In a new blog series, our Conservation Trainee Abi David explores some of the amazing creatures that call seagrass meadows their home. The Brent Goose Branta bernicla is of a similar size to a Mallard duck, making it one of the smallest goose species in the world. They are a
In a guest blog post for World Migratory Bird Day, our Solent Fieldwork Officer Emma Butterworth explores the role that seagrass plays for migratory birds: Every year, migratory birds embark on epic journeys—some spanning thousands of miles—between breeding and wintering grounds. These incredible migrations demand an immense amount of energy,
In a new blog series, our Conservation Trainee Abi David explores some of the amazing creatures that call seagrass meadows their home. The Brent Goose Branta bernicla is of a similar size to a Mallard duck, making it one of the smallest goose species in the world. They are a highly social species and form strong bonds within the groups they live in. If you spot a group of Brent Geese, look out for the ‘compass’ goose – this is the leader of the group and will lead the way between foraging areas. Depending on the species of Brent Goose, individuals may have a dark or light belly, along with a dark head and body, with adults having a small white patch on their necks. They can be seen throughout the UK during the autumn/ winter months in marine, intertidal or wetland areas. Dark bellied Brent Geese. Photo Credit Emma Butterworth Migration Just like many other bird species, Brent Geese carry out an annual migration. They spend summer months breeding and raising chicks in the Arctic and migrate to Western Europe for more temperate winters. Generally, the individuals we get overwintering here in the UK are from Siberia. Due to these long migration routes and small body size, Brent Geese have a high food demand meaning they heavily rely on stopovers to refuel. Their most popular stopover sites tend to be Zostera marina meadows. Large numbers of Brent Geese have been spotted for several weeks each year in Izembek Lagoon (Alaska), lagoons in Baja California, the German/Danish Wadden Sea, the Golfe du Morbihan (France), British estuaries, and the White Sea (Western Russian Arctic). Diet Brent Geese are heavily herbivorous and mainly consume seagrass. They have relatively short necks and lack the ability to dive so can only reach plants at low tide or in shallow water. Interestingly, during breeding season the geese will consume a wide range of plant species but show a strong preference for Zostera species throughout non-breeding seasons due to the high digestibility and nutritional value compared to other options. They have been observed eating both the leaves and rhizomes of the plants. Importance of seagrass for Brent Goose populations As mentioned previously, Brent Geese rely heavily on seagrass during their migrations. This can be seen in population trends. In the 1930s, Zostera species across the North American coast were heavily affected by wasting disease and there was a significant population decline. At the same time, a steep decline in Brent Goose population was also observed on both sides of the Atlantic, with estimates ranging from 75 – 90% of populations lost. During the 1950s, there was a good recovery of seagrass beds in the areas previously affected, which was followed by a recovery of Brent Goose populations from around 15,000 to over 100,000. Similar smaller scale events like this have been observed, showing just how important healthy seagrass meadows are for species like the Brent Goose that rely so heavily on them. Are Brent Geese bad for seagrass restoration? It could be argued that Brent Geese are bad for seagrass and bad for seagrass restoration due to their consumption of the plants. However, there is a bit more to it than that. Seagrass provides services for many species, and a food source is one of those. Anecdotally, there have been instances where restoration has occurred only for geese to come along and eat all of the freshly planted shoots, which really isn’t ideal. In the scientific literature, there is mixed evidence about how much the geese will consume and how this affects the meadow’s health, which makes it difficult to quantify their impact. Some research notes that the percent the geese eat out of the whole meadow is actually quite small and a healthy meadow should have no issue recovering from any damage. The geese could even be useful in seagrass restoration. They tend to only be seen where food is available and as such are an indicator species for the health of an ecosystem. Like all birds, they are useful for their ability to spread nutrients and seeds through their faeces, helping to spread plant species more widely than they would on their own. Additionally, they are an important food source for predators such as foxes and raptors in their Arctic breeding grounds. Brent Geese, like any other species using seagrass, are carrying out behaviours that have evolved over thousands of years. Therefore, the question of whether geese are bad for seagrass restoration is not a straightforward one. What do you think? Sources: Ganter, B. (2000). Seagrass ( Zostera spp.) as food for brent geese ( Branta bernicla ): an overview. Helgoland Marine Research, 54(2–3), 63–70. https://doi.org/10.1007/s101520050003 Find out more the role that seagrass plays for migratory birds here.
In a guest blog post for World Migratory Bird Day, our Solent Fieldwork Officer Emma Butterworth explores the role that seagrass plays for migratory birds: Every year, migratory birds embark on epic journeys—some spanning thousands of miles—between breeding and wintering grounds. These incredible migrations demand an immense amount of energy, which makes stopovers and overwintering sites crucial for survival. Stopovers are the rest stops of the bird world, where species can refuel, rest, and recover before continuing their journeys. Overwintering sites are at one end of the journey, where birds can survive over the harsher months. One foraging habitat for these globetrotters? Seagrass meadows. These marine plant communities don’t just benefit marine life—they play a surprising role in supporting migratory birds. Depending on the species and their needs, birds utilize seagrass in a few key ways. Some species, like certain wildfowl, feed directly on the seagrass itself. For example, brent geese (Branta bernicla) are well known for grazing on seagrass (Zostera spp.) which is their preferred food source. UK estuaries support around 100,000 overwintering brent geese, which arrive from Siberia, Svalbard, Canada and Greenland. These numbers represent around 40-50% of the European wintering population and around one fifth of the global population! Key wintering sites in the UK include Strangford Lough, Lindisfarne, Essex, and the Solent. Seagrass provides crucial food reserves to help them survive over winter and have enough energy to make the long return journey to their breeding grounds. Other birds aren’t after the plants, but the creatures living within them. Seagrass beds act as nurseries for juvenile fish and are home to a wide range of invertebrates like crabs, snails, and worms. Migratory shorebirds such as curlew, godwits (bar-tailed and black-tailed), dunlin, knot, and grey plover forage on these rich prey communities, finding food within the leaves and sediment. Redshank on seagrass. Photo Credit Emma Butterworth Dark-bellied brent geese. Photo Credit Emma Butterworth My own research focuses on understanding how UK birds are using seagrass habitats. The Convention on Migratory Species (CMS) encourages countries to develop inventories of migratory species that use seagrass meadows, and I am aiming to develop this inventory. So far, I have observed 18 species listed by the CMS foraging within seagrass meadows, and this is only the beginning! If you have observed any birds outside of those listed below, or if you have photographic evidence of any migratory species foraging within seagrass, please get in touch! We are especially interested in migratory birds but information on all birds is welcome! From a conservation perspective, this work matters. Seagrass meadows are among the most threatened ecosystems globally, facing pressures from coastal development, pollution, and climate change. As we learn more about the intricate connections between land, sea, and sky, it’s clear that conserving seagrass meadows is important to many aspects of nature—including our feathered visitors from far away. UK bird species listed by the Convention on Migratory Species that have been observed foraging on seagrass during surveys and fieldwork. brent goose, dark-bellied Branta bernicla bernicla brent goose, light-bellied Branta bernicla hrota mallard Anas platyrhynchos mute swan Cygnus olor shelduck Tadorna tadorna teal Anas crecca wigeon Mareca penelope bar-tailed godwit Limosa lapponica black-tailed godwit Limosa limosa curlew Numenius arquata dunlin Calidris alpina greenshank Tringa nebularia grey plover Pluvialis squatarola knot Calidris canutus redshank Tringa totanus common ringed plover Charadrius hiaticula sanderling Calidris alba turnstone Arenaria interpres whimbrel Numenius phaeopus Further information Unsworth, Richard & Butterworth, Emma. (2021). Seagrass Meadows Provide a Significant Resource in Support of Avifauna. Diversity. 13. 363. 10.3390/d13080363. https://www.mdpi.com/1424-2818/13/8/363 Convention on the Conservation of Migratory Species of Wild Animals, Aves https://www.cms.int/en/species?field_species_class_tid=421 Please contact Emma Butterworth with any “birds on seagrass” sightings: emmabutterworth@projectseagrass.org
