Master builders

With only instinct to guide them and only bills to serve as tools, birds construct nests of amazing complexity. A nest may take weeks to build and involve thousands of flights in search of suitable material. Some birds use whatever comes to hand – even string, nails, plastic bags, or old clothes. Others are much fussier. Hummingbirds build nests from spider’s silk one strand at a time, while swallows collect a certain kind of mud from the edge of puddles.

Cup nest. Most birds use a sequence of movements to create a cup-shaped nest with a snug hollow in the middle. First, they roughly organize the material, with softer items like feathers on the inside. Then they sit in the nest, and turning round and round, push themselves against it to form a perfectly sized cup.

Three houses. Woodpeckers make their homes by drilling holes in trees with their chisel-like bills. Boring through solid wood is hard work, so males and females work together, taking up to a month to complete the task. Instead of lining the nest with soft feathers or leaves, they finely chip the inner wall to make a cushion of sawdust.

Less is more. For many seabirds, a nest is little more than a scrape in the ground or a rocky ledge on a cliff. Gentoo penguins build simple mounds of pebbles, sticks, and grass. To impress their mates, the males collect pebbles of the same size and colour and arrange them in a neat ring around the nest.

Mud hut. Providing it stays dry, mud is an excellent nesting material. Ovenbirds use a mixture of mud, dung, and straw that sets rock hard under the sun, keeping out all but the strongest egg thieves. Their dome-shaped huts always face away from the wind and have an ingenious barrier inside the entrance to block draughts.

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