Birds of a feather stuck together

BLUE TITS raised a brood in a nestbox at Wicklow Montessori School this summer.

The pupils of fifth class watched the baby birds preparing for their first flight.

According to 11-year-old Sophie Hopkins, the chicks were poking their heads out of the box when, suddenly, one of them popped out. Although flapping its wings and fluttering like a normal chick, it fell to the ground immediately. When the little bundle of feathers was examined it turned out to be not one, but two, birds. They seemed to be joined at the hip; at any rate the teacher, Hayley Doyle, couldn’t separate them. The chicks were put back in the nest. Twenty-four hours later, the box was empty. All of the little birds, including the joined pair, seemed to have fledged. Photographs of the strange duo were sent to RTÉ’s Mooney Show.

So, were the two little blue tits what are known as ‘Siamese’ twins? Chan and Eng, born in Siam in 1811, gave the condition its name. Joined at the breastbone by a piece of cartilage, their livers were fused but, if the pair were alive today, they could easily be separated. Adopting the surname Bunker, they took part in shows around the world. Settling in the United States, they became well-off and married two sisters, fathering 22 double-first cousins. In January 1874, Chang awoke in the night to find his brother, who was suffering from pneumonia, dead. He died a few hours later.

Immediately after conception, cells begin multiplying. A separation between cells at this early stage can result in the development of two embryos. If the zygotes don’t separate fully at the initial stage, conjoining occurs. Another theory holds that complete separation takes place but stem cells of the two zygotes somehow become intertwined. Conjoining occurs once or twice in every 100,000 human births but only about a quarter of Siamese twins survive.

Polycephaly or ‘many-headedness’ features in mythology. Cerberus was a three-headed dog who guarded the gates of Hades. The Hydra, a water-snake with poisonous breath, had nine heads. If you cut off a head, two more would grow in its place. The Hydra myth is interesting because conjoining is especially common in snakes. It has also been recorded in turtles and crocodiles. Determining the extent of the disorder among wild creatures is difficult; few pairs of conjoined animals survive long enough to come to light. Not surprisingly, most of the recorded cases involve dogs, cats and aquarium fish. Cases of Siamese cows, sheep and pigs are recorded from time to time.

The condition has been found in farmyard chickens and domestic geese but few cases of conjoining have been seen in wild birds. A two-headed partridge was examined scientifically in Boston in 1894. In July 2008, what appeared to be a pair of Siamese swallows fell from a nest in Arkansas. A photograph of them appears on the National Geographic website. Apart from the species difference, the pair seem almost identical to the Wicklow blue tits.

The Arkansas birds were thought to be joined at the hip because they seemed to have only three legs between them. When one of the swallows died, the other was put down. X-rays revealed the presence of a fourth leg and established the pair had shared no skeletal parts or internal organs. It’s been suggested the hidden leg had become embedded in a wound in the body of the other bird and tissue had grown over it.

The Wicklow chicks have disappeared, so we will never know why they were stuck together. There can be up to a dozen baby blue tits scrambling and tumbling over each other in a very confined space just before fledging. Legs and wings can easily become intertwined. Young inexperienced birds might be unable to extricate themselves from a tangle of limbs. If the pair were conjoined, they could not have flown away. Yet the box was empty next day. It’s possible that they managed to leave the nest and that a cat or magpie carried them off. However, it seems more plausible that they had become entangled but managed to free themselves.