Pale-bellied brent geese

Bird of the Month February 2023: Brent Goose

February is a good month to see our smallest goose, the brent, or brant. This diminutive species is about the same size as a mallard and much smaller than its greylag and pink-footed cousins. In the winter, the UK and Ireland host two distinct subspecies, or races. These are split between a number of traditional coastal sites, with some holding thousands of birds each winter. By April, many will be heading off to their Arctic breeding grounds, so be sure to catch up with them before it is too late!

The Burnt Goose

The name ‘brent’ comes from the Norse word ‘brand’ which means burnt or black. It is easy to see why Scandinavians used this name. Much of the brent goose’s upper body is a dark greyish brown that looks like burnt charcoal. Their head and neck is black apart from small white patches on either side of the neck. They have an undeniably ‘cute’ face. Two subspecies winter in the UK and Ireland: dark-bellied and pale-bellied. Dark-bellied brents, as the name suggests, have bellies that are almost the same colour as their backs. Pale-bellied birds have paler grey bellies. Both have a bright white undertail and short, dark tails. These two subspecies breed and winter in separate locations from each other (more on this later). This means that if you are in any doubt as to which you are seeing, your location should confirm one way or the other.

Pale-bellied brent geese
Brents are our smallest goose

All the British and Irish wintering birds favour coastal sites, whether estuaries or saltmarshes. Unlike many geese, they don’t tend to fly in V-shaped skeins but form loose lines or groups as they move about. Their preferred food is eelgrass, an extremely important plant around our coasts. This seagrass provides food for many species, shelter for others, stabilises the seabed and captures large amounts of carbon. At sites with lots of geese, by mid to late winter the eelgrass can become severely depleted. At this point birds will move onto nearby fields to feed, including playing fields and golf courses. In Ireland, the Dublin Bay population has taken to this particularly well and the geese have become extremely habituated to humans as they feed on grassy areas near dog-walkers and playing children. Birders can get incredible views of the birds as a result.

Different Strokes for Different Folks

Most taxonomists recognise three different brent goose subspecies. A few people would even go as far to suggest they are full species. All have fairly distinct breeding and wintering areas from each other. Pale-bellied brents breed in Svalbard, Franz Josef Land, Greenland and Eastern Canada. The Svalbard and Franz Josef birds, along with a small proportion of the Greenland birds, winter in Denmark and around Lindisfarne in Northumberland. Small groups of birds also winter in Scotland. Around 35,000 birds from the Canadian and Greenland populations winter around the island of Ireland, with many on Strangford Lough and around 7,000 in the Dublin Bay area. An increasing number of birds winter in northern Iberia.

Brent geese
Pale-bellied brents have a silvery grey belly contrasting with their darker backs

Dark-bellied brents, meanwhile, breed in Siberia. Approximately 90,000 birds of this subspecies winter around the UK from the Humber on the east coast around to the Exe Estuary on the south. There are big concentrations on the Wash and North Norfolk coast, estuaries in Essex, the Thames Estuary and Chichester. A third subspecies is called the black brant. This is overall a much darker bird than its two relatives, but with a very obvious white flank patch and a much bigger white area on the neck. These birds breed in Russia’s far east, Alaska and western Canada. Most winter along eastern Pacific coasts as far south as Mexico, with some on western coasts in Japan, Korea and north-eastern China. A few individuals turn up in Britain and Ireland each winter, so they are worth looking out for.

Dark-bellied brent geese
As their name suggests, dark-bellied brents have darker undersides

Along with these three subspecies, some birders have suggested a fourth exists, dubbed the grey-bellied brent. A population of birds breeding on the Parry Islands in Canada’s high Arctic appears intermediate in colour between dark and pale-bellied birds. They winter around Puget Sound near Seattle. The colouration and distinct breeding and wintering grounds has prompted some to suggest it is a separate subspecies, but not everyone agrees. Possible grey-bellied brents also get reported most years in the UK and Ireland.

Possible grey-bellied brents
These two birds were reported as possible grey-bellied brents due to their intermediate characteristics

Masters of Migration

Brent geese are the most northerly breeding geese in the world. They breed on the Arctic tundra in an almost complete circle around the northern polar region. Some nests have been recorded just 500 miles from the North Pole. This means that they carry out an extraordinary migration each year, to and from their breeding and wintering grounds. Irish wintering birds may travel around 10,000 kilometres every year, a staggering distance. Even populations with a shorter migration route, such as those moving between Lindisfarne and Svalbard, will cover approximately 5,000 kilometres a year. Given that brents live for about 19 years on average, some may travel over 200,000 in their lifetimes. This video produced by a research team at the University of Exeter is well worth a watch to get a real sense of the scale of this achievement.

Brent geese
Saltmarshes are a common winter habitat for brent geese

So, how do they manage all this? One important factor is that the journey north does not take place in one go, and birds will stop off to feed up on the way. The breeding grounds don’t thaw sufficiently until early June, and this means they have time to do this without missing out on the chance to breed. Birds will typically increase their weight by 40 – 50% during these stopovers. Not only does this intense feeding fuel the next stage of the journey, but it also sustains them for a time when they arrive on the breeding grounds. There is often little food when they first get back to these semi-frozen landscapes. Birds travelling from the UK and Ireland to Canada stop off each year in Iceland. Birds heading east to Svalbard or Russia have a staging post in the Baltic region.

Climate Wins and Losses

The Earth’s polar regions are warming disproportionately quicker than elsewhere. How this will affect brent geese in the future is not as straightforward as a simple good or bad outcome. A study in 2014 found that black brants, on one level at least, were benefitting from climate change. As more saltmarshes formed where previously there would be year-round sea ice or permafrost, the geese were finding a greater expanse of suitable habitat to carry out their annual moult in. Moulting requires a lot of energy and also leaves birds vulnerable to predators. As a result, moulting sites need to be food-rich and have safe open water areas. The researchers found more of these areas opening up in coastal Alaska.

Brent geese
Climate change is having an impact on eelgrass, a favourite winter food

The flip side is that as more polar areas stay ice-free, more human activity can take place in previously unreachable locations. Coal, oil and mineral deposits that humans could not access before will become increasingly accessible. Exploitation of this kind may well destroy the geese’s tundra breeding grounds. There are other possible consequences too. Polar bears are increasingly predating the eggs of various goose species, including snow and barnacle geese. This is almost certainly due to them finding it harder to hunt seals from the sea ice as it shrinks. Bears now have to spend more time on land and this overlaps more with the geese’s breeding season. Brent geese may well be targeted, as well, either now or in the future. Climate change is also impacting seagrass, a vital food source in the winter months.

The Diminutive Goose

There is nothing quite like the sound of hundreds of brent geese chatting to each other as they feed on a saltmarsh or fly overhead. Our smallest goose is a charming and wonderful feature of winter birding at many coastal sites. I, for one, hope to see them a few more times this year before they head off again on that amazing migration to the Arctic.

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