Nests and nest building in birds.

Bird nests have long attracted human interest, both as beautiful creations and as important constructions. They are important constructions because avian parents use them to protect their developing eggs and young from the dangers presented by the elements and predators. Despite sharing these protective functions, however, bird nests can be remarkably structurally variable, being built from a wide diversity of materials, and placed in all manner of locations. For example, male Australian brush turkeys scrape material into large nest mounds, woodpeckers excavate holes, storks build stacks, sparrows and swallows build cups (but of different materials), while weavers weave their famous hanging baskets. Nests might be built in bushes or holes in trees, dangle from a branch, or sit on the ground. They might be solitary and hidden, or conspicuous, together housing hundreds of families (Figure 1).