Honey bees rely on their sense of vision to locate flowers. Bees see colors in the spectrum ranging from ultraviolet to orange, but do not see red (red flowers are visited by birds such as hummingbirds). The flower advertises itself to the bees with colorful petals, many of which have shiny patches of ultraviolet that humans can't see without using special equipment. These ultraviolet patches are called "bee guides" or "nectar guides." Like airport runway lights, these ultraviolet regions guide the bees to the nectar. The shape of the flower is also important. Some flowers have flat areas for ease of landing by bees, and others have elaborate modifications to ensure that pollen sticks to any bee that visits.