The male and the female birds, the cob and pen, usually attempt to mate for life, although it is not true to say that if one of the birds were to die the other would necessarily pine away. It is possible for an adult bird to find an alternative mate. Mute swans can be very aggressive in defence of their nests and are highly protective of their mate and offspring. Most defensive attacks from a mute swan begin with a loud hiss and, if this is not sufficient to drive off the predator, are followed by a physical attack. Swans attack by smashing at their enemy with bony spurs in the wings, accompanied by biting with their large bill, while smaller waterbirds such as ducks are normally grabbed with the swan's bill and dragged or thrown clear of the swan and its offspring.