As skies are filled with millions of migrating(迁徙) birds, European scientists say the seasonal wonder appears to be strange: The fatter the bird, tile better it flies.
    The results of their study led to a theory opposite to a central one of aerodynamics (空气动力学), which says that the power needed to fly increases with weight.
    For birds, obviously, the cost of flying with heavy fat is much smaller than we used to think. Researchers found that red knot wading birds double their normal body weight of 100 grams before making their twice-a-year nonstop flight between the British Isles and the Russian Arctic. Distance: 5,000 kilometers.
    Another study in the magazine Nature measured the advantage of flying in an aerodynamic group which allows birds to save energy by flying smoothly and quietly in the lead bird' s air stream.
    Flying in groups, their heart rates were 14.5 percent lower than flying alone, according to Henri, a French scientist. The findings help explain how birds complete difficult migrations. Researchers had thought that thinner, stronger birds would have the best chance to survive.
    The first study suggests that building up fat to be burnt as fuel during the migration is worth more than the energy it takes to carry the additional weight.