The Golden Eagle is probably the best known of all the birds of prey. It is a magnificent bird, up to 3 feet in length and with a wingspan of up to 8 feet. Golden Eagles patrol enormous areas of remote mountainous country throughout the northern hemisphere. They are long-lived birds which pair up for life, usually returning to the same nesting site each year. A predatory bird as large as this obviously cannot nest anywhere. The most favoured place for an eagle to build its eyrie is on an inaccessible ledge of a sleep cliff, commanding a good view of the surrounding countryside. Here the eagle cannot be approached unawares. In North America eagles seem to prefer to nest in trees. As the eyrie is added to year after year, the weight of sticks sometimes becomes too great, and the nest may overbalance the tree.