Common Cranes (Grus grus) weigh 9 to 13 lbs (4-6 kg) as adults. Juveniles can be recognized by their colour. Their feathers are an ochre-yellow colour all over their body and they do not yet have the typical black bun tail. During the first three years, their appearance changes to resemble the adults increasingly to the point where they take on the ashen livery characteristic of their species. The young have brown eyes at first, which become increasingly red as the years go by. Common Cranes are monogamous and couples remain united for life.