British Wildlife of the Week

Barnacle Goose

A barnacle goose
Image Source: Bengt Nyman

Barnacle goose. Goose barnacle. One is a migratory bird; the other a sedentary crustacean. Although differing in almost every single respect, these two animals, if their names are anything to go by, seem to have a hidden connection. And indeed they do – even if it’s only an imaginary one.

Barnacle geese primarily breed in the Arctic Circle – in Greenland, Siberia and Svalbard – and fly south for the winter. Today, a few spend the whole year in the British Isles and even breed here, but several hundred years ago they were exclusively winter visitors. Even now, around 100,000 birds migrate to Britain and Ireland in huge, noisy flocks every year to take advantage of our comparatively mild winters. Because these geese were never around in the summer, and their breeding grounds in the far north were never observed, the people of Britain never saw them mate or lay eggs.

Long before the science of migration was understood, all sorts of strange theories were suggested to explain the annual arrival of barnacle geese – and their unexplained disappearance the following spring. For centuries, it was even believed that these geese bred underwater and hatched from barnacles that washed ashore on driftwood during the autumn. Though this belief seems outlandish now, there are indeed some large black-and-white barnacles that could, with the aid of a vivid imagination, be thought to resemble small geese in shells. The historian and churchman known as Gerald of Wales, writing in the 12th century, even claimed to have personally witnessed the miraculous transformation from barnacle to goose during a tour of Ireland, after which they fell into the water or flew away.

‘I have frequently seen, with my own eyes, more than a thousand of these small birds, hanging down on the sea-shore from a piece of timber, enclosed in their shells and already formed.’

Gerald of Wales
A large number of goose barnacles exposed at low tide
Goose barnacles are so named because their beak-like shell sits atop a long black stalk that is said to resemble the neck of a goose.
Image Source: Tom Page

The Catholic Church forbade the consumption of meat (though not fish) on fast days and Fridays. Because of the barnacle goose’s supposedly shellfish origin, it was considered to be a kind of fish and therefore not ‘born of the flesh.’ Designating this plump, tasty bird as a fish for culinary purposes made it permissible to eat on fast days when other flesh was forbidden, without worrying about committing a sin.

If you think this simply sounds like a convenient way of getting around the dietary rules of Christianity, perhaps you are right. Maybe our ancestors weren’t as foolish as we might initially have thought. Rather than genuinely thinking geese and barnacles were the same species, perhaps a crafty cleric noticed the vague similarity between them and decided he could use this as a loophole to make eating the birds acceptable.

Not everyone was convinced, especially those in high places. Pope Innocent III forbade eating the meat of these geese during Lent because he deemed them to live and feed like ducks and thus could not be regarded as differing in nature from other birds. But it seems that his command did not reach everywhere because in some places the belief that barnacles were essentially geese embryos persisted well into the days of when scientists started classifying animals and giving them official names. Thus, today we have both the barnacle goose and the goose barnacle.

A pair of barnacle geese on a rock
Even well into the 20th century, long after the true nature of both barnacles and geese had been discovered, Catholics in County Kerry in Ireland who abstained from meat during Lent could still eat barnacle geese because it qualified as fish.
Image Source: Needpix

Like many geese, barnacle geese form life-long, monogamous relationships. But before they settle down, youngsters play the field. When they reach one year old, they engage in ‘mate sampling’ – forming short-term liaisons with several members of the opposite sex. They may keep ‘dating’ in this way for a couple of years before finally finding a suitable mate to settle down with and raise offspring. Once they have found this perfect partner, though, they will mate for life and find each other again when every breeding season returns. For monogamous animals, it pays to look around for the best quality mate before making a firm commitment. And this strategy certainly seems to work – the annual ‘divorce rate’ among barnacle geese is a mere 2%.

In the next British Wildlife of the Week, as Christmas gets ever closer, we’ll be looking at a famous festive (and parasitic) plant – mistletoe.


  • Jason Woodcock

    With a background in conservation and animal behaviour studies, Jason's passion lies in the natural world. He adores all things nature and enjoys nothing more than spotting rare and interesting species out in the wild. He has also worked in a zoo and knows plenty about keeping the animals inside our homes healthy and happy, too.

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