasive species, hunting, urbanization and agricultural developments may impact their populations in the future (Lewis et al. 2013).

Reproduction

 The breeding season can last up to 3 months and begins in June when weather conditions are favorable. In the northern hemisphere summer, they breed in the arctic and in Alaska. When they arrive at their breeding sites, female Brant geese will nest in shallow depressions in the ground with down, moss, and grass to lay her eggs. The female Brant Goose reaches sexual maturity at 2-3 years of age. On average, females lay between three to five eggs in June and she will keep them protected for 24-26 days until they fully develop. Approximately 40 days after hatching, Brant geese will fledge to prepare for migration. Meanwhile, the male Brant geese will stay close to the female nesting site to protect his partner from predators like Arctic fox. Brant geese are monogamous and will raise their offspring together. They commonly will remain together and migrate to same breeding site every year to mate.

Feeding Habits

The Brant goose primarily survives on a plant-based diet. They forage for food in groups along coastlines, in shallow waters and along tidal flats. Their migratory patterns have a big influence their diet seasonally. During their winter migratory journey to the arctic, they consume a marine diet of green algae, seagrass, sea lettuce, wigeon grass, and rock grass, but prefer eelgrass when available (Kaufman 2016). In terrestrial environments, they consume sedges, pondweed, and grass.  Rarely, they will eat aquatic insects, worms and mollusks. These foods are found in intertidal zones along the coastline. In the summer, Brant geese can be found in salt marshes and in freshwater lakes eating moss and sedges.

Mortality

The average lifespan of an adult Brant is 28 years. The major causes of death for this species are sport and subsistence hunting, habitat loss, and reduced forage. They are especially vulnerable to mortality as they travel back from the extreme conditions in the arctic and are weakened by under-nutrition, travel and weather. Another source of mortality is the loss of eelgrass due to the reduction of wetland habitat and disease. They are vulnerable to chemical pollution entering estuaries from ships, urban sources, and agricultural runoff. One of their primary predators is the Arctic fox (Alopex lagopus) which preys on Brant when they nest and breed along the arctic coast. Male Brant use a defense strategy to protect females from predators. They stretch their neck forward, horizontal to the ground, and march displaying their size and their bright neck feathers. This is used to ward off predators during both the mating and nesting season.

Behavior

Unlike Canadian geese, the Brant does not travel in a V shaped flying group. They fly together in a clustered, unorganized group. When they land, they tend to herd in tightly packed groups or in paired groups of two. These groups can be fairly large and can include a few thousand birds per flock, however it is uncommon to see them gathered in groups bigger than a thousand. 

Habitat Use

The Brant goose spends a large portion of its lifetime flying from one destination to the other, sometimes up to 3,000 miles per year (Lewis et al. 2013). The Black Brant goose migrates up to the coastal arctic tundra to breed. When the breeding season is over, they migrate southwards to the pacific northwest coast. When breeding in the low arctic, they tend to nest in areas near salt marshes where there is protection from predators. They are also found nesting in grassy meadows, deltas, river valleys, and near lakes. They primarily nest along the coastline and on arctic islands, but they can be found 30 km inland (Birdlife International 2016). When they migrate southwards during the wintering season they gather near the coastline around estuaries, wetlands, salt marshes, mudflats, and sand shores. During this time, they seldom travel inland to eat coastal grasses and cereal grains.

Conservation

Actions to mitigate the impact of habitat degradation has been emphasized by countries such as Mexico, Canada, and the USA. Regulations to limit hunting and trapping in Alaska and Canada have been implemented. Pesticide and contaminant pollution legislation has been implemented to reduce the influx of toxins entering watersheds from agricultural and urban sources (Lewis et al. 2013). Since the initial protection of Brant geese in the 1930s, under the Migratory Bird Treaty Act, research and conservation efforts to protect eelgrass populations has been critical for protecting the Brant species. The conservation of Brant under the Migratory Bird Act was due to a massive die-off of eelgrass along the east coast of the US. The Migratory Bird Treaty Act has been used to legitimize the conservation of estuary, wetland, and salt marsh habitats from urban development (Migratory Bird Treaty Act 2013). Some parks along the coast in British Columbia, Canada have implemented a “no dog” policy in public parks during the Brant wintering season to decrease waste pollution and stress by dogs.

Climate Change

Their northern habitats are projected to expand significantly as the climate warms (BirdLife 2016). The winter habitat of Black Brant (B. b. nigricans) in the pacific northwest is expected to expand significantly northwards into Canada and Alaska (Kaufman 2016). Because of their highly specific diet and foraging patterns, the amount of food available may be reduced with changing climatic conditions and irregular seasonality. The die off of eelgrass populations along the coastal areas in the 1930s and impact on Brant geese is an indicator of the integral connection of this species to coastal eelgrass habitats. As eelgrass populations continue to decrease due to coastal development and agricultural pollution, Brant species will soon have to change their eelgrass diet and look for other safe wintering habitats (Rasumussen 1977). Without protection and preservation of wetlands, estuaries and salt marshes habitat, Brant populations will experience additional stress from foraging. Though 42% of their winter habitat range is to remain stable with climate change, the abundance of food will be the limiting factor that will affect the future of this species (Kaufman 2016).

References

BirdLife International 2016. Branta bernicla. The IUCN Red List of Threatened Species 2016: e.T22679946A85966135. http://dx.doi.org/10.2305/IUCN.UK.2016-3.RLTS.T22679946A85966135.en. Downloaded on 07 November 2018.

 Ganter B (2000) Seagrass (Zostera spp.) As food for brent geese (Branta bernicla): an overview. Helgoland Marine Research, 54, 63–70.

Kaufman, K. (2016, March 03). Brant. Retrieved November 6, 2018, from https://www.audubon.org/field-guide/bird/brant.

Lewis, T. L., D. H. Ward, J. S. Sedinger, A. Reed, and D. V. Derksen (2013). Brant (Branta bernicla), version 2.0. In The Birds of North America (A. F. Poole, Editor). Cornell Lab of Ornithology, Ithaca, NY, USA.

North American Bird Conservation Initiative. 2014. The State of the Birds 2014 Report. US Department of Interior, Washington, DC, USA.

Marcel Dekker, New York. Reed A, Ward DH, Derksen DV et al. (1998) Brant (Branta bernicla). In: The Birds of North America, Vol. 337 (eds Poole A, Gill F), The Birds of North America, Inc., Philadelphia, PA.

Migratory Bird Treaty Act. (2013, December 2). Retrieved from https://www.fws.gov/birds/policies-and-regulations/laws-legislations/migratory-bird-treaty-act.php

Rasmussen E (1977) The wasting disease of eelgrass (Zostera marina) and its effects on environmental factors and fauna. In: Seagrass Ecosystems – A Scientific Perspective (eds McRoy CP, Helfferich C), pp. 1–51.