Gulls and hummingbirds are oviparous, which means they reproduce through eggs. Males do not have external reproductive organs, but two internal testes to produce sperm. Females have two ovaries, but only one is functional, producing ovules. Embryos of both birds take nourishment from the egg yolk, to complete their development. Oxygen passes through the porous egg shell.
Many bones of gulls and hummingbirds are light, hollow and adapted for flight. Both birds have a pygostyle, which is a set of fused vertebrae in the posterior region that support the tail musculature and feathers. The respiratory system contains lungs and air sacs, which are used as an extension of the lungs, storing air. Like most birds, gulls and hummingbirds have a high oxygen demand, because of the amount of energy they spend flying.
Although gulls and hummingbirds have distinct diets, based on fish and nectar respectively, both birds show similar digestive systems, with an alimentary canal (esophagus, stomach, intestines) and accessory glands, such as the liver and pancreas. Like most vertebrates, gulls and hummingbirds have a four-chambered heart, an adaptation that maximizes oxygen transport throughout the body. Their average body temperature is 105 degrees Fahrenheit.
The most important sense for gulls and hummingbirds is vision. Like most birds, they have acute and wide-field eyesight, as well as larger eyes in relation to their head size. Gulls and hummingbirds have a third transparent eyelid, called nictitating membrane, which they use to keep their eyes lubricated. The numerous nerve connections these birds have between their eyes and brains is the main reason for a superior eyesight.