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Why do some swans only paddle with one leg, with the other leg tucked up under the wing?

Sent in by Shelah Walster, Swadlincote, Derbyshire

It is normal for swans to swim with one leg tucked onto their back. People are often concerned that the leg is broken or deformed but the swan is perfectly fine. 

Swans will often stretch one of their legs whilst swimming and instead of putting it in the water, they will tuck it up onto their back. 

It has been suggested that this behaviour may play a role in helping to regulate the body temperature of the bird. The legs and feet are the only part of the swan not covered in feathers so the blood vessels are in closer contact with the air. The large surface area of the webbed foot makes it easier for heat to be transferred from the body to the air, cooling the swan. This heat exchange could also work the other way, with the feet absorbing heat from the air to warm the bird.     

From February onwards swans will start preparing to breed although the eggs are usually laid in late April/early May. Breeding pairs will start re-establishing their territories and any remaining youngsters from the previous year will be chased away. These young birds will join up in flocks with other non-breeding swans, in whose company they will remain for two years or longer until they are ready to breed themselves.

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