Why do some birds build nests in unusual places?

Bird nest sites vary widely because each species faces different survival challenges. A bird may choose a cliff ledge to keep predators away, a tree cavity for shelter, or a burrow to avoid heat and hunting risk. Some urban birds nest on buildings because these structures mimic cliffs or ledges. The best site balances safety, access to food, and the needs of eggs or chicks. Nesting behavior is one of the most flexible parts of bird life.