Geckos occur in various patterns and colors, and are among the most colorful lizards in the world. Some species can change colour and may be lighter in colour at night.[citation needed] Some species are parthenogenic, which means the female is capable of reproducing without copulating with a male.[citation needed] This improves the gecko's ability to spread to new islands. However, in a situation where a single female gecko populates an entire island, the island will suffer from a lack of genetic variation within the geckos that inhabit it.[citation needed] The gecko's mating call sounds like a shortened bird chirping which attracts males, when they are nearby.[citation needed] Like other reptiles, geckos are ectothermic,[10] producing very little metabolic heat. Essentially a gecko′s body temperature is dependent on its environment. Also, in order to accomplish their main functions—such as locomotion, feeding, reproduction, etc.—geckos must have a relatively elevated temperature.