Bird of the Month June 2023: Gannet

The northern gannet is the UK’s largest seabird and is, in adult plumage at least, instantly recognisable. Although small numbers can be seen around our coasts in most months of the year, summer is the best time to catch up with them. This is because by June birds are back at their busy clifftop and island colonies and well and truly stuck into the breeding season. Seeing, hearing (and smelling!) these large, white birds, crowded together at this time of year is one of our greatest wildlife spectacles. Added to this is the chance to watch them perform their spectacular feeding dives. All of which makes them a worthy bird of the month for June.

Northern Giants

With their two metre wingspans, gannets are bigger than any other bird you are likely to encounter at sea in the North Atlantic, bar the odd misplaced albatross. Their largely white bodies also make them easy to spot at a distance. This may help them spot each other at sea and so find good places to fish. Gannet heads have a distinctive yellowy-cream wash. Their eyes are a pale greyish blue, surrounded by a brighter blue ring. They have long white wings with black tips.

Adult gannet
Adult gannets are white with cream heads and black wing tips

The bird’s Shetland dialect name, the solan, almost certainly comes from the Old Norse word sula. This refers to the cleft stick appearance of these black wing tips when folded. The word even appears in the names of some of their colonies, including the island of Sula Sgeir, literally ‘gannet skerry’. A long, pointed bill and dark feet offset by a line in green or blue up each toe complete the picture. Males and females are identical.

Young gannet
Juvenile gannets are dark brown with white flecks

Juveniles are a different proposition and the first time you see one you might not even think they are gannets. Once fledged they are dark brown all over with small white flecks at the tips of the feathers. At this stage, they more closely resemble their near relatives, the boobies. Over the next five years, they gradually transition into their white adult plumage, with varying degrees of brown or black marking them out as subadults. These birds can often be seen hanging out in gangs near nesting sites in the summer.

Subadult gannets
Subadults often hang out in non-breeding clubs on the edge of colonies

There are two southern species of gannet which look very similar to ours. Cape gannets breed on small islands off South Africa and Namibia. Unlike northern gannets, adults have black tails and black extending over a larger area of the wings. Australasian gannets, meanwhile, breed around Australia (excluding northern coasts) and New Zealand. They are similar to Cape gannets but have a mix of black and white in the tail.

Bird Cities

Anyone who has been lucky enough to visit a gannet colony knows just how incredible they are. Some contain thousands of pairs, all nesting just a beak’s length apart from one another. This is despite the fact that they are to some extent extremely intolerant of each other. If colonies are on flatter island tops rather than sheer cliffs, birds with central nests run the gauntlet of hundreds of pecking beaks to get back to their nests after feeding trips. Juveniles are also rarely left unattended. Neighbouring birds frequently attack and even kill chicks when there is no parent to fight back.

Gannets pair bonding
Pairs frequently reaffirm their bonds by fencing beaks and sky pointing

Colonies are full of the guttural calls of birds grousing with each other or greeting a returning mate. Monogamous birds that mate for life, pairs perform elaborate displays to reaffirm their bonds after each fishing trip. Birds typically fence with their bills, ‘sky-point’, bow and entwine their necks in addition to grooming each other. Pairs lay a single egg each year, with chicks usually hatching in late May or early June.

Gannet colony
Gannets nest a beak’s length away from each other

At present there are 21 colonies in the UK and Ireland. Most are on offshore islands such as Grassholm off South Wales, remote St Kilda and Sula Sgeir west of the Scottish mainland and the Bass Rock off Lothian. Bass Rock is actually the world’s largest northern gannet colony with approximately 75,000 nests recorded in the last census of 2014. Because this colony is the most comprehensively studied, it also gives the bird its species name, bassanus.

Bempton Cliffs
Bempton Cliffs in Yorkshire is the UK’s largest mainland colony

Our largest mainland colony is at Bempton Cliffs in Yorkshire. The last survey in 2017 counted over 13,000 nests there, nearly 10,000 more than in the 2003-2004 census. There are small colonies in Norway, Germany, Iceland, the Faroes, France and the Channel Islands. Across the Atlantic, eastern Canada has six colonies. In late August or early September, European birds disperse from their breeding sites to roam the seas south to the Bay of Biscay and West Africa. Canadian birds may go as far south as the Gulf of Mexico.

The sights and sounds of the Noss gannet colony, Shetland

Feeding Frenzies

One of the gannet’s most characteristic behaviours is its feeding strategy. Birds will first of all look for likely feeding spots using a mix of gliding and powerful wing beats to cover long distances. They often look for other bird aggregations, whale and dolphin activity or fishing boats to find fish shoals. Most birds forage between 100 and 150 kilometres from the colony during the breeding season. A small proportion, though, travel as much as 300 kilometres or more away. Males and females take it in turns to forage away from the nest. Fish species that can be caught reasonably near the surface, such as sardines, herring and anchovies, make up the bulk of their diet. Superb binocular vision helps them locate fish and also judge distances accurately.

Fishing gannets are a spectacular sight

Once they find a shoal of fish, they put their dramatic feeding technique into action. This involves folding their wings tightly back to form an arrow shape as they dive from heights of up to 60 metres into a shoal. Dives can reach speeds of 100 kilometres an hour which helps them reach greater depths than surface-diving birds such as members of the auk family. A series of air sacs under the skin and a reinforced skull cushion the impact. Internal nostrils prevent water entering at high pressure, and a third, or nictitating, eyelid protects their eyes. Under the water, gannets are able to swim powerfully to catch prey. They swallow this to take back to the waiting chick. Whether watched from shore or, even better, a dedicated boat trip, the sight of a host of gannets diving for food is an awe-inspiring experience.

Fishing gannet
Fishing gannets fold back their wings to become extremely streamlined

From Boom to Bust?

The UK is extremely important for gannets and holds nearly two thirds of the world’s population. Prior to last year’s avian influenza outbreak, more of which in a moment, gannets were bucking the trend of most seabirds. A range of seabirds including kittiwake, herring gull, fulmar and puffin have suffered serious declines in recent years as climate change and overfishing affect food supplies. Gannets, however, have proved more resilient and their numbers have been increasing. This means that new colonies have sprung up in the UK and Ireland over the last few decades, including on Ireland’s Eye off Dublin and St Abb’s Head on the east coast of Scotland. The St Abb’s Head colony is an overspill from the growing Bass Rock population. The entire UK population has grown by approximately 34% between 2003-4 and 2013-15 according to the Joint Nature Conservation Committee.

Bass Rock
The Bass Rock in the Firth of Forth is the world’s largest colony. It has overspilled to form a new colony at St Abb’s Head

But despite this, not all is rosy in the gannet garden. A range of threats could halt and then reverse the population increases of the last few decades. Gannets were one of the worse hit species during last year’s avian influenza, or bird flu, outbreak as a result of their tightly packed colonies. Thousands of gannets, along with many other seabirds, died around the North Atlantic in 2022, and the virus has now reached South America and Africa. As gannets only have one chick a year, populations could take a long time to recover. One glimmer of hope is that some birds do seem to survive infection. Recent research shows that gannets displaying unusual black irises instead of pale blue ones have had bird flu but survived. Conservationists are awaiting the 2023 breeding season with trepidation.

Gannet foot
The beautiful foot markings can be seen on this bird flu victim

Bird flu isn’t the only concern, however. Chemical and plastic pollution pose a huge threat to all organisms using the sea and gannets are no exception. Scientists estimate that, globally, 90% of seabirds ingest plastic. Not only can this block digestive tracts and puncture organs, but microplastics are linked to increased vulnerability to disease. Discarded fishing gear is another issue. As well as seaweed, vegetation and mud, gannets often use nylon fishing rope, and both young and adults frequently become entangled, often fatally. The number of birds trapped on Grassholm alone means the RSPB has to visit at the end of the breeding season each year to cut birds free. Gannets are also vulnerable to drowning as bycatch in fishing nets or on longlines. And like many other seabirds, gannets now have to travel further from the nest to forage as climate change moves fish stocks further north.

Gannets in flight
As fish stocks deplete or move with overfishing and climate change, gannets must forage further from their colonies

Glorious Gannets

They may be noisy, smelly and grumpy at their breeding colonies but away from the nest, gannets are majestic seafarers with a hugely impressive hunting technique. Time sat on a clifftop watching them fishing is time well spent. Their recent successes and robust appearance, however, belie an uncertain future. Bird flu, pollution, fishing practices and climate change all threaten this incredible seabird, along with many others. Gannets are a perfect illustration of why we can’t be complacent when it comes to nature. What is abundant now can very quickly become rare or extinct if we aren’t vigilant.

Further Reading

The late Bryan Nelson was an authority on gannets. His book, The Atlantic Gannet, is an extremely readable, yet comprehensive, study on the northern gannet. Although out of print, there are plenty of second-hand copies available online.

Hermaness gannets
Gannets at Hermaness, Shetland

Orcadian musician Erland Cooper’s beautiful 2018 album Solan Goose is named for the gannet and the title track is a wonderful homage to the bird. Oystercatchers (shalders), fulmars (maalies), puffins (tammie nories) and great skuas (bonxies) are just some of the other birds featured.

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