Birds have different features that help them survive. Their feathers come in different shapes, colors and sizes. Flight feathers help birds fly while down feathers keep them warm. Birds also have different beaks, feet and claws suited to their diets and habitats. They build various types of nests using materials like twigs, grass or mud depending on the species. Penguins build nests from stones and sometimes dig burrows to protect their eggs in icy climates lacking plants.