Some birds line their nests with soft materials to keep the eggs warm.

The longer version

Eggs lose heat to whatever they touch, so a lining of down, hair or fine plant fibre cuts conduction and holds a layer of still air around the clutch. Still air is a poor conductor, which is exactly what insulation needs. The parent adds the lining gradually and often keeps adding it through incubation.

Lining also cushions eggs so they do not crack against twigs and stops them rolling out of a deep cup. Birds nesting in cold regions build thicker, better insulated structures than their relatives in warm ones. Feather linings are gathered during moult, when loose feathers come away most easily.

Where this entry sits

Here you will find feathered trivia about flight, migration, nests, eggs, and the songs birds sing. Expect short surprising facts on penguins, owls, hummingbirds, and other familiar birds from gardens, forests, wetlands, and distant coastlines. The full list sits on the Birds page, where every entry is listed in order.