Swans are often seen gliding gracefully across water, but what is less well known is that they may have a trick for getting an extra boost of speed — windsurfing.
Olle Terenius, a Swedish biologist, first noticed something strange when he saw what looked like a white plastic bag scudding across a lake. It was actually a species of swan called a mute swan that was travelling remarkably fast. The bird had arched its wings over its back like a sail and caught the wind, enabling it to skim across the water. Later, Terenius recorded another mute swan skimming across the water for a quarter of a mile.
Mute swans are heavy birds, with some weighing about 10 to 12kg. They usually paddle leisurely with their big webbed feet at a typical speed of 1.6mph. They can paddle faster but not for any great distance because it takes too much energy.
Windsurfing enables these swans to almost double their speed at little extra cost in energy. Terenius calculated that if the swans tried to achieve that speed by paddling they would use up vast amounts of energy — 12 times more than they use at rest. That is the equivalent of a human playing a game of squash. The study of the swans was published in The Wilson Journal of Ornithology.
Mute swans are not the only creatures that get a burst of speed by windsurfing. The common spider, and many other small spiders, are also skilful windsurfers. Most can stand on water using their water-repelling feet and can then sail by thrusting their abdomen upwards to catch the wind, or point a pair of forelegs into a V-shape. They can even manoeuvre in turbulent water. On land they show none of these skills, suggesting that they are used solely for sailing across water.
In addition, some small spiders are able to throw out a strand of silk to act as an anchor on nearby objects. This study was undertaken by the Natural History Museum, London, and published last year in BMC Evolutionary Biology.