A tawny owl’s eyeballs are almost as large as a human’s, even though its skull (without feathers) is barely the size of a golf ball. The eyeball is shaped like a saltshaker rather than a sphere, to allow space for the largest possible retina. The retina has many more light-sensitive rods than detail-focusing cones, enabling them to see when the light level falls to almost nothing. A long-eared owl’s eyes are so sensitive it can locate a stationary mouse in light levels equivalent to a football stadium illuminated by a single candle. The downside is that they can’t move their eyes. If they want to change their range of view, owls have to swivel their head. If they want to judge an object’s position accurately, they bob their head around, reading it from slightly different angles.