The adventures of our swans

According to tradition Richard Lionheart, returning from a crusade, brought the first mute swans to England. Later, the Normans took them to Ireland.

Swans were sedentary and wouldn’t cross the Irish Sea, or so it was thought. Isolated for centuries on this wet, windy island at the western edge of the species natural range in the mildest climate their species encounters, our swans must have developed ‘Irish solutions to Irish problems.’ What these local peculiarities were wasn’t known and this prompted me to embark on a study of their lifestyles.

British swans are ‘stay-at-home’ birds; few of them travel much but there were a few notable exceptions. One was a bird ringed in Coventry, which turned up in Rosscarbery, Co Cork, in 1976. That raised an intriguing possibility. Mute swans, clearly, were quite capable of crossing the sea. So, did they colonise these islands on their own, without help from the Lionheart and the Normans?

Finding answers to this, and many other, questions took years of research. It involved catching over 1,500 swans around Dublin and Wicklow, fitting rings to their legs and tracking them to record the details of their lives. Nests were located, mating behaviour examined, clutch and brood sizes logged, survival rates calculated, carcasses dissected etc.

It soon emerged that Irish swans were more adventurous than their cousins across the water; they travelled further and moved more often. Dublin-ringed ones followed the coast as far north as Donegal and south to Cork. This raised an obvious question; did they cross the Irish Sea? In May 1984, less than a year into the study, a swan ringed at Swords, County Dublin, was found dead at the Menai Straits in Wales. It was the first known instance of a swan crossing from Ireland to Britain. Over the next decade, five more sea crossings were logged. Only a minority of ringed bird sightings are reported, so many birds moving to Britain must have gone unrecorded. Swans traverse the Irish Sea but how many do so?

A paper in the current edition of Ringing & Migration helps answer this question. The authors examined the movements of swans ringed on the Isle of Man. That island in the midst of the Irish Sea, serves as an aircraft carrier for travelling birds. The swans ringed around Dublin were a bit too far south to avail of it, but those living further north, on both sides of the Irish Sea, could do so.

Stephen Christmas and colleagues began ringing swans on the Isle of Man in 1988. They had ringed 119 by the time they wrote their paper. Of these, 23 (19%) were recorded subsequently away from the island. Eight came to Ireland, a 45km crossing at the nearest point. Eight turned up in Lancashire or Merseyside, having flown at least 50km over the sea. The Scottish coast is only 20km from Man. Four Manx ringed swans were found in Scotland, up to 190km from home. Three swans visited Wales, 70km to the south. Growing up on a relatively small island with few breeding territories available, young Manx swans have little option but to emigrate.

Some movements resembled the shopping trips to London or New York made by nouveau-riche Irish people during the heyday of the Celtic Tiger; 10 of the 23 travellers returned to Man. One swan crossed the Irish Sea four times. Birds tended to travel when they were young and did so without their parents; 48% of the voyagers were less than a year old when ringed. Some spent a year or two away before returning home. A bird which visited Dundalk was found back on Man seven years later.

The wanderlust, however, seems peculiar to Isle of Man swans. Of 6,921 swans ringed in the northwest of England, only eight (0.1%) were recorded crossing the sea. It’s clear, however, that the ancestors of our swans needed neither the Lionheart nor the Normans to get here.

Movements of Ringed Mute Swans across the Irish Sea. Stephen Christmas et al. Ringing & Migration. 2014.

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