The common coquí or coquí (Eleutherodactylus coqui) is a species of frog endemic to Puerto Rico belonging to the family Eleutherodactylidae. The species is named for the loud call the males make at night. This sound serves two purposes. "CO" serves to repel other males and establish territory while the "KEE" serves to attract females. Since the auditory systems of males and females respond preferentially to different notes of the male call, this is an example of a sex difference in a sensory system. The common coquí is a very important aspect of Puerto Rican culture, and it has become an unofficial territorial symbol of Puerto Rico. Taxonomy The common coquí was described as a species new to science by Richard Thomas in 1966. It belongs to the genus Eleutherodactylus which in Greek means free toes. This family is also known as the "robber" or "thief" frogs. This genus contains 185 species, which are found in the Southern United States, Central America, South America, and the Caribbean. It is part of the Order Anura, which includes all frogs and toads. The scientific name of the Common coquí, Eleutherodactylus coqui, was first described by Spanish naturalist José Félix de Arroyo de la Cuesta in 1875 (Arroyo de la Cuesta, 1875). The genus Eleutherodactylus, of which the Common coquí is a member, is the largest genus of frogs in the world, with over 700 known species. The Common coquí is closely related to other members of the Eleutherodactylidae family, including the Eleutherodactylus jasperi and the Eleutherodactylus portoricensis. These species are all native to Puerto Rico and are distinguished from each other by their physical characteristics and vocalizations (Joglar and López, 1997). This taxonomic classification reflects the evolutionary relationships between the Common coquí and other species within the animal kingdom. Description Appearance and Lifespan Full-grown male coquís measure, from snout to vent, from 30 to 37 mm, with an average of 34 mm, while full-grown females measure from 36 to 52 mm, with an average of 41 mm. The location of the frog also effects the size, for example the higher the elevation, the larger the coquis become. The size differences between sexes are a result of additional energy consumption related to breeding behavior by males. Coquís are muddy-brown in mottled coloration on the top with rust-tan flanks and a light-gray belly. As tree frogs, Coquís possess sticky pads on the tips of