Life on the tundra has forced birds to adapt and find alternatives to nesting in trees. While many of their southern relatives nest in tall trees, arctic hawks, eagles, and falcons nest on cliff faces, which give them a good view of the surrounding countryside, enabling them to search for prey. These areas are often the first to be free from snow in the spring, allowing the birds to nest as early as possible. They are also inaccessible to most mammalian predators, although they must be defended against other birds. Some other birds also nest on cliffs, or in crevices in smaller rocks or boulder piles where they can build a secure nest, protected from the weather as well as from predators.