If only this mongrel swan could talk

I RECEIVED an email this week about a mongrel swan in Cork. It came from an unlikely source, Maria Weiloch, a swan expert at the Gdansk Ornithological Station.

Piotr Tadeusz, a Polish birdwatcher living in Ireland, had sent her photographs of a strange-looking swan “on a small lake between Waterford and Middleton”. Piotr couldn’t name the location, so I rang Cork ornithologist Pat Smiddy. It turns out that the bird has been around for some time; Pat had recorded two strange young swans at Loughaderra, near Castlemartyr, in May 2006. One of them disappeared the following July. The other, Piotr’s bird, stayed on.

The familiar resident of Irish rivers and ponds is known as the “mute” swan. Adults have an orange-red bill and a black knob, known as a “berry”, on the forehead. When the bird is swimming, its tail points upwards. Another swan, the whooper, visits Ireland in winter. It keeps a low profile and is not well known to the public. The bill is black and yellow. There is no berry and when the bird is swimming, the tail curves downwards. Whoopers “honk” loudly.

When the strange swans first arrived, Pat heard them honking. Piotr’s photographs show a bird with the bill of a whooper and no berry. However, closer inspection reveals a pink patch towards the base of the bill and the bird’s tail points upwards like that of a mute. It’s clearly a cross between species.

Hybrid swans, though rare, have been recorded in Sweden and in Britain. Maria, who has been studying swans in Poland for decades, has come across several cases there. She even managed to fit neck-collars on hybrids; one of the birds travelled to Germany where it joined a flock of mutes.

The Cork birds were not the first ones to turn up in Ireland. Two visited Dundalk a few years ago, raising some intriguing possibilities. During the winter of 2003/2004, there were two hybrids among a flock of mutes at the docks there. Research in Sweden has shown that mute-whooper hybrids can be fertile. Did one of the Dundalk birds manage to find a partner, whether mute or whooper, and breed? If so, are the Cork birds related to the Louth ones? Are they the offspring of one of them? Swans are notoriously conservative when it comes to sex; if you want monogamy, it’s said, you should marry a swan. Why then do some individuals develop liaisons with partners which are not even members of their own species? Mutes and whoopers don’t look alike and their lifestyles are quite different. In winter, mute and whooper flocks have separate haunts, although there is some mixing between them. Irish mutes remain here throughout the year, whereas all of our whoopers, apart from a few stragglers, go to Iceland to breed. There are no mutes there. These differences should ensure that mixed marriages don’t occur. On the other hand, the world’s seven swan species are so closely related that they belong to the same genus.

Are hybrids the result of human meddling? Captive birds behave differently from wild ones. A well-known whooper and mute pair in Copenhagen Zoo during the 1940s were inseparable. Potential mates of their own species, placed in adjoining pens, were no threat to their marriage. In the 1970s, swans of every species, except one, had interbred in the collections of Britain’s Wildfowl Trust. Only the black-necked swan, a native of South America, seemed impervious to such liaisons. Then a black-necked and a mute began an affair at Turin Zoo.

When chicks are raised by foster-mothers in zoos, they may become imprinted on the adoptive parent. When they become adults, these youngsters seek a partner of the foster parent’s species rather than their own, giving rise to hybrids. So are the parents, or grandparents, of Piotr’s bird escapees? There is no wildfowl collection in Ireland from which they might have come. However, whoopers fly long distances and a tendency to travel could be inherited from the whooper side of a hybrid’s family. Piotr’s bird, therefore, is probably foreign. If the swan could talk, it would have an interesting tale to tell.

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