All owls lay white eggs. Owls lay their eggs in an existing nest, taking it over from other birds. Owls lay between one and thirteen eggs, but three or four are most common. There are around 250 species of owls, and they are broken down into two families: true owls, called Strigidae, and barn owls, called Tytonidae. Owls mostly eat small mammals, insects, and birds, but some species hunt and eat fish. Owls are solitary and hunt at night, and they are easily recognized by their large, broad heads. A group of owls are called a parliament. The feathers of an owl have adapted to fly silently, making it easier to catching prey.