'Brexits' occur in animal kingdom too through migration

Brexits aren’t confined to EU politics, they occur in the animal kingdom also. 

Bears, for example, are a tightly-knit group, with only eight species worldwide. Around 150,000 years ago, brown bears living in the far north severed their ties with the rest of their tribe. Hunting seals on the polar icecap, they evolved into marine predators. The pads on their feet grew little bumps, giving traction on ice and they stopped adding brown pigment to their coats; white hair provides camouflage in snowy environments. Their brexit seemed a wise move back then. Now, however, the ice-cap is melting and polar bears may have to return to their brown bear roots. ‘Grizzlars’, youngsters of mixed brown and polar bear parentage, are turning up.

Birds too have their brexits. The ‘thick-billed guillemot’, of the far north, was re-named ‘Brünnich’s guillemot’ in honour of Morten Thrane Brünnich, a Danish naturalist born in 1737. One visiting Ballyteigue Bay, County Wexford, in December 1986 was very far south of its normal range. Hornøya is a small uninhabited island in the Barents Sea off the north-eastern tip of Norway, 400km beyond the Arctic Circle. Brünnich’s guillemots were among the 100,000 seabirds nesting on the cliffs there last month.

You can easily tell a Brünnich’s from the common species; there’s a white line along the upper edge of its bill. On Hornøya, the Brünnich’s seemed better ‘turned out’ than their cousins; the demarcation between the black upper parts and the white breast was cleaner and sharper. Nor were there dark streaks on the flanks. Guillemots belong to the auk family, the northern hemisphere’s equivalent of penguins. Superb divers and swimmers, they use their wings as fins underwater. However, a good fin makes a bad wing, so auks incur the highest flight costs of any bird. One species, the great auk, abandoned flying altogether. It paid the price; sailors hunted it to extinction. Guillemots, being such poor flyers, are also helpless on land. They can only nest safely on cliff ledges in remote places.

The auk family, like that of the bears, has relatively few species; there are only 23 worldwide. Their distant relatives the gulls, by comparison, have 51. That the common guillemot and the Brünnich’s decided to brexit from each other is odd. Like those of the polar bear, the Brünnich’s ancestors took to fishing close to the polar ice cap, where sea temperatures are below 8C. Such waters are rich in oxygen, supporting abundant plankton and the fish which guillemots eat. There was a price to be paid for such specialisation, however; heat loss. Large creatures cope better in cold environments, which is why polar bears are so big. Brunnich’s guillemot, although larger than its common cousin, can’t afford to become any bigger lest it lose the ability to fly.

The common guillemot’s breeding territory is the smallest of any bird, with up to ten pairs nesting per square metre of cliff ledge. Brunnich’s demand more space; their ledges are less crowded. The habits of the two species, however, are much the same. Both parents feed the single chick. When it’s two to three weeks old, the baby waddles to the cliff edge and peers down at the fearsome waves far below. The father, uttering a special ‘leap’ call, encourages it to jump. When the chick finally takes the plunge, tumbling wingless through the air, he flies down with it. Reaching the water, the two swim out to sea. The youngster won’t return to land for four years. Chicks in our part of the world jump at dusk when it’s harder for predatory gulls to spot them. In Hornøya, with its 24 hours of daylight, there is no protective darkness but most chicks, I was told, wait until the sun reaches its lowest point before jumping. Old habits die hard!

  • I visited Hornøya on behalf of RTÉ’s Mooney Goes Wild radio programme.


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